Portion Power

It’s well known that ever-increasing portion sizes have paralleled an increase of obesity in the U.S. Nutritionist Barbara J. Rolls and her colleagues at Penn State have added another element to the literature on food and portion sizes (Am J Clin Nutr 2002; 76:1207).

For 4 weeks, 51 men and women were served lunch one day a week. At each meal, the subjects were presented with 1 to 4 portions of macaroni and cheese. One group received the meal on a plate, and could choose the portion they wanted, and a second group got it in a serving dish and could take as much as they wanted.

The subjects consumed 30% more when offered the largest portion than when offered the smallest one. The amount consumed was not affected by who determined the amount of food on the plate—nutritionists or subjects—or by the participants’ body mass index, gender, or scores of dietary restraint or disinhibition (Eating Inventory and Eating Attitudes Test). Five persons in each group were identified as “plate cleaners.” When this subgroup was excluded from the analysis, the effect on portion size remained—subjects in both groups consumed a significantly greater amount of food as portion size increased. In addition, the ratings of hunger and fullness after the meal did not vary, although intake increased with the amount of food that was presented, suggesting that portion size influences the development of hunger and satiety.

Learning about appropriate portions

The authors note that many people are often not aware of what constitutes an “appropriate portion” (J Am Diet Assoc 1998;98:458). Since this is a factor that can be easily modified, it should be addressed in the efforts to prevent obesity. One approach would be designing better educational materials about appropriate portions and how to read nutrition labels. Other suggested strategies are encouraging people to eat at restaurants that offer smaller portions, or to set aside part of the food at the beginning of meal, or to serve smaller amounts of food at home.