Do commercial weight loss programmes actually work?

Against standard family doctor care, yes, and this is the strongest head-to-head evidence any consumer diet product on this site has. Referral to a commercial program led to 5.06 kg lost against 2.25 kg on standard care at twelve months, and a 52-week referral led to 6.76 kg lost against 3.26 kg on brief advice. An independent review of 45 studies put the twelve-month edge at at least 2.6 percent of body weight for the group program and at least 4.9 percent for the prepared-meal one.

Who paid for those trials?

Mostly the company being tested. The two largest European studies were paid for by Weight Watchers International, in both cases through the UK Medical Research Council. That is disclosed in the papers, and it belongs in any honest reading of them. It also cuts both ways. The industry-funded studies published their high dropout rates and a cost per kilogram, and the review that declares no funding reached a favourable view of the same program.

Does the weight stay off?

Partly, for as long as anyone has looked, which is two years. The two-year comparison against self-help finished at 2.9 against 0.2 kg lost, down from 4.3 at one year. The prepared-meal study finished 7.4 kg down at 24 months. The very low calorie medical programs are the exception both ways: 15 to 25 percent loss in people who finished, and a high chance of regaining half or more within one to two years.

Is one programme better than another?

Not in the direct comparison. Four commercial programs run head to head for six months all beat the comparison group and did not really differ from each other, averaging 5.9 kg lost. In a review that pooled 48 trials, the differences between named diets were tiny, while behaviour support added 3.23 kg at six months. The structure seems to be what works, not the brand.

Two studies tested it. In prediabetes, twelve months led to 5.5 percent weight loss, against 0.2 percent on a national education program, with better long-term blood sugar and HDL. In type 2 diabetes, long-term blood sugar fell 0.32 points against a 0.16 rise, 24 against 14 percent got it below 7.0, and 26 against 12 percent cut back their diabetes medicines. That last figure is why anyone on insulin or a sulfonylurea should tell their prescriber before joining.

Macronutrient-defined8 studies in people cited

Commercial weight loss programmes

Written by Aaron CuhaReviewed Sep 2026

Also called: WW, Weight Watchers, Jenny Craig, Nutrisystem, Slimming World

The best-tested consumer diet product on this site, for an unglamorous reason: these are the only diets whose owners paid for head-to-head trials. Being referred by a family doctor roughly doubled weight loss at twelve months compared with standard care, and most of the funding came from the company being tested.

What it actually is

A paid behaviour change program rather than a diet. In the studies, the working parts were a simple way to count food energy, weekly weigh-ins, group meetings and, in some versions, food provided. The trial evidence is narrower than the category suggests. It is mostly studies of one group program, now called WW and formerly Weight Watchers, and of the prepared-meal model used by Jenny Craig, Nutrisystem and the medically supervised very low calorie programs. Several widely used commercial products, including app-first programs, have little or no trial evidence at all.

How its fans say it works

Not a claim about carbs, fat or protein. The idea is about behaviour: structure, accountability, a simple way to count, group support and a set food plan help people stick with it, and sticking with it is what causes weight loss. Stated fairly, this is the only popular diet claim on this site that does not say it burns fat better than any other diet. It also happens to be the claim the studies back best. The head-to-head evidence agrees with it in an awkward way. In a review that pooled 48 trials and 7,286 people, the differences between named diets were tiny, while behaviour support added 3.23 kg of weight loss at six months.

What happened when calories were controlled

Best kind of study available: told what to eat, reported it themselves

People were told what to eat and then said what they ate. People usually say they ate less than they did, so what each group really ate is unknown.

Never, and here that is the right design, not a weakness. The program is about changing behaviour, so what matters is what people actually eat when nobody is watching. Controlling their food would remove the very thing being tested.

