Meal Replacement Programs

Diet Reference Archive: commercial program category

Meal Replacement Programs

Plans that swap one or more ordinary meals a day, most often 1 or 2, for a shake, a bar or a packaged meal with a known number of calories, while keeping some ordinary food. They are sold mainly for weight loss and for keeping lost weight off.

Family: Commercial programs and products Promoted by: the makers of shakes, bars and packaged meals, and the weight-loss programs built around them First appeared: in published randomized trials by the late 1990s GRADE: Very low for body weight at 1 year, as measured, in adults with overweight or obesity, partial meal replacement plans with support compared with the same support and a food-only diet; this page's judgment. Very low for the same plans without added support, compared with a food-only diet; this page's judgment

ON THIS PAGE

1. In brief
2. Overview
3. In practice
4. For the coach
5. The evidence (opens on request)
6. Mechanisms (opens on request)
7. Risks, contraindications and myths (opens on request)
8. Key terms
9. Review questions
10. References
11. Evidence rating and review record

The summary and sections 1 to 3 are the short version and are open when the page loads. Sections 4 to 6 hold the research detail, the biology, and the cautions. Each of those opens when you select its heading, and you can read the page without opening them. Back to the Diet Reference Archive index.

In brief

What is it? A meal replacement program swaps one or more meals a day, most often 1 or 2, for a shake, a bar or a packaged meal with a set number of calories, and keeps some ordinary food. This page covers that everyday, partial use and names the brands a client is likely to mention, without reviewing each company. Replacing all food with formula products is total diet replacement, a supervised medical treatment described on the Very Low Calorie Diets page, which covers formula programs both under 800 calories a day and at about 800 to 1,200. How many meals a plan replaces and how many calories it supplies are separate questions: a partial plan can still be a low-energy diet.

Does it work? In year-long trials, adults who used meal replacements as part of a reduced-calorie plan lost on average about 1.4 to 2.2 kilograms more than people on the same kind of plan with ordinary food only (Astbury et al., 2019). This page rates the certainty of both results as very low, mainly because the trials varied and the difference could be under 1 kilogram. The difference was less certain at about 2 years, and in a 3-year trial people regained much of what they had lost whether or not they used the products (Lowe et al., 2018). Over a median of 12 weeks in adults with prediabetes or features of metabolic syndrome, a 2024 review rated small reductions in blood pressure and LDL cholesterol moderate in certainty (Noronha et al., 2024). The logged searches found no trial showing that the products prevent heart disease or lengthen life.

Is it safe? That is uncertain, because harms were rarely reported: only 2 of the 23 trials in the main review reported adverse events at all (Astbury et al., 2019). Two cautions matter most. A person taking insulin or a sulfonylurea for diabetes can have low blood sugar when eating changes this much, so the prescriber is involved before the plan starts. If symptoms of low blood sugar come on, the person follows their own treatment plan first, gets emergency help if symptoms are severe or they cannot manage the episode, and then tells the prescriber (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). And a product label is not a care plan for someone who is pregnant or under 18, or for someone with kidney disease, whose needs depend on the stage of the disease, lab results and whether they are on dialysis.

Who should not do it without talking to a doctor or dietitian first? Anyone who is pregnant or breastfeeding, and anyone under 18. Anyone taking insulin, a sulfonylurea, blood pressure medication or warfarin. Anyone with kidney disease. Anyone with a current or past eating disorder. SlimFast's own plan page asks several of these groups to check with their doctor (SlimFast, 2024).

Related pages: Very Low Calorie Diets, Detoxes and Cleanses, Diabetes Plate Method, Mindful Eating. Also related, by name: Optavia, Jenny Craig, Nutrisystem, Multi-Level Marketing Nutrition Programs and WeightWatchers. Full list on the archive index.

1. Overview

What you eat

On a typical plan, 1 or 2 meals a day are a shake, a bar or a packaged entrée with a fixed number of calories, usually made with added vitamins and minerals. The rest of the day is ordinary food: at least 1 meal the person chooses or cooks, and often 1 to 3 planned snacks. Many plans start with 2 replacements a day and drop to 1 for maintenance. The products come as ready-to-drink bottles, powders mixed with water or milk, bars, and frozen or shelf-stable meals. A plan can be a brand's own system, a structure set by a clinic or a trial, or something a person puts together from products bought at a grocery store.

What you avoid or limit

No food is forbidden. What is limited is choice at the replaced meals, which are fixed in portion and calories, and the total for the day, which the plan sets. Plans differ in how much they say about the ordinary meal: some give a calorie range, some give menus, and some leave it to the person. Partial plans are different from total replacement, in which formula products are the only food for a set number of weeks. Total replacement is defined by replacing the whole diet, not by a calorie number; it is a supervised medical treatment, described on the Very Low Calorie Diets page.

Where it came from

Formula products that replace all food were first developed as medical diets, a history told on the Very Low Calorie Diets page. Partial plans, which keep some ordinary meals, were being tested in randomized trials by the late 1990s. A German trial published in 1999 compared a reduced-calorie diet of ordinary food with the same calorie target met by replacing 2 meals and 2 snacks a day with prepared products (Ditschuneit et al., 1999). By 2003, a pooled analysis of 6 trials described the approach as used by millions of consumers (Heymsfield et al., 2003). Large programs then built the products in: the Look AHEAD trial of an intensive lifestyle program for adults with type 2 diabetes included meal replacements in its diet (Astbury et al., 2019).

Industry has been part of this research from the start. A 2019 review of 23 trials lists companies that funded or supported trials it included, among them SlimFast, Medifast, Herbalife, Jenny Craig, Almased and Abbott, and its authors note that many of the trials were funded or supported by industry (Astbury et al., 2019). That is not a reason to dismiss the trials. It is a reason to read them with the funder in mind, and it is part of why this page reports company statements as the companies' claims.

What it claims to do

SlimFast describes its plan as a scientifically formulated plan that "supports sustainable weight loss," and states that average weight loss is "1-2 lbs per week" (SlimFast, 2024). Abbott describes its Glucerna shakes as "meal or snack replacements" that help "manage blood sugar response," a claim it defines as minimizing the blood sugar spike compared with high-glycemic carbohydrates (Abbott, n.d.-c). Huel sells its Black Edition powder as a complete high-protein meal with "all 27 essential vitamins and minerals" (Huel, n.d.). Whether the evidence supports these claims is answered in section 4, not here.

What it gets right

A meal replacement takes the guesswork out of one or two meals. The portion and the calories are printed on the package, so a person who wants to eat less does not have to estimate, weigh or decide at those meals, and the rest of the day stays flexible. Nothing is forbidden, which separates these plans from diets built on banned foods. In 2 trials that measured it, women using fortified products had better intakes of several vitamins and minerals than the comparison groups (Ashley et al., 2007; Phelan, Abrams, & Wing, 2019). And when trials gave both groups the same calorie target, the meal replacement groups usually lost somewhat more weight at 1 year (Astbury et al., 2019). For a client who values structure, these are real reasons a coach can honor without endorsing a product.

How clients describe it, and what it gets confused with

Clients say "I'm doing shakes," "I have a shake for breakfast and lunch," "I'm on SlimFast," "I drink Glucerna for my sugar" or "I have a Huel at my desk." Each of those usually means partial replacement. Some phrases point elsewhere. "I'm only drinking shakes for a few weeks" may mean total replacement, which belongs on the Very Low Calorie Diets page and needs medical supervision. A juice fast or a cleanse is a different thing, covered on the Detoxes and Cleanses page. A protein shake after a workout is a supplement to meals, not a replacement for one. Shakes sold by an acquaintance may come from a direct-selling company, and a client using Optavia "Fuelings" is in a coach-led commercial program; this page describes the general category, not each company or way of selling. Low-carbohydrate shakes may be part of a Ketogenic Diet.

2. In practice

A typical day of eating

SlimFast's plan is a common pattern. It replaces 2 meals with shakes, keeps 1 meal of 500 to 600 calories of the person's choosing, and adds 3 snacks of about 100 calories each; the company puts women at about 1,200 to 1,300 calories a day and men at about 1,500 (SlimFast, 2024). A day on that pattern might be a ready-to-drink shake at breakfast, a cup of yogurt mid-morning, a shake or meal bar at lunch, an apple in the afternoon, and a dinner of baked salmon, brown rice and green beans, with a small handful of nuts in the evening. Trial plans looked similar: in one, participants replaced 2 meals a day for 6 months, then 1 meal and 1 snack (Lowe et al., 2018).

