Portion Size Effects on Body Weight: Free Living Setting

The study purpose was to evaluate the effects of portion sizes on body weight and energy intake in a free-living setting. 223 healthy adults were recruited from an urban worksite and randomized to one of four groups for a six-month period. The groups were: 1) 400 kcal box lunch; 2) 800 kcal box lunch; 3) 1600 kcal box lunch; or 4) no box lunch. Participants were required to pick up a box lunch every week day for six months. Control participants did not receive a box lunch and were instructed to eat their usual lunch. Participants were weighed and dietary intake measured at baseline, one, three and six months. It was hypothesized that at six months, participants in the 1600 kcal box lunch would gain more weight and have higher energy intake than those in the other groups.