WRAP (Ahern 2017) tested how much of the program people need. 1,267 adults from 23 English family doctor practices were split two to five to five between brief advice with self-help materials, twelve weeks of the program, or 52 weeks of it. Weight lost at one year was 3.26, 4.75 and 6.76 kg. The program beat brief advice by 2.71 kg, and 52 weeks beat twelve by 2.14 kg, both clear results, and the differences were still clear at two years. 65 percent were followed up at one year and 68 percent at two. Over two years, the extra cost was 91 pounds per kg lost for the twelve-week program and 159 pounds per kg for the 52-week one. It was partly paid for by Weight Watchers International, through a UK Medical Research Council industry partnership award.
Jebb 2011 took 772 overweight and obese adults from family doctor practices in Australia, Germany and the UK. They got twelve months of standard care, as set out in national guidelines, or twelve months of free commercial program membership. At twelve months, counting dropouts at their last known weight, weight lost was 5.06 kg against 2.25 kg, a difference of 2.77 kg after adjustment, with a likely range of 2.03 to 3.50 kg. Counting dropouts as losing nothing, it was 4.06 against 1.77 kg. Among people who finished, it was 6.65 against 3.26 kg. 61 and 54 percent finished. It was paid for by Weight Watchers International, through a grant to the UK Medical Research Council.
Two studies ran the program in people with blood sugar problems. In 225 adults with prediabetes, twelve months on the commercial program led to 5.5 percent weight loss, against 0.2 percent on a national diabetes education program, with bigger gains in long-term blood sugar (HbA1c) and HDL. In 563 adults with type 2 diabetes across 16 US centres, long-term blood sugar fell 0.32 points against a 0.16 rise. 24 against 14 percent got it below 7.0, a clear result. Weight fell 4.0 against 1.9 percent, and 26 against 12 percent cut back their diabetes medicines, also a clear result.
Rock 2010 tested the prepared-meal model, with counselling and rewards for taking part, in 442 overweight and obese women over two years. Weight loss at 24 months was 7.4 kg (7.9 percent) for the group that went to a centre, 6.2 kg (6.8 percent) for the phone group, and 2.0 kg (2.1 percent) for usual care, a clear result. Weight data at 24 months was available for 92.1 percent of the women. That is unusually good follow-up for this research, and it makes the result more trustworthy than most.
Heshka 2003 ran a two-year version against self-help at six US university centres, in 423 adults. Counting everyone who started, weight loss was 4.3 against 1.3 kg at one year and 2.9 against 0.2 kg at two years, both clear results, and 71 and 75 percent finished. The part that gets dropped from summaries is in the same paper: by year two, the differences between groups in blood pressure, cholesterol, blood sugar and insulin were mostly not real.
Truby 2006 compared four commercial programs with each other over six months, in a UK community group recruited through a TV series. All four led to clear loss of weight and body fat against the comparison group, and the four did not really differ from each other. Average weight loss, counting everyone who started, was 5.9 kg, and fat loss 4.4 kg. The low carb program lost clearly faster in the first four weeks and was no better by the end.

What happened when people just ate it

The pooled reviews give the real-world picture, and their value is that they report dropouts alongside results. Gudzune 2015, which declares no funding source, pooled 45 studies, including 39 trials. At twelve months, people on the largest group program lost at least 2.6 percent more weight than the comparison or education groups. The prepared-meal program lost at least 4.9 percent more. A second prepared-meal program lost at least 3.8 percent more at three months. The very low calorie medical programs lost at least 4.0 percent more in the short term than counselling, with the edge fading after six months where that was reported. A low carb commercial program lost 0.1 to 2.9 percent more, and one meal replacement brand had mixed results. The review's own weak spots are the useful part. Many studies were short, many people dropped out, people knew which group they were in, and there was little evidence on how well people stuck with any program or what harms it caused. The earlier review, Tsai 2005, is blunter still. It found that apart from one study, the evidence for the major commercial and self-help programs was poor. The medically supervised very low calorie programs led to 15 to 25 percent weight loss in people who finished, but came with high costs, many dropouts, and a high chance of regaining 50 percent or more of the weight within one to two years. Because many studies did not account for all the dropouts, the reported results are probably a best case. Both reviews point the same way as the wider research. In a study comparing four popular diets directly, weight loss was linked to how well people said they stuck with the diet (a correlation of 0.60), and barely to which diet it was (0.07).

Protein, and whether it muddies the result

None of these programs sets a protein target, and none of the studies reported protein intake or measured muscle, so no lean mass figure can be given for any of them. That is a real gap, not a technicality. These are among the few weight loss programs people stay on for a year or more, and many people now combine a commercial program with a GLP-1 drug. The protein section of this site has the intakes that were measured and what each did, and anyone on one of these programs will have to add that layer themselves.

The measured intakes behind the protein figures are on the protein page.

