Portion size effects on weight gain in a free living setting

Abstract

ObjectiveExamine the effect of weekday exposure over six months to different lunch sizes on energy intake and body weight in a free-living sample of working adults.Design and MethodsAdults (n=233) were randomly assigned to one of three lunch size groups (400 kcal; 800 kcal; 1600 kcal) or to a no-free lunch control group for six months. Weight and energy intake were measured at baseline, and months 1, 3, and 6.ResultsLunch energy was significantly higher in the 800 and 1600 kcal groups compared to the 400 kcal group (p < 0.0001). Total energy was significantly higher for the 1600 kcal group compared to the 400 and 800 kcal groups (p = 0.02). Body weight change at six months did not significantly differ at the 5% level by experimental group (1600 kcal group: +1.1 kg (sd=0.44); 800 kcal group: −0.1 kg (sd=0.42); 400 kcal group: −0.1 kg (sd=0.43); control group: 1.1 (sd=0.42); p=.07). Weight gain over time was significant in the 1600 kcal box lunch group (p < 0.05).ConclusionsWeekday exposure for six months to a 1600 kcal lunch caused significant increases in total energy intake and weight gain.