An updated review by of 11 popular commercial diets found that only Jenny Craig and Weight Watchers show evidence for effective long-term weight loss.
Researchers from The Johns Hopkins University School of Medicine in Baltimore, Maryland reviewed evidence in support of Weight Watchers, Jenny Craig, Nutrisystem, Health Management Resources, Medifast, OPTIFAST, Atkins, SlimFast, The Biggest Loser Club, eDiets and Lose It!
These programs emphasize dietary change or meal replacement and behavioral counseling or social support, but do not necessarily address physical activity.
The team selected 45 dietary trials, including 39 randomized controlled trials comparing the diets to a control group, completed between 2002 and 2014. Many were sponsored by the commercial programs themselves.
In six trials, by the one-year mark, people on Weight Watchers had lost almost three percent more of their initial body weight than did people in control groups. But they did not lose any more weight on average than people in comparison groups who had access to behavioral counseling consultations with providers, which would also encourage weight loss.
Three trials found that people on Jenny Craig had at least 4.9 percent greater weight loss maintained at the one-year point compared with people in a control group or those in a behavioral counseling group.
Three trials found that people using Nutritystem had at least 3.8 percent greater weight loss compared to control or counseling at the three-month point, but no trials continued a full year.
Similarly, programs which require very low calorie intake, like Health Management Resources, Medifast and OPTIFAST, did demonstrate more weight loss after three months than a control or counseling group, but effectiveness seemed to diminish beyond six months.
Trials of the Atkins diet found between 0.1 and 2.9 percent greater weight loss than counseling after one year, but potential harmful side effects and drop-out rates from the program were rarely reported.
SlimFast trial results were mixed, and there was little evidence for weight outcomes for other programs.
Weight Watchers and Jenny Craig may be among the most effective programs because they are highly structured and often include in-person social support, say experts.
But weight loss with these programs is modest and likely below patients' expectations, which may make it harder for patients to stick with, and pay for, the programs long-term.
The trials in the review were not designed to pit the diets against each other and determine why one works better than another, but the review should help doctors and patients discuss whether or not a commercial diet program is a good choice, and if so, which one to try.
In addition to evidence of effectiveness, people should consider varying costs and time commitments.
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