Cost, products, and who profits

Prices were checked on the companies' own pages on October 11, 2026, and are a snapshot from that date. Huel listed its Black Edition powder at $45 a bag, from $2.65 per 400-calorie meal, and its ready-to-drink version from $4.83 a bottle (Huel, n.d.). Abbott's online store listed a case of 24 Glucerna Shakes at $52.89, about $2.20 a bottle, and a case of 16 of its 1-gram-sugar version at $43.96, about $2.75 a bottle (Abbott, n.d.-a). SlimFast's plan page lists no prices, and its shop address returned a password page when checked. Prices for prepackaged meal programs such as Jenny Craig, Nutrisystem and Optavia were not checked for this page. Prices change often, so a client's own receipt is the better guide.

Whether a $2 to $5 replacement costs more or less than the meal it replaces depends on what the person usually eats. The 2019 review of 23 trials found no information on costs to individuals (Astbury et al., 2019). In the trials described on this page that reported it, the products were provided free, so those trials did not test whether people keep buying them (Lowe et al., 2018; Phelan et al., 2018). The companies that make and sell the products profit, along with retailers and the programs built around them. Several have also funded the trials (Astbury et al., 2019). For someone with limited money, ordinary portion-controlled meals can do the same structural job; a registered dietitian can help plan them.

Environmental footprint

The logged searches for this page found no study measuring the greenhouse gas, land or water footprint of meal replacement products or plans. A 2023 modeling study estimated farm-stage greenhouse gas and water footprints for 7 commercial weight-loss diets from their published guidelines and sample meal plans; none of the 7 was a meal replacement plan, so it gives no estimate for the products or for this kind of plan (Neff et al., 2023). The footprint of a partial plan depends mostly on what the products are made from and on the ordinary meals eaten alongside them.

Cultural fit

The ordinary meal can come from any food tradition, which is a strength of partial plans. The replaced meals are the hard part: a shake at the family table, at a shared lunch or during a holiday meal can feel out of place. Trials have been run in North America, Europe, Asia and Australia (Astbury et al., 2019), and one pregnancy trial was delivered in Spanish and English to a group that was 41.6 percent Hispanic (Phelan et al., 2018). Whether a product fits a person's religious or ethical food rules, such as halal, kosher or vegan eating, depends on the specific product and its labeling, which the person checks.

What makes people stop

In a trial in adults with type 2 diabetes, read here in abstract only, the abstract reports that more people stayed in the meal replacement group than in the ordinary-food group and that they rated the plan easier to follow (Cheskin et al., 2008). Use falls when the structure ends: in a pregnancy trial, meal replacement use and dieting behaviors declined significantly after delivery, when the program stopped (Phelan, Wing, et al., 2019). In a survey of 197 Australian health professionals working in weight management, the barriers they named included patients not keeping to the plan and doubts about how long the weight loss lasts (Maston et al., 2020). The reasons clients give in practice, such as tiring of the same flavors, cost, and wanting to eat what the family eats, are observations here, not measured findings.

What happens when you stop

The longer trials show regain. In a 3-year trial in Philadelphia, 262 adults were randomized to behavioral treatment alone, behavioral treatment with meal replacements, or a program that changed the home food environment; all 3 groups lost weight in the first year and regained much of it by 36 months, when average losses were 4.21, 3.06 and 4.49 percent of starting weight (Lowe et al., 2018). In adolescents, the advantage of meal replacements at 4 months was gone by 12 months (Berkowitz et al., 2011). After a pregnancy trial in which meal replacements reduced weight gain, weight retained 12 months after delivery did not differ clearly between groups (Phelan, Wing, et al., 2019). Section 4 gives the 2-year and 4-year results from the 2019 review.

Common variations

Shake-and-meal plans replace 1 or 2 meals with shakes or bars, the SlimFast pattern (SlimFast, 2024). Prepackaged meal programs such as Jenny Craig and Nutrisystem supply portion-controlled entrées instead of shakes; the 2019 review counted Jenny Craig's prepackaged meals as meal replacements (Astbury et al., 2019). Coach-sold programs such as Optavia, and products sold through direct-selling networks such as Herbalife, add a sales and coaching layer; this page does not review them company by company. Diabetes-specific formulas such as Glucerna are designed around blood sugar and carry the company's instruction to use them under medical supervision (Abbott, n.d.-c). Nutritionally complete powders such as Huel are marketed on convenience and complete nutrition, with weight loss as one of several uses the company lists (Huel, n.d.). Total diet replacement is covered on the Very Low Calorie Diets page.

3. For the coach

SCOPE OF PRACTICE

A health and wellness coach does not prescribe, adjust, endorse, or discourage a diet, and does not diagnose or treat. With meal replacements, that includes recommending a brand, a number of shakes a day or a calorie target. The coach helps the client understand what they have chosen, notice how it is going, and decide what to do next. This plan needs the prescriber involved before it starts for anyone taking insulin, a sulfonylurea, blood pressure medication or warfarin. It needs a registered dietitian, working with the care team, for anyone who is pregnant or breastfeeding, under 18, or living with kidney disease, whose needs depend on its stage, lab results and dialysis. A current or past eating disorder means the client's clinician is involved first. A plan that replaces all food is medical treatment, not partial replacement.

Who does what

The physician

Decides whether a meal replacement plan is safe for this person, especially when it lowers calories or carbohydrates enough to change blood sugar or blood pressure. Reviews the medicines that matter most: insulin and sulfonylureas, which can cause low blood sugar when eating changes (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.); blood pressure medicines, because blood pressure fell in meal replacement trials (Noronha et al., 2019); and warfarin, whose effect depends on steady vitamin K intake (MedlinePlus, 2026). Orders and reads the labs that apply, such as HbA1c and kidney function, and decides whether the person needs a supervised program rather than a store-bought plan.

The registered dietitian

Designs a plan that fits the person, including which products, how many a day, and what the ordinary meal and snacks should supply. Checks the protein, sugar, fiber and added vitamins in the products against the person's needs, which matters for diabetes, kidney disease, pregnancy and older age. Plans the move back to ordinary meals, and can build a portion-controlled plan from ordinary food for someone who cannot afford or does not want the products.

The health and wellness coach

Helps the client see why they chose this plan and what they hope it will do, test it against their budget, schedule, family meals and values, and build the routines that make it workable, such as planning the ordinary meal or deciding what happens at a work lunch. Helps the client notice how it is going, including hunger, energy and how they feel about food, and think ahead to what comes after the products. Holds the referral line when medication, pregnancy, age, kidney disease or eating concerns come into the picture.

What a client bringing this diet needs

A client who brings up shakes usually wants something that feels simple and controlled, often after other attempts have felt like too many decisions. Some have seen a friend lose weight on a plan; some were told by a clinician to "try meal replacements." What the coaching conversation can offer is a clear look at the client's own reasons, an honest picture of what the research shows at 1 year and beyond, and a plan they own for the parts the products do not cover: the ordinary meal, the social meals, and the move back to everyday food.

What to ask

• What drew you to meal replacements, and what do you hope they will make easier?
• Which meals feel hardest to manage now, and which would you want to keep as ordinary food?
• How do the products fit your budget, your work day and the meals you share with others?
• Have you talked with your doctor or pharmacist about this, given the medicines you take?
• When you picture 6 months from now, how do you see yourself eating?

Referral red flags

Refer before going further when the client takes insulin, a sulfonylurea, blood pressure medication or warfarin and has not told the prescriber about the plan; is pregnant, breastfeeding or planning a pregnancy; is under 18; has kidney disease; or has a current or past eating disorder.

Shakiness, dizziness or confusion while on diabetes medicine can be low blood sugar happening now: the client follows their own treatment plan first, with emergency help if symptoms are severe or they cannot manage the episode, and tells the prescriber afterward (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). Refer promptly when constipation or other digestive trouble persists, or when the client is losing weight they did not intend to lose. Changes in eating, such as replacing more meals or skipping the ordinary meal, often have ordinary reasons. They become a referral concern when they come with distress, a narrowing of what the client eats, or interference with daily life; then the coach follows their own referral process or the client's existing care plan. A plan that replaces all food is a referral to a supervised program.

Special populations

Pregnancy and breastfeeding

One trial in 264 pregnant women with overweight or obesity found that a supervised program, which replaced 2 meals a day with products chosen by investigators to fit pregnancy needs alongside prenatal vitamins, reduced weight gain during pregnancy (Phelan et al., 2018). That was a research program with regular visits, delivered by staff with nutrition or health training, not a store-bought plan. The logged search for breastfeeding found no trial of partial meal replacement during breastfeeding. SlimFast's own plan page tells people who are pregnant or nursing to check with their doctor (SlimFast, 2024). Refer to the prenatal care team and a registered dietitian.

