The more food young adults are served, the more they overeat.

Young and Nestle suggested that the increase in the portion size of food products evident in the United States during the past 20 years may be responsible for the epidemic of overweight and obesity. They based their conclusion on statistical correlations. The purpose of the present study was to provide experimental evidence to support their proposal. Cornell undergraduate students were given access to a buffet lunch on Monday, Wednesday, and Friday and were told this was a test of flavor enhancers. They were instructed to eat as much or as little as they wanted. On the same days of the following week, the subjects were divided into 3 groups. Each group was served either 100%, 125%, or 150% of the amount of food they had consumed the previous week. When larger amounts were served, significantly greater amounts of food were consumed. Each of the 4 foods that comprised the meal (soup, pasta, breadsticks, ice cream) increased significantly in proportion to the portion size. The data clearly support the hypothesis proposed by Young and Nestle and support the powerful role that environment plays in determining energy intake and potential increases in body weight.