Randomized trial of the short-term effects of dieting compared with dieting plus aerobic exercise on lactation performance

Background: Limiting postpartum weight retention is important for preventin g adult obesity, but the effect of weight loss on lactation has nor been st udied adequately. Objective: We evaluated whether weight loss by dieting, with or without aer obic exercise, adversely affects lactation performance. Design: At 12 +/- 4 wk postpartum, exclusively breast-feeding women were ra ndomly assigned for 11 d to a diet group (35% energy deficit; n = 22), a di et plus exercise group (35% net energy deficit; n = 22), or a control group (n = 23). Milk volume, composition, and energy output; maternal weight, bo dy composition, and plasma prolactin concentration; and infant weight were measured before and after the intervention. Results: Weight loss averaged 1.9, 1.6, and 0.2 kg in the diet, diet + exer cise, and control groups, respectively (P < 0.0001) and was composed of 67% fat in the diet group and nearly 100% fat in the diet + exercise group. Ch ange in milk volume, composition, and energy output and infant weight did n ot differ significantly among,groups. However, there was a significant inte raction between group and baseline percentage body fat: in the diet group o nly, milk energy output increased in fatter women and decreased in leaner w omen. The plasma prolactin concentration was higher in the diet and diet exercise groups than in the control group. Conclusions: Short-term weight loss (approximate to 1 kg/wk) through a comb ination of dieting and aerobic exercise appears safe for breast-feeding mot hers and is preferable to weight loss achieved primarily by dieting because the latter reduces maternal lean body mass. Longer-term studies are needed to confirm these findings.