The method of serving and portion size affect the amount of food consumed at a single meal and contribute to the increasing prevalence of obesity in the United States, according to research published in the American Journal of Clinical Nutrition.

Researchers at the University of Pennsylvania conducted a study on the effects of portion size on overall food intake and found that large food portions typically served in restaurants and self-service during family meals may significantly affect the risk of obesity.

A total of 51 men and women, ages 21 to 40, participated in the study. The participants were not trying to either gain or lose weight. They completed four questionnaires to determine whether they usually exercised self-restraint in the presence of large portions of food.

On each test day the participants were given a test lunch that included a macaroni and cheese entrée. Twenty-seven participants received the entrée on individual plates in varying portions from small to large, and the other 24 participants served themselves as many helpings as they wanted. Five members of each group were identified as "plate cleaners" who ate the entire portion of each serving.

Both men and women ate more in response to a larger portion size, with the women overall consuming an average of 30 percent less food than the men. Fewer than one half of the men and women reported noticing any difference in the portion sizes they were given at meals.

Researchers suggest that people have the expectation that the amount of food served to them by others is appropriate, and that strategies to limit portion sizes in restaurants or at home should be developed in order to help slow the increasing incidence of obesity.

Other sources: American Journal of Clinical Nutrition