Spring 2006• Volume XV, Number 2

Lightening the Load:
New Scientific Review Finds Vegetarian Diets Aid Weight Loss

There is good news for dieters looking for an easy way to slim down. A new scientific review of 87 studies on vegetarian diets and body weight concludes that excluding meat and other animal products from one’s diet can result in healthy 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., C.N.S., and PCRM president Neal Barnard, M.D., looked at randomized control trials and observational studies to find out the extent to which vegetarian diets help control weight. The authors also explored the mechanisms by which vegetarian and vegan diets lead to weight loss.

Observational Studies
Obesity is becoming a worldwide problem. The World Health Organization estimates that a total of 1.2 billion people are overweight or obese, and these numbers are rapidly increasing. Nearly half of the children in North and South America will be overweight by 2010, according to a recent report in the International Journal of Pediatric Obesity.

But better eating habits lead to slimmer bodies. Observational studies included in the review have shown that vegetarians have a body weight that is, on average, 3 percent to 20 percent lower than that of meat-eaters.

The body mass index (BMI) or body weight of vegetarians was observed to be lower than that of non-vegetarians in both genders, in blacks (both African-Americans and Nigerians), whites, and Asians. Similar observations have been reported in widely separated geographic areas.

The review found that obesity rates in vegetarian populations range from 0 percent to 6 percent. On average, vegans have a lower BMI than ovo-lacto vegetarians (who eat eggs and dairy), who, in turn, have a lower BMI than meat-eaters.

Clinical Trials
The review also examined randomized control trials that put the diet to the test. In a 12-week study that compared a 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 vegetarian 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.

Vegan diets seem to lead to weight loss even without a restriction on calorie intake.

Vegan diets seem to lead to weight loss even without a restriction on calorie intake. In clinical studies of low-fat vegan diets, mean body weight dropped significantly, even though energy intake and portion size was not limited.

Some research has combined a vegetarian diet with other lifestyle interventions. For example, 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.

How Does It Work?
How do vegetarian diets aid weight loss? One important mechanism may be a higher intake of vegetables, fruits, and other high-fiber foods, which are filling but low in calories.

A vegan diet also increases insulin sensitivity, which lets nutrients enter cells more quickly to be converted to heat instead of fat. Evidence suggests 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.

The simplicity of a vegan diet—which excludes meat, dairy products, and eggs—appeals to people busy with work and family, and many familiar recipes are easy to adapt. At least four studies published in peer-reviewed journals show that people give the low-fat vegetarian diet a high rating in terms of acceptability, and that the transition only takes about three weeks or less.

Of course, meatless meals can do more for health than just creating a slimmer body. Vegetarians also have lower rates of heart disease, diabetes, and high blood pressure, and are at a lower risk for some forms of cancer.

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