Children and adolescents

In a 12-month trial in 113 adolescents with obesity, a plan of 3 SlimFast shakes and 1 prepackaged meal a day within a lifestyle program led to a larger reduction in body mass index at 4 months than ordinary food, but no significant difference remained at 12 months (Berkowitz et al., 2011). NICE advises against a dietary approach alone for children and young people (National Institute for Health and Care Excellence, 2025), and SlimFast's plan page tells people under 18 to check with their doctor (SlimFast, 2024). Refer to the young person's pediatric care team.

Older adults

The logged search found only small, short studies in older adults. In one, 28 older adults with obesity completed 4 weeks of a once-daily meal replacement, comparing an experimental product enriched with essential amino acids with a commercial one (Coker et al., 2022). Losing muscle along with fat is a concern in older age, so an older client using meal replacements is referred to a physician or registered dietitian to check protein, strength and medicines.

Athletes and people with high activity

The logged search found one pilot study, in 8 elite handball players, of a high-protein bar formulated as a meal replacement and eaten after training for 5 days; it measured blood markers, not performance or health over time (Jovanov et al., 2021). Products built for weight loss supply fewer calories than a heavy training load may need; a sports dietitian is the right referral.

People taking medication for diabetes, blood pressure, or blood thinning

Insulin, sulfonylureas and meglitinides can cause low blood sugar, and eating fewer carbohydrates than usual can bring it on (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). Blood pressure fell in meal replacement trials in people with type 2 diabetes (Noronha et al., 2019). Warfarin's effect depends on steady vitamin K intake, and people taking it are told to talk to their doctor before changing their diet or adding vitamins or supplements (MedlinePlus, 2026); fortified shakes add vitamins every day. Glucerna's maker says to use it under medical supervision as part of a diabetes plan (Abbott, n.d.-c). The standing rule: the client keeps the prescriber informed before a change this size begins.

People with a history of disordered eating

The logged search found no study measuring eating disorder symptoms in people using partial meal replacements. The plans have features worth noticing: fixed portions, calorie targets, and a structure that can be extended by replacing more meals. In a pregnancy trial, the program increased dieting restraint (Phelan et al., 2018). For low-energy diets, NICE advises offering assessment and counseling to people who may have an eating disorder before starting (National Institute for Health and Care Excellence, 2025). The client's clinician is involved first, through the coach's own referral process or an existing care plan.

Client misconceptions

Three beliefs come up often. First, that shakes are a complete diet a person can live on: partial plans keep some ordinary food, and replacing all food is a supervised medical treatment (National Institute for Health and Care Excellence, 2025). Second, that meal replacements keep weight off for good: the longer trials show regain, with or without the products (Lowe et al., 2018). Third, that a diabetes shake treats diabetes: its maker says to use it under medical supervision as part of a diabetes plan (Abbott, n.d.-c), and SlimFast states that its products are not intended to treat or prevent disease (SlimFast, 2024). Section 6 gives each myth with its origin.

🤝 COACHING CONNECTION

Marisol tells her coach she has started 2 shakes a day because a coworker lost weight that way, and that lunch is easy but dinner with her kids is not. The coach asks what she hopes the shakes will make easier, and what dinner looks like on a good night. Marisol says she wants fewer decisions, not fewer family meals. The coach asks whether she takes any medicines; she mentions metformin and a pill for blood pressure. The coach asks how she would like to let her doctor know about the change, and Marisol decides to call her clinic before going further, and to plan 3 family dinners she already likes.

4. The evidence

(select the heading to open or close this section)

Most of the evidence on partial meal replacement comes from randomized trials of body weight lasting a year or less, many of them funded or supported by the companies that make the products. Together they suggest a modest extra weight loss at 1 year compared with ordinary-food diets with the same calorie target, rated very low in certainty here, and, over a few months, small reductions in blood pressure and LDL cholesterol and a trivial one in HbA1c in people with prediabetes or features of metabolic syndrome. The logged searches for this page found no trial isolating the products' effect on heart attacks, strokes, cancer or death, and the one long cohort study found links with higher death rates that cannot be read as cause and effect. The certainty ratings are in the Evidence rating and review record at the end of the page.

Evidence from randomized controlled trials

The largest review of partial replacement searched to August 2018 for randomized trials in adults with overweight or obesity that compared a plan including meal replacements with one that did not, and that reported weight at least 1 year after the start. It excluded diets under 800 calories a day and total replacement, and it included programs considered suitable for use in the community without medical supervision. It found 23 trials and grouped them into 5 comparisons by what each group received, from a meal replacement diet against the same diet with ordinary food, to whole commercial programs against minimal advice (Astbury et al., 2019). The review's figures for its total number of participants disagree with each other, so this page reports numbers by comparison only; the working files give the detail.

The review used the Cochrane risk of bias tool and did not grade the certainty of its results. It judged 6 of the 23 trials at low risk of bias in every domain and 5 at high risk in at least one, mostly because many more people dropped out of one group than the other; 17 trials did not report whether the allocation was concealed (Astbury et al., 2019). The certainty ratings on this page are therefore this page's own judgment, built from the review's data, with each GRADE domain recorded in the working files.

Checking the review's first comparison against the trials it cites showed 3 things a reader should know. In the German trial, randomization lasted 3 months; after that, both groups replaced 1 meal and 1 snack a day, so its later results compare an early start on meal replacements with a later one, not meal replacements with none (Ditschuneit et al., 1999). In an Australian trial of 31 men with diabetes, the meal replacement phase lasted 8 weeks, after which both groups followed the same high-protein diet (Khoo et al., 2011). And the abstract of a pharmacy-based trial describes a 3-month weight-loss phase and a 10-week maintenance phase and reports no 1-year result; its full report could not be checked (Ahrens et al., 2003). Only the abstracts of these 3 trials were opened.

Other reviews point the same way, with the same limits. A 2003 pooled analysis of 6 trials of liquid replacements found more weight loss with the partial plan at 3 months and at 1 year, about 7 to 8 percent of starting weight compared with 3 to 7 percent, depending on the analysis (Heymsfield et al., 2003). A 2021 review of 22 studies found a small advantage for low-energy diets built on meal replacements over food-based ones, and a larger one when replacements supplied at least 60 percent of daily energy (Min et al., 2021). Both were read as abstracts only. The 2013 US guideline for adults with overweight and obesity, read in its author manuscript, rated the evidence that meal replacements add weight loss at up to 6 months, in women, as low on its own scale, not GRADE, and judged longer-term evidence lacking (Jensen et al., 2014).

Cardiometabolic outcomes

In the 2019 review, results at 1 year consistently favored the meal replacement groups for HbA1c, a measure of average blood sugar, in the trials that reported it; results for fasting glucose, insulin, blood lipids and blood pressure were mixed and rarely reached statistical significance (Astbury et al., 2019). A 2019 review of 9 trial comparisons in 961 adults with type 2 diabetes, followed for a median of 24 weeks, found that liquid meal replacements within weight-loss diets lowered HbA1c by 0.43 percentage points (95 percent confidence interval 0.19 to 0.66) and systolic blood pressure by 4.97 mm Hg (2.62 to 7.32), with no effect found on blood lipids, compared with conventional weight-loss diets. Its authors judged the overall certainty low to moderate, using GRADE, because of imprecision or inconsistency (Noronha et al., 2019). Only its abstract could be opened, so this page does not carry its ratings.

A 2024 review by the same group, read in full, pooled 10 trials in 1,254 adults with prediabetes or features of metabolic syndrome, followed for a median of 12 weeks (range 6 to 52). Weight-loss programs that included meal replacements, which supplied a median 28 percent of daily energy, were compared with conventional food-based weight-loss diets. Systolic blood pressure fell 2.22 mm Hg more (0.23 to 4.20), LDL cholesterol 0.18 mmol/L more (0.08 to 0.28) and body weight 1.38 kilograms more (0.95 to 1.81). HbA1c fell 0.11 percentage points more, with an interval that reached zero (0.00 to 0.22). Against thresholds the authors set in advance, they called the blood pressure, cholesterol and weight changes small but important and the HbA1c change trivial (Noronha et al., 2024).

Using GRADE, the authors rated each of those 4 results moderate in certainty, lowered for imprecision; the review record carries their ratings for HbA1c, systolic blood pressure and LDL cholesterol. Those ratings are the review's own, for that population, comparison and short follow-up. They do not apply to people with type 2 diabetes, to longer use or to any one brand. Only 5 of the 10 trials reported information on adverse events (Noronha et al., 2024).

Look AHEAD, a trial of an intensive lifestyle program that included meal replacements, in 5,145 adults with type 2 diabetes, was stopped early for futility after a median of 9.6 years, with no reduction in cardiovascular events demonstrated, hazard ratio 0.95 (0.83 to 1.09) (Astbury et al., 2019; Look AHEAD Research Group, 2013). It tested the whole program, so it cannot say what the meal replacements did.

