But diets are popular for lots of reasons that defy scientific explanation and regardless of the evidence basis, they work. People who eat all meat, for example, lose weight, and people who eat only animal products lose weight. In most cases, it is because people who go on any diet tend to live healthier in multiple ways but a new review of 12 studies determined that people on a vegan diet lose around two kilograms more in the short term than dieters on a normal plan.
The review by Ru-Yi Huang of E-Da Hospital in Taiwan and colleagues is small, it included twelve randomized controlled trials, involving 1,151 dieters who followed a specific eating regime for between nine and 74 weeks. They included the Atkins diet, and ones recommended by the American Diabetes Association or the US National Cholesterol Education Program.
Overall, individuals assigned to the vegetarian diet groups lost significantly more weight (around 2.02 kilograms) than dieters who ate meat and other animal products. Vegetarians who followed a vegan diet lost even more weight. Comparatively, they lost around 2.52 kilograms more than non-vegetarian dieters. Vegetarians who do consume dairy products and eggs lost around 1.48 kilograms more than those on a non-vegetarian diet. People following vegetarian diets that prescribe a lower than normal intake of calories (so-called energy restriction) also shed more kilograms than those without any such limitations being placed on their eating habits.
Huang speculates that the abundant intake of whole grains, fruits and vegetables might play a role in the favorable results seen in vegetarian diets because whole-grain products and vegetables generally have low glycemic index values and don't cause blood sugar levels to spike. Fruits are rich in fiber, antioxidants, minerals and protective chemicals that naturally occur in plants. Whole-grain products contain soluble fiber. Such so-called good fiber helps to delay the speed by which food leaves the stomach and ensures good digestion. It also allows enough nutrients to be absorbed while food moves through the intestines.
Citation: Huang, R-H. et al (2015). Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials. Journal of General Internal Medicine. DOI 10.1007/s11606-015-3390-7