The average person making the diet switch loses about 10 pounds according to a new meta-analysis of 15 studies…
However, the review found that people who were heavier to start with lost more weight. Greater weight loss is reported among men and among older participants.
Researchers with the nonprofit Physicians Committee reviewed 15 studies, conducted with 755 participants in Finland, Norway, Poland, Spain, Sweden, and the United States. The 15 studies varied in length, from as short as four weeks to as long as two years, with an average weight loss of 10 pounds over a 44-week period.
The research team searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials for articles through December 31, 2013. Additional articles were identified from reference lists. The participants were all adults, interventions included vegetarian diets of ≥4 weeks’ duration without energy intake limitations, and effects on body weight were reported. Two investigators independently extracted data using predetermined fields. Estimates of body weight change, comparing intervention groups to untreated control groups, were derived using a random effects model to estimate the weighted mean difference. To quantify effects on body weight of baseline weight, sex, age, study duration, study goals, type of diet, and study authorship, additional analyses examined within-group changes for all studies reporting variance data. We identified 15 trials (17 intervention groups), of which 4 included untreated controls. Prescription of vegetarian diets was associated with a mean weight change of −3.4 kg (95% CI −4.4 to −2.4; P<0.001) in an intention-to-treat analysis and −4.6 kg (95% CI −5.4 to −3.8; P<0.001) in a completer analysis (omitting missing post-intervention values). Greater weight loss was reported in studies with higher baseline weights, smaller proportions of female participants, older participants, or longer durations, and in studies in which weight loss was a goal. Using baseline data for missing values, I2 equaled 52.3 (P=0.10), indicating moderate heterogeneity. When missing data were omitted, I2 equaled 0 (P=0.65), indicating low heterogeneity. Studies are relatively few, with variable quality.
“The take-home message is that a plant-based diet can help you lose weight without counting calories and without ramping up your exercise routine,” says Neal Barnard, M.D., lead author of the study, president of the Physicians Committee, and an adjunct associate professor of medicine at the George Washington University School of Medicine and Health Sciences. “We hope health care providers will take note and prescribe this approach to patients looking to manage their weight and health.”
“If you’re overweight, losing just 5 to 10 percent of your body weight can slash the risk of both type 2 diabetes and cardiovascular disease,” says Susan Levin, M.S., R.D., C.S.S.D., a study author and director of nutrition education for the Physicians Committee. “As the weight comes off, you’ll start to see blood pressure, blood sugar, triglycerides, and cholesterol fall right along with it.”
Physicians Committee for Responsible Medicine, News Release. Neal Barnard. A Systematic Review and Meta-Analysis of Changes in Body Weight in Clinical Trials of Vegetarian Diets. Journal of the Academy of Nutrition and Dietetics, pub online Jan 21, 2015, DOI: http://dx.doi.org/10.1016/j.jand.2014.11.016