Cancer

The logged searches found no randomized trial of meal replacements that reported cancer incidence or cancer outcomes. The trials described here measured weight and risk markers over months to a few years, which cannot establish any effect on cancer in either direction.

Body weight, as measured

In the 2019 review's first comparison, 6 trials compared a meal replacement diet with the same kind of diet using ordinary food, without added support. At 1 year, the meal replacement groups (229 people) had changed by 3.0 kilograms on average and the ordinary-food groups (225 people) by 1.5 kilograms, a mean difference of 1.44 kilograms (0.39 to 2.48). At about 2 years, in 2 of those trials, the difference was 0.39 kilograms, with an interval from 2.07 kilograms more lost to 1.29 kilograms less, so no clear difference was detected. One trial reported a difference of 4.2 kilograms at 4 years, but it was the German trial in which both groups used meal replacements after the first 3 months (Astbury et al., 2019; Ditschuneit et al., 1999).

In the second comparison, 9 pooled trials compared a meal replacement diet plus a support program with an ordinary-food diet plus a similar support program. At 1 year, the meal replacement groups (622 people) had changed by 2.4 kilograms and the comparison groups (576 people) by 1.34 kilograms; the pooled difference, combined trial by trial, was 2.22 kilograms (0.45 to 3.99). Results varied widely between trials, which the review attributed to one small outlier. Two trials reported results at about 2 years (64 to 108 weeks), with a difference of 2.2 kilograms (0.38 to 4.02) that also varied between them (Astbury et al., 2019). The outlier the review cites is the Philadelphia trial described below, and the review's figures for it at 1 and 2 years do not match that trial's own published results, which this page could not resolve (Astbury et al., 2019; Lowe et al., 2018).

The other 3 comparisons tested whole programs, not the products alone. A meal replacement diet with support, compared with a diet alone, in 2 trials of commercial programs, those of Jenny Craig and Medifast, gave a difference of 3.87 kilograms (0.40 to 7.34); 2 trials of a Jenny Craig program with enhanced support, compared with a diet and support, gave 6.13 kilograms (4.91 to 7.35); and 3 trials against minimal intervention, including Look AHEAD, varied too much to pool (Astbury et al., 2019). Because the support differed between groups in these comparisons, they say more about the programs than about the products.

A 3-year trial in Philadelphia randomized 262 adults to behavioral treatment alone (90), behavioral treatment with meal replacements (91), or a program that changed the home food environment (81). The meal replacement group used 2 SlimFast products a day for 6 months, then 1 meal and 1 snack replacement, provided free for the treatment year. At 12 months, average losses were 9.41, 10.37 and 10.97 percent of starting weight; the meal replacement group did not differ significantly from either other group. All 3 groups regained, and at 36 months, when 69.5 percent of participants were assessed, losses were 4.21, 3.06 and 4.49 percent. The trial was funded by the National Institutes of Health (Lowe et al., 2018).

In a trial at 12 work sites, 335 employees with overweight or obesity were randomized by site to a wait-list or to a lifestyle program, and within program sites to the program with or without meal replacements. At 6 months, weight changed by 8.8 percent with the program alone and 8.0 percent with the program plus meal replacements, and no difference between the 2 was demonstrated (Das et al., 2023). In adolescents, a 12-month trial of 113 young people randomized 2 to 1 to meal replacements or ordinary food found a larger reduction in body mass index at 4 months with meal replacements, 6.3 compared with 3.8 percent, in the 65 and 37 analyzed at that point, but no significant difference at 12 months (Berkowitz et al., 2011).

In pregnancy, a trial at 2 sites randomized 264 women with overweight or obesity, at about 13 weeks of gestation, to enhanced usual care or a behavioral program that replaced 2 meals a day with products chosen by the investigators. Seven women withdrew after randomization and 1 was lost to follow-up, leaving 256 analyzed; the abstract reports 257 participants. The program group gained 0.33 kilograms a week compared with 0.39, a difference of 0.07 kilograms a week (0.02 to 0.13), and 41.1 percent compared with 53.9 percent exceeded the Institute of Medicine's guidelines for total gain. No significant effect was found on preterm birth, low birth weight, gestational diabetes, preeclampsia, cesarean delivery or high blood pressure, outcomes the trial was too small to judge (Phelan et al., 2018).

Mortality

The logged searches found no randomized trial designed to measure the effect of meal replacements on death. In Look AHEAD, cardiovascular death was part of the main outcome, for which no clear difference between groups was detected, but the trial tested a whole lifestyle program (Look AHEAD Research Group, 2013).

Eating behavior and wellbeing

Few trials measured eating behavior. In the pregnancy trial, the program increased dieting restraint and the use of weight-control strategies (Phelan et al., 2018), and both fell after delivery, along with meal replacement use, once the program ended (Phelan, Wing, et al., 2019). In a trial in adults with type 2 diabetes, read in abstract only, people in the meal replacement group rated the plan easier to follow (Cheskin et al., 2008). The logged search for eating disorders found no study measuring eating disorder symptoms in people using partial meal replacements.

Evidence from long-term prospective cohort studies

The logged searches found 1 prospective cohort analysis of meal replacement use and long-term outcomes. It used 6,770 adults aged 20 and older from the US National Health and Nutrition Examination Survey of 2003 to 2006, linked to death records through 2019, with a median follow-up of 14.4 years and 1,668 deaths. Use was measured once, by a food frequency question that asked how often people drank "meal replacement, energy, or high-protein beverages," with Instant Breakfast, Ensure, Slimfast and Sustacal as examples (Zhao et al., 2024). That question mixes weight-loss shakes with nutrition drinks often used by people who are ill or eating poorly, and it recorded nothing about type, amount, duration or reason.

Cardiometabolic outcomes

Compared with people who seldom drank these beverages, daily drinkers had a higher rate of death from cardiovascular disease, adjusted hazard ratio 1.70 (1.11 to 2.61); for weekly and monthly drinkers the intervals included no difference. When people with cardiovascular disease, diabetes or a special diet at the start were excluded, the association for daily drinkers was no longer statistically significant (Zhao et al., 2024).

Cancer

No association with cancer death was demonstrated: the adjusted hazard ratio for daily drinkers was 0.89 (0.43 to 1.83), with intervals including no difference for the other groups (Zhao et al., 2024).

Body weight, as measured

The logged searches found no prospective cohort study of meal replacement use and long-term body weight.

Mortality

Death from any cause was higher among people who drank these beverages monthly, weekly or daily than among those who seldom did, with adjusted hazard ratios of 1.26 (1.01 to 1.58), 1.54 (1.24 to 1.91) and 1.52 (1.17 to 1.97), and the association was stronger in women (Zhao et al., 2024). The authors concluded that frequent drinking "might increase" the risk. Because the exposure grouped very different drinks, was measured once, and could reflect illness that led people to drink them, the study shows an association, not that meal replacements shorten life. This page rates it Very low in the review record.

Highlighted studies

These 4 studies carry the most weight for this page: the main review of weight at 1 year, the longest trial with full follow-up reported, the one trial in a special population with full text, and the one cohort study of long-term outcomes.

On a narrow screen, scroll the table sideways to see every column.

Highlighted studies for Meal Replacement Programs

Study	Design	Sample size	Duration	Finding	The limitation that matters
Astbury et al., 2019	Systematic review and meta-analysis of randomized trials	23 trials; 454 people in the diet-only comparison and 1,198 in the comparison with support	1 year, with some 2-year and 4-year results	About 1.4 kilograms more weight lost at 1 year without added support and 2.2 kilograms with support, compared with ordinary-food diets	Some trials used meal replacements only briefly or let both groups use them later; dropout and industry funding were common; the review's figures for one trial do not match that trial's own report
Lowe et al., 2018	Randomized controlled trial, 3 groups	262 randomized; 69.5 percent assessed at 36 months	1 year of treatment, 3 years of follow-up	Meal replacements did not significantly change weight loss at 12 months compared with behavioral treatment alone; all groups regained by 36 months	Products were free for the treatment year, so it does not show what happens when people pay for them
Phelan et al., 2018	Randomized controlled trial in pregnancy	264 randomized; 256 analyzed	From about 13 weeks of gestation to 35 to 36 weeks	Weekly weight gain in pregnancy 0.07 kilograms lower with a supervised program that included partial meal replacement	A supervised research program; too small to judge birth outcomes
Zhao et al., 2024	Prospective cohort	6,770 adults	Median 14.4 years	Daily or weekly drinking of meal replacement, energy or high-protein beverages linked to about 50 percent higher death rates	The exposure question mixed weight-loss shakes with nutrition drinks for people who are ill; measured once

Head to head

Meal replacements have been compared with other structured approaches more than with named diets. In a 1-year trial, 96 women were randomized to a dietitian-led plan with 1 or 2 meal replacements a day or to the same plan with ordinary food; among the 70 who finished, weight change did not differ significantly, 5.0 compared with 6.1 kilograms (Ashley et al., 2007). In the Philadelphia trial, a program that changed the home food environment produced slightly larger average losses than meal replacements at 12 and 36 months, though that difference was not statistically significant (Lowe et al., 2018). In the work site trial, the same lifestyle program with and without meal replacements gave similar results at 6 months (Das et al., 2023).

