Study Examines Effects of Popular Diets on Weight Loss and CV Risk Factors

Examining the efficacy of various weight loss programs, new evidence has found that Atkins, Weight Watchers, and Zone diets achieved modest and similar long-term weight loss, and data is conflicting and insufficient to identify one popular diet as being more beneficial than its counterparts, according to a study published Nov. 11 in Circulation: Cardiovascular Quality Outcomes.

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For years a number of unique diets have been advertised to the greater public promoting weight loss and improving cardiovascular risk factors. Four popular programs among North Americans include Atkins, South Beach, Zone and Weight Watchers. Each diet has its own philosophy and targeted approach. Atkins is a four-phase diet based on very low carbohydrate intake, with unlimited protein and fat consumption. South Beach meanwhile is a three-phase low-carbohydrate/high-protein diet, focusing on lean protein, mono- or polyunsaturated fats, and low-glycemic index carbohydrates. Zone follows a similar regimen, but recommends the consumption of low-fat proteins and small amounts of good fat (e.g. olive oil, avocado). Finally Weight Watchers is a full food, physical activity, and behavior modification plan that uses weekly group sessions and a personalized points system to provide caloric intake restrictions.

Led by principal author Renée Atallah, MSc, Centre for Clinical Epidemiology, Jewish General Hospital, McGill University, Montreal, QC, Canada, investigators searched MEDLINE, EMBASE, and the Cochrane Library of Clinical Trials to identify randomized controlled trials with follow-up greater or equal to four weeks that examined the effects of these four popular diets on weight loss and cardiovascular risk factors. Identifying 12 trials (n=2,559) with follow-up greater or equal to 12 months: 10 vs. usual care (five Atkins, four Weight Watchers, and one South Beach) and two head-to-head (one of Atkins, Weight Watchers and Zone, and one of Atkins, Zone and control). At 12 months, the 10 trials comparing popular diets to usual care demonstrated that only Weight Watchers was consistently more effective in reducing weight (range of mean changes: −3.5 to −6.0 kg vs. −0.8 to−5.4 kg; P<0.05 for 3/4 randomized controlled trials). However, the results of the two head-to-head randomized controlled trials suggest that Atkins (range: −2.1 to −4.7 kg), Weight Watchers (−3.0 kg), Zone (−1.6 to −3.2 kg), and control (−2.2 kg) all achieved modest long-term weight loss. Extended twenty-four-month data showed that weight lost with Atkins or Weight Watchers was partially regained over time.

According to the authors, “Despite their popularity, the Atkins, South Beach, Weight Watchers and Zone diets seem to only achieve modest sustained weight loss.” They add that moving forward, “comprehensive lifestyle interventions aimed at curbing both adult and childhood obesity are urgently needed. Interventions that include dietary, behavioral, and exercise components, as well as legislative measures and industry regulations, may be better suited to the multifaceted obesity epidemic.”

Keywords: Life Style, Behavior Therapy, Follow-Up Studies, Weight Loss, Canada, Glycemic Index, Risk Factors, Weight Reduction Programs, Plant Oils, Diet, Carbohydrate-Restricted, Persea, Motor Activity, Obesity, Energy Intake, MEDLINE

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