What reliably moves

Measure	Direction	From
Body weight at twelve months	Down, by roughly 2.6 to 4.9 percent more than the comparison group	Across 45 studies, including 39 trials, the group program lost at least 2.6 percent more and the prepared-meal program at least 4.9 percent more, both against comparison or education groups.
Body weight at two years	Still better than the comparison, and shrinking	2.9 against 0.2 kg lost in the two-year self-help comparison, 7.4 kg against 2.0 kg in the prepared-meal study, and still clearly better at two years in WRAP. Nothing in this research runs longer.
Long-term blood sugar (HbA1c) in type 2 diabetes	Down	Down 0.32 points against a 0.16 rise over twelve months in 563 adults, with 24 against 14 percent getting it below 7.0, a clear result.
Diabetes medicine use	Down	26 against 12 percent of people cut back their diabetes medicines over twelve months, a clear result. This is the same kind of result the low carb diabetes studies found, and the kind a study's main measure often misses.
Blood pressure, cholesterol, blood sugar and insulin at two years	Mostly no difference against the comparison group	From the two-year self-help comparison, where the weight difference lasted and the blood test differences were mostly not real by year two. Reported here because it is usually left out.
Dropping out	High, in every study	39 and 46 percent did not finish the twelve-month check in the family doctor study, and 35 and 32 percent were not checked at one and two years in WRAP. The exception is the prepared-meal study, which kept 92.1 percent to 24 months.
Cost per kilogram lost	Measured, which is unusual	Over two years, 91 pounds per kg for a twelve-week referral and 159 pounds per kg for a 52-week one. Projected over 25 years, the twelve-week program beat brief advice on both cost and health, and the 52-week one came out at 2,394 pounds per year of good-quality life gained.

Long term, and serious health events

Two years is the limit, and the picture there is steady: the weight edge lasts but shrinks, and most of the gains in blood tests do not last. No study of a commercial program has counted heart attacks, strokes, broken bones or deaths. The funding has to be described both ways, because it is unusual. The two largest European studies were paid for by the company being tested, in both cases routed through the UK Medical Research Council, and both published findings that complicate the company's story: many dropouts in one, and a plain cost per kilogram in the other. The independent review, which declares no funding, reached a favourable view of the same program while naming short studies, many dropouts and people knowing their group as weak spots. The earlier independent review reached a much less favourable view and called the published results probably a best case. If you want one sentence, take this one. The effect is real. It is 2 to 5 percent of body weight more than doing nothing at a year. It is measured mostly in people who stayed in the study. And it is the largest effect any do-it-yourself diet on this site has shown against a real comparison.