Supervised formula programs that replace all food, whether under 800 calories a day or at about 800 to 1,200, are described on the Very Low Calorie Diets page. This page does not compare the commercial programs that rely on prepackaged meals or shakes, such as Jenny Craig, Nutrisystem and Optavia, one by one; the 2019 review's trials of Jenny Craig and Medifast programs are summarized above. WeightWatchers is a different kind of program, built on food tracking rather than replacement products. The logged searches found no trial comparing a partial meal replacement plan with the Diabetes Plate Method or with Mindful Eating.

Where the evidence is absent

Within the searches logged for this page, several gaps stand out. No trial isolated the effect of meal replacements on heart attacks, strokes, cancer or death. Few trials followed people for more than 2 years, and the longest follow-ups mixed groups or programs. Most trials provided the products free and paired them with regular contact, so self-directed use of store-bought products, the way most clients use them, has hardly been tested. The searches found no trial of partial meal replacement during breastfeeding, none of partial meal replacement in people with chronic kidney disease, none measuring eating disorder symptoms, and only small, short studies in older adults and athletes.

The logged searches found no study measuring the environmental footprint of the products, and the one modeling study of commercial diets consulted for this page did not include a meal replacement plan (Neff et al., 2023). The 2019 review found no information on costs to individuals (Astbury et al., 2019). The products tested in trials published between 1999 and 2018 may also differ from those on the market in 2026.

5. Mechanisms

(optional reading; select the heading to open or close this section)

This section explains how the diet is thought to work in the body. You can skip it. Nothing in the coaching sections depends on it.

Established mechanisms

Meal replacements do not work through a special ingredient. In the trials, both groups were usually given the same calorie target, and the products were one way of meeting it (Heymsfield et al., 2003; Ditschuneit et al., 1999). The weight lost follows from eating fewer calories than the body uses, an energy deficit; what the trials test is whether a printed, fixed portion helps people stay closer to that target than choosing and estimating their own portions. The other effect shown in people is nutritional: in 2 trials, adding fortified products raised intake of several vitamins and minerals, such as calcium and vitamins A, D and E, compared with the comparison groups (Ashley et al., 2007; Phelan, Abrams, & Wing, 2019).

Proposed mechanisms

Several explanations are plausible but have not been tested as causes. Fewer food decisions may make a plan easier to follow, which fits the finding that people rated a meal replacement plan easier (Cheskin et al., 2008), though that rating does not show why. A common proposal, not tested in these trials, is that protein helps people feel full; products differ widely in protein, from 10 to 12 grams in a Glucerna shake to 40 grams in a Huel Black Edition meal (Abbott, n.d.-b; Huel, n.d.). Abbott describes Glucerna as made with slow-release carbohydrates to help manage the rise in blood sugar after drinking it (Abbott, n.d.-b). The authors of the cohort study suggested that processing or high protein intake might explain the link with higher death rates (Zhao et al., 2024). These are proposals, labeled as such, and none of them supports a claim in section 4.

6. Risks, contraindications and myths

(select the heading to open or close this section)

Warnings from professional or regulatory bodies

NICE, which writes clinical guidelines for England, advises considering low-energy diets of 800 to 1,200 calories a day only as part of a strategy with long-term support within a specialist weight management service, or a service for a long-term condition such as type 2 diabetes, and states: "Do not use low-energy diets or very-low-energy diets as a long-term strategy to manage obesity." It adds that such diets should be nutritionally complete and last no more than 12 weeks (National Institute for Health and Care Excellence, 2025).

That definition is about the day's total calories, not about whether a plan replaces some meals or all of them. SlimFast's plan for women, about 1,200 to 1,300 calories a day, reaches the top of NICE's range at 1,200 and is above it at 1,300, and its plan for men, about 1,500, is above it (SlimFast, 2024). A plan can keep an ordinary meal and still fall well inside the range: in a trial of the Medifast 5 & 1 plan, 5 replacements a day plus 1 self-selected meal were described as 800 to 1,000 calories a day (Astbury et al., 2019). The American Diabetes Association lists "meal replacement plans prescribed by trained professionals" among common approaches to weight loss in diabetes (American Diabetes Association Professional Practice Committee for Diabetes, 2026).

The companies carry their own cautions. Abbott says: "Use Glucerna under medical supervision as part of your diabetes management plan" (Abbott, n.d.-c). SlimFast states that its product is "not intended for the treatment or prevention of disease," and asks people to check with their doctor if they have type 1, type 2 or gestational diabetes, are insulin dependent, nursing, pregnant, under 18, or following a diet a doctor prescribed (SlimFast, 2024).

Nutrient gaps

Fortified products can close some gaps rather than open them: in 2 trials, intake of several vitamins and minerals was better with meal replacements than in the comparison groups (Ashley et al., 2007; Phelan, Abrams, & Wing, 2019). What the rest of the day supplies still matters, and products differ widely. Huel lists 40 grams of protein and up to 11 grams of fiber in a 400-calorie Black Edition meal (Huel, n.d.); Abbott lists 10 to 12 grams of protein and 140 to 180 calories in a Glucerna shake (Abbott, n.d.-b). A shake of 140 calories in place of a full meal can leave a person short on energy and protein if the ordinary meals do not make it up. A product sold as plant-based raises the same questions as any vegan food; the Vegan Diet page covers them.

Side effects were rarely reported in the weight-loss trials: only 2 of 23 trials in the 2019 review reported adverse events, and they found no excess with meal replacements (Astbury et al., 2019). A scoping review of 133 studies of meal replacements in type 2 diabetes found that 13 reported adverse events, most of them mild, with constipation the one reported most often (Lew et al., 2025).

Who should not follow it without medical supervision

People taking insulin, sulfonylureas or meglitinides, because eating fewer carbohydrates can bring on low blood sugar (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). People taking blood pressure medicines, since blood pressure fell in trials (Noronha et al., 2019), and people taking warfarin (MedlinePlus, 2026). People who are pregnant or breastfeeding, and anyone under 18 (SlimFast, 2024; National Institute for Health and Care Excellence, 2025). People with kidney disease, whose protein and mineral needs depend on the stage of the disease, their lab results and whether they are on dialysis, which the kidney care team decides; a high-protein shake is a decision for that team. People with a current or past eating disorder (National Institute for Health and Care Excellence, 2025). Older adults at risk of muscle loss (Coker et al., 2022).

Medication interactions

A coach never adjusts medication. The point of knowing these is to know when to send a client back to the prescriber. Insulin, sulfonylureas and meglitinides can cause low blood sugar, and eating fewer carbohydrates than usual can bring it on (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). Blood pressure medicines may need review as blood pressure falls (Noronha et al., 2019). Warfarin's effect depends on steady vitamin K intake, and its patient information asks people to tell their doctor and pharmacist about vitamins and nutritional supplements and to talk to their doctor before changing their diet (MedlinePlus, 2026); a fortified shake taken every day is that kind of change. The standing rule is that the client keeps the prescriber informed before a change of this size begins.

Signs it is going wrong

Some signs need the client's care plan, a clinician or emergency help. Shakiness, hunger, dizziness, confusion or a racing heart in someone taking insulin or a sulfonylurea may be low blood sugar happening now. The first step is the one in the person's own diabetes plan, with emergency help if symptoms are severe or the person cannot manage the episode; telling the prescriber is the separate step that follows (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.). Constipation or digestive trouble that persists, ongoing tiredness, or dizziness on standing are reasons to see a clinician. Weight a client loses without meaning to, for example because shakes have quietly replaced more meals than planned, is also a reason to involve a clinician; it is never a goal or a sign the plan is working.

Eating behaviors are a separate matter, and on their own they say little. Replacing an extra meal, skipping the ordinary meal or eating the same thing every day can have ordinary explanations, such as a busy work schedule, food access, a household's preferences or a cultural practice, and none of this is a diagnosis. The coach asks what the behavior is for, whether it causes distress, whether it is narrowing what the person eats, and whether it is getting in the way of daily life. Where the answers raise a real concern about disordered eating, the coach follows their own referral process, or brings the concern to the client's clinician under an existing care plan.

Myths and where they came from

Myth: "Shakes are a complete diet, so I can live on them."

