Scientific Review Finds Vegetarian Diets Can Lead to Weight Loss
There is good news for dieters looking for an easy way to slim down. A scientific review of 87 studies on vegetarian diets and body weight concludes that excluding meat from one’s diet can result in weight loss, even without additional exercise or calorie-counting. The review, which appears in April’s Nutrition Reviews and is coauthored by Susan Berkow, Ph.D., and PCRM president Neal Barnard, M.D., looked at randomized control trials and observational studies to find out the extent to which vegetarian diets helped control weight.
Observational studies have shown that vegetarians have a body weight that is, on average, 3 percent to 20 percent lower than that of meat-eaters. While obesity rates in America continue to rise at an alarming rate, the prevalence of obesity in vegetarian populations ranges from 0 percent to 6 percent. In general, vegans have a lower body mass index (BMI) than ovo-lacto vegetarians (who eat eggs and dairy), who, in turn, have a lower BMI than meat-eaters.
The review also examined randomized control trials, which provide a more accurate look at diet and weight loss. Some studies have combined prescribing a vegetarian diet with other lifestyle interventions. In one study, Dean Ornish, M.D., compared adults with coronary artery disease on a low-fat vegetarian diet and a walking program with adults with the same disease receiving care from their physicians. After one year, those in the vegetarian diet group had lost an average of 23.7 pounds compared with a gain of 3.2 pounds in the physician’s care group.
Other studies have controlled for the effect of exercise. In a 12-week study that compared a trial group of individuals on a vegetarian diet deriving 10 percent of calories from fat with a control group of individuals following guidelines of the American Diabetes Association, the experimental group lost 15.9 pounds while the control group lost 8.4 pounds. Both groups in this study were asked not to alter their exercise habits. Another study with 64 postmenopausal women found that those on a low-fat vegan diet lost about one pound per week without additional exercise or limits on portions.
A low-fat vegetarian diet lets people enjoy unlimited portions of high-fiber foods such as vegetables, fruits, and whole grains. These foods, which are low in calories and high in fiber, help people feel full. A vegan diet also increases insulin sensitivity, which lets nutrients enter cells more quickly to be converted to heat instead of fat. “There is evidence that a vegan diet causes an increased calorie burn after meals, meaning plant-based foods are being used more efficiently as fuel for the body, as opposed to being stored as fat,” said Dr. Barnard.
Vegetarian diets can do more for health than just creating a slimmer body. Vegetarians have lower rates of heart disease, diabetes, and high blood pressure, and are at a lower risk for some forms of cancer.