Sources

Study in people2011
Primary care referral to a commercial provider for weight loss treatment versus standard care: a randomised controlled trial
The Lancet
772 adults in Australia, Germany and the UK were sent either to standard care from their doctor or to a free commercial weight loss program for a year. The program group lost 5.06 kg against 2.25 kg, about 2.77 kg more. 61 and 54 percent finished. Weight Watchers paid for the study through a grant to a UK research council.
772 adults in Australia, Germany and the UK randomised to twelve months of guideline standard care or free commercial programme membership. Minus 5.06 against minus 2.25 kg by last observation carried forward, adjusted difference minus 2.77 kg. Completion 61 and 54 percent. Funded by Weight Watchers International through a grant to the UK Medical Research Council.
Study in people2017
Extended and standard duration weight-loss programme referrals for adults in primary care (WRAP): a randomised controlled trial
The Lancet
1,267 adults got brief advice, twelve weeks of a weight loss program, or 52 weeks of it. After a year they had lost 3.26, 4.75 and 6.76 kg. The program beat brief advice by 2.71 kg, and the full year beat twelve weeks by 2.14 kg. Both gaps still held at two years. Weight Watchers helped pay for it.
1,267 adults randomised 2:5:5 to brief advice, twelve weeks or 52 weeks of the programme. One-year weight change minus 3.26, minus 4.75 and minus 6.76 kg. Programme beat brief advice by minus 2.71 kg and 52 weeks beat twelve by minus 2.14 kg, both p < 0.0001, still significant at two years. Co-funded by Weight Watchers International.
Study in people2003
Weight loss with self-help compared with a structured commercial program: a randomized trial
JAMA
423 adults at six US universities either helped themselves or joined a structured commercial program for two years. The program group lost 4.3 kg against 1.3 kg at one year, and 2.9 kg against 0.2 kg at two years. By year two, blood pressure, blood fats, blood sugar and insulin were mostly no different between the groups.
423 adults across six US academic centres, two years. Intention to treat weight loss minus 4.3 against minus 1.3 kg at one year and minus 2.9 against minus 0.2 kg at two years, both p < 0.001. Between-group differences in blood pressure, lipids, glucose and insulin were mainly non-significant by year two.
Study in people2010
Effect of a free prepared meal and incentivized weight loss program on weight loss and weight loss maintenance in obese and overweight women: a randomized controlled trial
JAMA
442 women were followed for two years. With free prepared meals, they lost 7.4 kg if they went to a center and 6.2 kg if coached by phone. Usual care lost 2.0 kg. Weight was measured for 92.1 percent of them at two years, the best follow up in this field.
442 women, two years. Weight loss at 24 months 7.4 kg (7.9 percent) centre-based, 6.2 kg (6.8 percent) telephone-based and 2.0 kg (2.1 percent) usual care, p < 0.001. Weight data available for 92.1 percent at 24 months, the best retention in this literature.
Study in people2006
Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC diet trials
BMJ
People from the community in the UK tried one of four commercial programs for six months, or no program. All four led to real weight and fat loss compared with no program, and they did about the same as each other. On average people lost 5.9 kg of weight and 4.4 kg of fat. The low carb program was faster for four weeks but no better by the end.
Four commercial programmes over six months in a community sample. All produced significant weight and body fat loss against control and the four did not differ significantly from each other. Intention to treat average 5.9 kg weight and 4.4 kg fat. The low carbohydrate arm lost faster for four weeks and was no better by the end.
Study in people2016
Comparison of Commercial and Self-Initiated Weight Loss Programs in People With Prediabetes: A Randomized Control Trial
American Journal of Public Health
225 adults with prediabetes joined either a commercial weight program or a national diabetes education program. The commercial group lost 5.5 percent of body weight at both six and twelve months, against 0.8 and 0.2 percent. Their long term blood sugar and good cholesterol also improved more.
225 adults with prediabetes randomised to a commercial weight management programme or a national diabetes education counselling programme. Weight loss 5.5 against 0.8 percent at six months and 5.5 against 0.2 percent at twelve, both p < 0.001, with greater improvements in HbA1c and HDL cholesterol.
Study in people2016
Randomized controlled trial of a nationally available weight control program tailored for adults with type 2 diabetes
Obesity
563 adults with type 2 diabetes at 16 US centers spent a year on a commercial program plus contact with a diabetes educator, or on standard care. Long term blood sugar fell 0.32 points on the program and rose 0.16 on standard care. Weight fell 4.0 against 1.9 percent. 26 percent against 12 percent cut back their diabetes drugs.
563 adults with type 2 diabetes across 16 US centres, twelve months, commercial programme plus diabetes educator contact against standard care. HbA1c minus 0.32 against plus 0.16 percentage points, 24 against 14 percent below 7.0 (p = 0.004), weight minus 4.0 against minus 1.9 percent, and 26 against 12 percent reduced diabetes medications (p < 0.001). Follow-up 86 percent.
Review of studies2015
Efficacy of commercial weight-loss programs: an updated systematic review
Annals of Internal Medicine
A review of 45 studies, 39 of which assigned people to groups by chance. At twelve months, the group program led to at least 2.6 percent more weight loss than control or education. The prepared meal program led to at least 4.9 percent more. The authors say many trials were short, many people dropped out, and there is little data on sticking with it or on harms.
45 studies including 39 randomised trials, primary funding source declared as none. At twelve months the group programme achieved at least 2.6 percent and the prepared-meal programme at least 4.9 percent greater weight loss than control or education. Limitations named by the authors: many trials short, high attrition, no blinding, and limited evidence on adherence or harms.
Review of studies2005
Systematic review: an evaluation of major commercial weight loss programs in the United States
Annals of Internal Medicine
An earlier, less upbeat review of US commercial programs. With one exception, it found the evidence weak. Medically supervised very low calorie programs got 15 to 25 percent weight loss in people who finished. But they cost a lot and many dropped out. People were likely to regain 50 percent or more within one to two years. The authors called the reported results probably a best case.
The earlier and less favourable review. Concluded that with one exception the evidence was suboptimal. Medically supervised very low calorie programmes produced 15 to 25 percent loss in completers with high costs, high attrition and a high probability of regaining 50 percent or more within one to two years. Reported results described as probably a best-case scenario.
Review of studies2014
Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis
JAMA
A review pooled 48 studies of 7,286 people on named diets. The differences in weight loss between one diet and another were tiny. Coaching on habits added 3.23 kg at six months, and exercise added 2.13 kg between six and twelve months. The advice: pick any diet the person will stick to.
48 randomised trials, 7,286 people, network meta-analysis. Weight loss differences between individual named diets were minimal. Behavioural support contributed 3.23 kg at six months and exercise 2.13 kg between six and twelve months. Conclusion: recommend any diet the patient will adhere to.
Study in people2005
Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial
JAMA
160 adults tried four popular diets for one year, and 50 to 65 percent finished. Weight loss tracked how well people said they stuck to their diet, not which diet it was. Each diet cut the ratio of bad to good cholesterol by about 10 percent.
160 adults, four popular diets, one year, completion 50 to 65 percent. Weight loss correlated with self-reported adherence at r = 0.60 (p < 0.001) and with diet type at r = 0.07 (p = 0.40). Each diet cut the LDL to HDL ratio by about 10 percent.