Where it came from: products are sold as complete nutrition, such as Huel's complete meal with all 27 essential vitamins and minerals (Huel, n.d.), and total replacement programs exist. What is true: partial plans keep some ordinary food, as SlimFast's plan does with 1 meal of the person's choosing (SlimFast, 2024), and replacing all food is a supervised medical treatment. NICE limits low-energy and very-low-energy diets, whatever their form, to specialist or long-term-condition services and to no more than 12 weeks (National Institute for Health and Care Excellence, 2025).

Myth: "Meal replacements keep the weight off for good."

Where it came from: company marketing that promises sustainable weight loss (SlimFast, 2024) and short trials that showed early advantages. What is true: at 2 years no clear difference was detected in the trials without added support, and in a 3-year trial people regained much of what they had lost, with or without meal replacements (Astbury et al., 2019; Lowe et al., 2018).

Myth: "A diabetes shake treats my diabetes."

Where it came from: products designed and named for people with diabetes, marketed to help manage blood sugar response (Abbott, n.d.-c). What is true: in trials, liquid replacements within weight-loss diets lowered HbA1c by a small amount (Noronha et al., 2019), and Abbott itself says to use Glucerna under medical supervision as part of a diabetes plan (Abbott, n.d.-c).

Myth: "Meal replacement drinks shorten your life."

Where it came from: a 2024 cohort study that linked frequent drinking of meal replacement, energy or high-protein beverages with higher death rates (Zhao et al., 2024). What is true: that study grouped weight-loss shakes with nutrition drinks often used by people who are ill and measured use once, so it shows an association, not a cause; this page rates it Very low.

7. Key terms

Meal replacement

A shake, bar or packaged meal with a set number of calories, usually fortified with vitamins and minerals, eaten in place of an ordinary meal.

Partial meal replacement

A plan that replaces one or more meals a day, most often 1 or 2, and keeps some ordinary food. It can still be low in total calories.

Total diet replacement

A plan in which formula products are the only food for a set number of weeks, used under medical supervision. It is defined by replacing the whole diet, not by a calorie number.

Low-energy diet

A diet of about 800 to 1,200 calories a day, as NICE defines it. The definition is about the day's total, so a partial plan can fall inside it.

Diabetes-specific formula

A shake or bar designed for people with diabetes, usually with carbohydrates meant to raise blood sugar more slowly.

Energy deficit

Eating fewer calories than the body uses, which is what produces weight loss on any reduced-calorie plan.

Mean difference

The average result in one group minus the average in the other, here in kilograms of body weight.

Risk of bias

The chance that a study's design or conduct, such as many people dropping out of one group, has distorted its result.

Reverse causation

When an apparent cause is really a result, as when illness leads people to drink nutrition shakes rather than the shakes causing illness.

Gestational weight gain

The weight a person gains during pregnancy, measured in studies to compare with recommended ranges.

Hypoglycemia

Low blood sugar, which can be caused by some diabetes medicines when a person eats less than usual.

8. Review questions

1. How does a partial meal replacement plan differ from total diet replacement, and why is that a separate question from how many calories a plan supplies?
2. In the 2019 review, what was compared in the first and second comparisons, how large was the difference in weight at 1 year, and why does this page rate the certainty of both results very low?
3. In the 3-year Philadelphia trial, what happened to weight in all 3 groups between 12 and 36 months, and what does that suggest a client should plan for?
4. A client taking insulin tells you she has replaced breakfast and lunch with shakes and feels shaky in the afternoons. What happens first, and where is the referral line?
5. Where does the belief that meal replacement drinks shorten life come from, and what would a study need to show to support it?

9. References

Abbott. (n.d.-a). Glucerna products on AbbottStore. Retrieved October 11, 2026, from abbottstore.com/diabetes-management/​glucerna.html

Abbott. (n.d.-b). Glucerna original: Rich chocolate diabetic shake. glucerna.com/nutrition-products/​glucerna-shakes-rich-chocolate

Abbott. (n.d.-c). Why choose Glucerna for diabetes and blood sugar management? glucerna.com/why-glucerna

Ahrens, R. A., Hower, M., & Best, A. M. (2003). Effects of weight reduction interventions by community pharmacists. Journal of the American Pharmacists Association, 43(5), 583-589. https://doi.org/10.1331/154434503322452210

American Diabetes Association Professional Practice Committee for Diabetes. (2026). 8. Obesity and weight management for the prevention and treatment of diabetes: Standards of Care in Diabetes-2026. Diabetes Care, 49(Suppl. 1), S166-S182. https://doi.org/10.2337/dc26-S008

Ashley, J. M., Herzog, H., Clodfelter, S., Bovee, V., Schrage, J., & Pritsos, C. (2007). Nutrient adequacy during weight loss interventions: A randomized study in women comparing the dietary intake in a meal replacement group with a traditional food group. Nutrition Journal, 6, Article 12. https://doi.org/10.1186/1475-2891-6-12

Ashley, J. M., St Jeor, S. T., Perumean-Chaney, S., Schrage, J., & Bovee, V. (2001). Meal replacements in weight intervention. Obesity Research, 9(Suppl. 4), 312S-320S. https://doi.org/10.1038/oby.2001.136

Astbury, N. M., Piernas, C., Hartmann-Boyce, J., Lapworth, S., Aveyard, P., & Jebb, S. A. (2019). A systematic review and meta-analysis of the effectiveness of meal replacements for weight loss. Obesity Reviews, 20(4), 569-587. https://doi.org/10.1111/obr.12816

Berkowitz, R. I., Wadden, T. A., Gehrman, C. A., Bishop-Gilyard, C. T., Moore, R. H., Womble, L. G., Cronquist, J. L., Trumpikas, N. L., Levitt Katz, L. E., & Xanthopoulos, M. S. (2011). Meal replacements in the treatment of adolescent obesity: A randomized controlled trial. Obesity, 19(6), 1193-1199. https://doi.org/10.1038/oby.2010.288

Cheskin, L. J., Mitchell, A. M., Jhaveri, A. D., Mitola, A. H., Davis, L. M., Lewis, R. A., Yep, M. A., & Lycan, T. W. (2008). Efficacy of meal replacements versus a standard food-based diet for weight loss in type 2 diabetes: A controlled clinical trial. The Diabetes Educator, 34(1), 118-127. https://doi.org/10.1177/0145721707312463

Coker, M. S., Barati, Z., Murphy, C. J., Bateman, T., Newcomer, B. R., Wolfe, R. R., & Coker, R. H. (2022). Essential amino acid enriched meal replacement improves body composition and physical function in obese older adults: A randomized controlled trial. Clinical Nutrition ESPEN, 51, 104-111. https://doi.org/10.1016/j.clnesp.2022.07.004

Das, S. K., Silver, R. E., Vail, T. A., Chin, M. K., Blanchard, C. M., Dickinson, S. L., Chen, X., Ceglia, L., Saltzman, E., Allison, D. B., & Roberts, S. B. (2023). Randomized controlled trial of a novel lifestyle intervention used with or without meal replacements in work sites. Obesity, 31(2), 374-389. https://doi.org/10.1002/oby.23636

Ditschuneit, H. H., Flechtner-Mors, M., Johnson, T. D., & Adler, G. (1999). Metabolic and weight-loss effects of a long-term dietary intervention in obese patients. The American Journal of Clinical Nutrition, 69(2), 198-204. https://doi.org/10.1093/ajcn/69.2.198

Heymsfield, S. B., van Mierlo, C. A., van der Knaap, H. C., Heo, M., & Frier, H. I. (2003). Weight management using a meal replacement strategy: Meta and pooling analysis from six studies. International Journal of Obesity and Related Metabolic Disorders, 27(5), 537-549. https://doi.org/10.1038/sj.ijo.0802258

Huel. (n.d.). Black Edition: Meal replacement protein powder. Retrieved October 11, 2026, from huel.com/products/huel-black-edition

Jensen, M. D., Ryan, D. H., Apovian, C. M., Ard, J. D., Comuzzie, A. G., Donato, K. A., Hu, F. B., Hubbard, V. S., Jakicic, J. M., Kushner, R. F., Loria, C. M., Millen, B. E., Nonas, C. A., Pi-Sunyer, F. X., Stevens, J., Stevens, V. J., Wadden, T. A., Wolfe, B. M., & Yanovski, S. Z. (2014). 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and The Obesity Society. Circulation, 129(25 Suppl. 2), S102-S138. https://doi.org/10.1161/01.cir.0000437739.71477.ee

Jovanov, P., Sakač, M., Jurdana, M., Pražnikar, Z. J., Kenig, S., Hadnađev, M., Jakus, T., Petelin, A., Škrobot, D., & Marić, A. (2021). High-protein bar as a meal replacement in elite sports nutrition: A pilot study. Foods, 10(11), Article 2628. https://doi.org/10.3390/foods10112628

