The review, compiling data from 87 previous studies, shows the weight-loss effect does not depend on exercise or calorie-counting, and it occurs at a rate of approximately 1 pound per week.
Study authors Susan E. Berkow, Ph.D., C.N.S., and Neal D. Barnard, M.D., of the Physicians Committee for Responsible Medicine (PCRM), say that rates of obesity in the general population are skyrocketing, while in vegetarians, obesity prevalence ranges from 0 percent to 6 percent.
The authors found that the body weight of both male and female vegetarians is, on average, 3 percent to 20 percent lower than that of meat-eaters.
The review says vegetarian and vegan diets have also been put to the test in clinical studies.
The best of these clinical studies isolated the effects of diet by keeping exercise constant.
But the researchers found that a low-fat vegan diet leads to weight loss of about 1 pound per week, even without additional exercise or limits on portion sizes, calories, or carbohydrates.
Dr. Berkow, the lead author, says the research revealed that people can enjoy unlimited portions of high-fiber foods such as fruits, vegetables, and whole grains to achieve or maintain a healthy body weight without feeling hungry.
Dr. Barnard says 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.
Apparently insulin sensitivity is increased by a vegan diet, allowing nutrients to more rapidly enter the cells of the body to be converted to heat rather than to fat.
A team of researchers led by Tim Key of Oxford University recently found that meat-eaters who switched to a plant-based diet gained less weight over a period of five years.
Papers reviewed by Drs. Berkow and Barnard include several published by Dr. Key and his colleagues, as well as a recent study of more than 55,000 Swedish women showing that meat-eaters are more likely to be overweight than vegetarians and vegans.
White teens who reported that their parents did not approve of them having sex at this age were less likely to have engaged in pre-coital sexual behavior.
Both black and white youth who reported their parents did not want them to have sex were less likely to have engaged in sexual intercourse by the time they were 16 years old than those who perceived less parent disapproval of teen sex.
Brown said the media, schools, parents and pediatricians need to provide more accurate and timely sexual information to teens, otherwise, the media will continue to serve as a kind of sexual super peer that doesn't have the best interests of young people in mind.
As she says, it took many studies over a number of years to establish that violence in the media increased children's violent behaviour and to begin initiatives to reduce harmful effects.
Therefore, the researchers say, it may be prudent not to wait decades to conclude that the media are also important sources of sexual norms for youth.
The study was published in the April issue of Pediatrics, the journal of the American Academy of Pediatrics.