What people report

These are things people say about their own eating. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

The accountability of the weekly weigh-in is the most common reason people say it works for them. It is also the most common reason people say they dread it.
The simple points or portion system is often described as what made tracking doable, compared with counting calories directly.
Group meetings are valued highly by some and avoided entirely by others. Online-only members often report worse results, which fits WRAP, though WRAP did not test this.
Weight coming back after cancelling, reported very widely. That matches the review's finding of a high chance of regaining half or more after the very low calorie programs.
No effect, reported by people who went but did not follow the plan. That is what the link with sticking to the diet (0.60), against the link with diet type (0.07), describes.
Resenting paying a subscription to be told to eat less, the most common reason given for stopping.
Reports that the points system pushes people toward low calorie processed products over whole foods, which no study measured.

Sources: r/WeightWatchers, r/loseit and long-running program forums, plus the dropout and follow-up data inside the studies, which is the more useful half: 61 and 54 percent finished the twelve-month check in the family doctor study, against 92.1 percent followed to 24 months in the prepared-meal study. Otherwise unchecked self-report.

Who this is wrong for

Anyone on insulin or a sulfonylurea (a diabetes pill) who joins without telling their prescriber. Cutting back diabetes medicine was a result of the diabetes study, for 26 against 12 percent of people, and it happened under medical supervision.
Anyone with a history of eating disorders. Group weigh-ins and a points score are a poor fit. The largest review of this research found too little evidence to judge harms for any program, which is missing data, not proof of safety.
Anyone reading the result for people who finished as what to expect. In the same family doctor study, people who finished lost 6.65 kg, while counting dropouts as losing nothing gave 4.06 kg.
Anyone starting a medically supervised very low calorie program without knowing the regain data. Those programs led to 15 to 25 percent weight loss in people who finished, with high costs, many dropouts, and a high chance of regaining 50 percent or more within one to two years.
Anyone expecting the specific brand to be what works. Four commercial programs compared head to head over six months did not really differ from each other. In a review that pooled 48 trials, the differences between named diets were tiny, while behaviour support added 3.23 kg at six months.
Anyone for whom the subscription cost is what limits them, and who would be choosing between it and food. The cost analysis was done for a health system, not a household.

Questions

Do commercial weight loss programmes actually work?: Against standard family doctor care, yes, and this is the strongest head-to-head evidence any consumer diet product on this site has. Referral to a commercial program led to 5.06 kg lost against 2.25 kg on standard care at twelve months, and a 52-week referral led to 6.76 kg lost against 3.26 kg on brief advice. An independent review of 45 studies put the twelve-month edge at at least 2.6 percent of body weight for the group program and at least 4.9 percent for the prepared-meal one.
Who paid for those trials?: Mostly the company being tested. The two largest European studies were paid for by Weight Watchers International, in both cases through the UK Medical Research Council. That is disclosed in the papers, and it belongs in any honest reading of them. It also cuts both ways. The industry-funded studies published their high dropout rates and a cost per kilogram, and the review that declares no funding reached a favourable view of the same program.
Does the weight stay off?: Partly, for as long as anyone has looked, which is two years. The two-year comparison against self-help finished at 2.9 against 0.2 kg lost, down from 4.3 at one year. The prepared-meal study finished 7.4 kg down at 24 months. The very low calorie medical programs are the exception both ways: 15 to 25 percent loss in people who finished, and a high chance of regaining half or more within one to two years.
Is one programme better than another?: Not in the direct comparison. Four commercial programs run head to head for six months all beat the comparison group and did not really differ from each other, averaging 5.9 kg lost. In a review that pooled 48 trials, the differences between named diets were tiny, while behaviour support added 3.23 kg at six months. The structure seems to be what works, not the brand.
What about diabetes?: Two studies tested it. In prediabetes, twelve months led to 5.5 percent weight loss, against 0.2 percent on a national education program, with better long-term blood sugar and HDL. In type 2 diabetes, long-term blood sugar fell 0.32 points against a 0.16 rise, 24 against 14 percent got it below 7.0, and 26 against 12 percent cut back their diabetes medicines. That last figure is why anyone on insulin or a sulfonylurea should tell their prescriber before joining.