Khoo, J., Piantadosi, C., Duncan, R., Worthley, S. G., Jenkins, A., Noakes, M., Worthley, M. I., Lange, K., & Wittert, G. A. (2011). Comparing effects of a low-energy diet and a high-protein low-fat diet on sexual and endothelial function, urinary tract symptoms, and inflammation in obese diabetic men. The Journal of Sexual Medicine, 8(10), 2868-2875. https://doi.org/10.1111/j.1743-6109.2011.02417.x

Lew, L. C., Mat Ludin, A. F., Abdul Manaf, Z., Mohd Tohit, N., & Shahar, S. (2025). Mapping evidence and identifying risks: A systematic scoping review of meal replacements in type 2 diabetes. World Journal of Diabetes, 16(8), Article 104371. https://doi.org/10.4239/wjd.v16.i8.104371

Look AHEAD Research Group. (2013). Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes. The New England Journal of Medicine, 369(2), 145-154. https://doi.org/10.1056/NEJMoa1212914

Lowe, M. R., Butryn, M. L., & Zhang, F. (2018). Evaluation of meal replacements and a home food environment intervention for long-term weight loss: A randomized controlled trial. The American Journal of Clinical Nutrition, 107(1), 12-19. https://doi.org/10.1093/ajcn/nqx005

Maston, G., Franklin, J., Gibson, A. A., Manson, E., Hocking, S., Sainsbury, A., & Markovic, T. P. (2020). Attitudes and approaches to use of meal replacement products among healthcare professionals in management of excess weight. Behavioral Sciences, 10(9), Article 136. https://doi.org/10.3390/bs10090136

MedlinePlus. (2026, March 15). Warfarin. National Library of Medicine. medlineplus.gov/druginfo/meds/a682277.html

Min, J., Kim, S. Y., Shin, I. S., Park, Y. B., & Lim, Y. W. (2021). The effect of meal replacement on weight loss according to calorie-restriction type and proportion of energy intake: A systematic review and meta-analysis of randomized controlled trials. Journal of the Academy of Nutrition and Dietetics, 121(8), 1551-1564.e3. https://doi.org/10.1016/j.jand.2021.05.001

National Institute for Health and Care Excellence. (2025). Overweight and obesity management (NICE Guideline NG246; last updated January 8, 2026). nice.org.uk/guidance/ng246/chapter/​Physical-activity-and-diet

National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.). Low blood glucose (hypoglycemia). National Institutes of Health. niddk.nih.gov/health-information/diabetes/overview/​preventing-problems/low-blood-glucose-hypoglycemia

Neff, R. A., Ramsing, R. J., & Kim, B. F. (2023). Commercial weight-loss diets, greenhouse gas emissions and freshwater consumption. Journal of Human Nutrition and Dietetics, 36(6), 2268-2279. https://doi.org/10.1111/jhn.13248

Noronha, J. C., Nishi, S. K., Braunstein, C. R., Khan, T. A., Blanco Mejia, S., Kendall, C. W. C., Kahleová, H., Rahelić, D., Salas-Salvadó, J., Leiter, L. A., & Sievenpiper, J. L. (2019). The effect of liquid meal replacements on cardiometabolic risk factors in overweight/obese individuals with type 2 diabetes: A systematic review and meta-analysis of randomized controlled trials. Diabetes Care, 42(5), 767-776. https://doi.org/10.2337/dc18-2270

Noronha, J. C., Nishi, S. K., Khan, T. A., Blanco Mejia, S., Kendall, C. W. C., Kahleová, H., Rahelić, D., Salas-Salvadó, J., Leiter, L. A., Lean, M. E. J., & Sievenpiper, J. L. (2024). Weight management using meal replacements and cardiometabolic risk reduction in individuals with pre-diabetes and features of metabolic syndrome: A systematic review and meta-analysis of randomized controlled trials. Obesity Reviews, 25(7), Article e13751. https://doi.org/10.1111/obr.13751

Phelan, S., Abrams, B., & Wing, R. R. (2019). Prenatal intervention with partial meal replacement improves micronutrient intake of pregnant women with obesity. Nutrients, 11(5), Article 1071. https://doi.org/10.3390/nu11051071

Phelan, S., Wing, R. R., Brannen, A., McHugh, A., Hagobian, T. A., Schaffner, A., Jelalian, E., Hart, C. N., Scholl, T. O., Munoz-Christian, K., Yin, E., Phipps, M. G., Keadle, S., & Abrams, B. (2018). Randomized controlled clinical trial of behavioral lifestyle intervention with partial meal replacement to reduce excessive gestational weight gain. The American Journal of Clinical Nutrition, 107(2), 183-194. https://doi.org/10.1093/ajcn/nqx043

Phelan, S., Wing, R. R., Brannen, A., McHugh, A., Hagobian, T., Schaffner, A., Jelalian, E., Hart, C. N., Scholl, T. O., Muñoz-Christian, K., Yin, E., Phipps, M. G., Keadle, S., & Abrams, B. (2019). Does partial meal replacement during pregnancy reduce 12-month postpartum weight retention? Obesity, 27(2), 226-236. https://doi.org/10.1002/oby.22361

SlimFast. (2024, May 22). The SlimFast plan: How it works. slimfast.com/food-nutrition/​the-slimfast-plan-how-it-works

Zhao, Y., Li, A., Yang, H., Xiao, M., Song, M., Shao, Z., Jiao, R., Pang, Y., Gao, W., Huang, T., Lv, J., Li, L., Yu, C., & Sun, D. (2024). The frequency of meal-replacement products drinking and all-cause, CVD, and cancer mortality. Nutrients, 16(21), Article 3770. https://doi.org/10.3390/nu16213770

Evidence rating and review record

Each row identifies the method, source, outcome or recommendation, and comparison being rated. Ratings from different tools are not interchangeable. The source is either a named published review or this page's own judgment. The rating in the banner is for this diet's main claimed outcome or recommendation, and the banner names the tool that produced it. A high rating means the research is solid; it does not mean the diet is right for everyone, and it does not mean a coach should recommend it.

Rows rated with GRADE use the same 4-level scale as the clinical guidelines you will meet in practice. High means further research is very unlikely to change the conclusion. Moderate means further research may change it. Low means further research is likely to change it. Very low means the conclusion is uncertain. GRADE rates each outcome separately, so a diet can be high for one outcome and very low for another.

Most GRADE ratings on this page are this page's own judgment, assigned from the evidence with each GRADE domain recorded in the working files. Three rows carry the published GRADE judgments of the 2024 review by Noronha and colleagues, read in full, exactly as that review gave them and named as its own. The 2019 review by the same group could be read only in abstract, so its ratings are not carried. For imprecision, this page treats a difference of 1 kilogram in body weight at 1 year or later as the smallest difference worth noticing, and, for weight gain in pregnancy, 0.05 kilograms a week, about 1 kilogram over the 22 to 23 weeks the pregnancy trial measured. These are judgments stated so that readers can disagree with them.

On a narrow screen, scroll the table sideways to see every column.

Evidence ratings, their sources and reasons

Outcome	Certainty	Who rated it, and for which comparison	Why it is rated this way
Body weight at 1 year, as measured, with support: the main outcome and the first rating in the banner	Very low	GRADE, this page's own judgment, from the data of Astbury et al. (2019). A meal replacement diet plus a support program, compared with an ordinary-food diet plus a similar support program, in adults with overweight or obesity, in 9 pooled randomized trials of 1,198 people, at 1 year	Randomized trials start high; lowered 3 levels, to very low. Lowered 1 level for risk of bias: the review's table judged 3 of these trials at high risk of bias for incomplete outcome data, and most did not report allocation concealment. Lowered 1 level for inconsistency: the results varied widely between trials (I squared 81 percent), and the review's figures for the trial it names as the outlier do not match that trial's own report. Lowered 1 level for imprecision, a separate problem from the variation between trials: the interval, 0.45 to 3.99 kilograms, runs from below the 1-kilogram threshold to well above it, and a recalculation from the review's own figure without the outlier still crosses the threshold. Indirectness not lowered: the populations and the matched-support comparison fit the question; in one arm of one trial the support differed, and that arm carries little weight. Publication bias not lowered, although industry funding was common and the review could not rule it out. No reason to raise the rating. Weight is reported as a measurement, not a goal
Body weight at 1 year, as measured, without added support: the second rating in the banner	Very low	GRADE, this page's own judgment, from the data of Astbury et al. (2019). A meal replacement diet compared with an ordinary-food diet, without added support in either group, in adults with overweight or obesity, in 6 randomized trials of 454 people, at 1 year	Starts high. Lowered 1 level for risk of bias: the review's table judged 2 of the 6 trials at high risk of bias for incomplete outcome data, and 5 did not report allocation concealment. Lowered 1 level for indirectness: in 2 trials the meal replacement phase lasted only 8 weeks or 3 months, and in one of them both groups used meal replacements afterward, so these trials do not compare meal replacements with none at 1 year; the abstract of a third reports no 1-year result. Lowered 1 level for imprecision: the interval, 0.39 to 2.48 kilograms, includes differences below the 1-kilogram threshold. Inconsistency not lowered (I squared 38 percent). Publication bias not lowered, with the same caution as above. No reason to raise the rating
Body weight at 2 years, as measured, without added support	Very low	GRADE, this page's own judgment, from the data of Astbury et al. (2019). The same comparison as the row above, in the 2 trials with results at about 2 years, 148 people: the German trial and a trial in adults with type 2 diabetes measured at 86 weeks (the review's 2-year results span 64 to 108 weeks)	Starts high. Lowered 2 levels for imprecision: 148 people, and an interval from 2.07 kilograms more lost to 1.29 kilograms less, which includes no difference and differences in both directions. Risk of bias: the review judged the diabetes trial at high risk for incomplete outcome data. Indirectness: in the German trial both groups used meal replacements after the first 3 months, so it does not compare meal replacements with none at 2 years. Either would lower the rating further, and it is already at its floor. Inconsistency not lowered (I squared 0 percent, though 2 trials cannot show that the effects are the same). Publication bias cannot be judged with 2 trials. No reason to raise the rating. This rating means the 2-year difference is uncertain; it is not evidence that there is none
Body weight at 2 years, as measured, with support	Very low	GRADE, this page's own judgment, from the data of Astbury et al. (2019). The comparison in the first row, at about 2 years, in 2 trials and 294 people in the review's figure: an earlier SlimFast-funded trial in premenopausal women, entered as 2 meal replacement arms that shared one comparison group (Ashley et al., 2001, read in abstract only), and the Philadelphia trial (Lowe et al., 2018)	Starts high. Lowered 1 level for risk of bias: neither trial reported how allocation was concealed; in the earlier trial only 43 of 113 women completed the second year, according to its abstract; and the review's 2-year figures for the Philadelphia trial do not match that trial's own report, in which the meal replacement group had lost slightly less than behavioral treatment alone at 24 months. Lowered 1 level for inconsistency: the results differed (I squared 67 percent). Lowered 1 level for imprecision: an interval of 0.38 to 4.02 kilograms, which includes differences below the 1-kilogram threshold. Indirectness: in one arm the meal replacement group had brief office visits while the comparison group had dietitian-led classes, so support was not matched there; not counted further, since the rating is at its floor. Publication bias cannot be judged with 2 trials. No reason to raise the rating
Weight gain during pregnancy, as measured, with a supervised program	Moderate	GRADE, this page's own judgment, from Phelan et al. (2018), read in full. A behavioral program with partial meal replacement, supervised by research staff, compared with enhanced usual care, in 264 randomized pregnant women with overweight or obesity, from about 13 weeks to 35 to 36 weeks of gestation	Starts high. Risk of bias not lowered: randomization was computer-generated by the study statistician, weight was measured in duplicate by staff masked to the group, and 256 of 264 were analyzed; the paper does not describe how allocation was concealed, and participants knew their group, which matters less for a measured weight. Inconsistency cannot be judged with 1 trial and is not a reason to lower. Indirectness not lowered for the program the row rates; the row does not apply to self-directed use or to any restriction a person plans on their own in pregnancy. Lowered 1 level for imprecision: the interval, 0.02 to 0.13 kilograms a week, runs from below this page's 0.05-kilogram threshold to above it, in a single trial. Publication bias cannot be judged. No reason to raise the rating. Birth outcomes are not rated: the trial was too small to judge them
HbA1c in adults with prediabetes or features of metabolic syndrome, over a median of 12 weeks	Moderate	GRADE, the published judgment of Noronha et al. (2024), read in full, not this page's. Weight-loss programs that included meal replacements, compared with conventional food-based weight-loss diets, in adults with prediabetes or features of metabolic syndrome, in 7 randomized trials of 600 people, followed for a median of 12 weeks across the review (range 6 to 52)	The review started randomized trials high and lowered this result 1 level for imprecision, with no deduction for risk of bias, inconsistency, indirectness or publication bias. The difference was 0.11 percentage points (0.00 to 0.22), below the review's 0.3-point threshold, so the review called it trivial: moderate certainty in a very small effect, not in a meaningful benefit
Systolic blood pressure in adults with prediabetes or features of metabolic syndrome, over a median of 12 weeks	Moderate	GRADE, the published judgment of Noronha et al. (2024), read in full, not this page's. Weight-loss programs that included meal replacements, compared with conventional food-based weight-loss diets, in adults with prediabetes or features of metabolic syndrome, in 9 randomized trials of 1,061 people, followed for a median of 12 weeks across the review (range 6 to 52)	The review started randomized trials high and lowered this result 1 level for imprecision, with no deduction for risk of bias, inconsistency, indirectness or publication bias. The difference was 2.22 mm Hg (0.23 to 4.20). The review called it small but important against its 2 mm Hg threshold; the interval also includes much smaller changes
LDL cholesterol in adults with prediabetes or features of metabolic syndrome, over a median of 12 weeks	Moderate	GRADE, the published judgment of Noronha et al. (2024), read in full, not this page's. Weight-loss programs that included meal replacements, compared with conventional food-based weight-loss diets, in adults with prediabetes or features of metabolic syndrome, in 7 randomized trials of 937 people, followed for a median of 12 weeks across the review (range 6 to 52)	The review started randomized trials high and lowered this result 1 level for imprecision, with no deduction for risk of bias, inconsistency, indirectness or publication bias. The difference was 0.18 mmol/L (0.08 to 0.28). The review called it small but important against its 0.1 mmol/L threshold; the interval also includes changes below that threshold
HbA1c, blood pressure and blood lipids in adults with type 2 diabetes	Not rated	Not rated by this page. Noronha et al. (2019) rated these outcomes with GRADE, but only its abstract could be opened, and the abstract gives an overall label of low to moderate across outcomes, not a label for each	A published rating is carried only outcome by outcome and only when the source is read, so this page does not carry the abstract's overall label or assign its own. The 2024 ratings in the rows above do not transfer to this population
Death from any cause, associated with frequent drinking of meal replacement, energy or high-protein beverages	Very low	GRADE, this page's own judgment, from Zhao et al. (2024), read in full. Daily, weekly or monthly drinking compared with seldom drinking, in 6,770 US adults followed for a median of 14.4 years	Observational evidence starts low. Lowered 1 level for risk of bias: use was measured once by self-report, and confounding by illness and reverse causation are likely, since the drinks include nutrition products used by people who are ill; sensitivity analyses addressed this only in part. Lowered 1 level for indirectness: the exposure grouped weight-loss shakes with energy and high-protein drinks and recorded no type, amount or reason. Not raised for the size of the association. Inconsistency not assessable with 1 study; imprecision and publication bias not lowered further, since the rating is at its floor
Heart attacks, strokes and death	Not rated	Not rated by this page. The logged searches found no randomized trial that isolated the effect of meal replacements on these outcomes	Look AHEAD measured cardiovascular events and deaths but tested a whole lifestyle program that included meal replacements, and found no reduction; it cannot show what the products did
Eating disorder symptoms	Not rated	Not rated by this page. The logged search found no study measuring eating disorder symptoms in people using partial meal replacements	With no study, there is nothing to rate. This is a gap in the evidence, not evidence of safety

How this archive talks about weight. This page reports what studies measured, including body weight, and does not treat weight change as a goal or as a measure of a diet's success. Weight a person loses without meaning to can be a sign of a health problem, and where it is, the page names it as a reason to see a clinician. People are described the way the study described them.

Last reviewed: Reviewed and approved by James Peth, MS, MPH, PhD, on October 11, 2026, after a combined final review of the fourth batch of 5 archive pages, the commercial programs, the repairs it asked for and a targeted recheck. Written October 11, 2026. The judgments in the table, apart from the 3 rows carried from a published review, are this page's own, assigned from the evidence. Some sources could be read only as abstracts or author manuscripts, and the page says so where each is used. Company prices and terms are a snapshot from the company's own pages on October 11, 2026, and can change.

Next scheduled review: August 2027. Pages built on annual guidance are rechecked each year. The American Diabetes Association's Standards of Care, updated every year, the NICE guideline, and the companies' prices and product claims are in that category and should be rechecked first.

---

Diet Reference Archive | One James

Prepared by James Peth, MS, MPH, PhD

© 2026–2027 One James. All rights reserved.

This page is for education and coaching practice. It is not medical or dietary advice.