Effects of energy restriction and exercise on bone mineral density during lactation.

Abstract

Modest energy restriction combined with resistance training (RT) has been shown in nonlactating women to protect bone during periods of weight loss. However, there is a paucity of research on dietary interventions and exercise in lactating women aimed at promoting bone health and weight loss. This study aimed to investigate the effects of energy restriction and exercise on bone mineral density (BMD) and hormones during lactation. At 4 wk postpartum, participants were randomized to either a 16-wk intervention (diet restricted by 500 kcal and RT 3 d·wk) group (IG = 14) or minimal care group (CG = 13). Measurements included BMD by DXA, three 24-h dietary recalls, and hormones. Repeated-measures ANOVA was used to test for group differences over time. Energy intake decreased more in IG (613 ± 521 kcal) than CG (171 ± 435 kcal) (P = 0.03). IG lost more weight (5.8 ± 3.5 kg vs CG = 1.6 ± 5.4 kg, P = 0.02). BMD decreased over time, P < 0.01, with no group differences in lumbar spine (IG = 3.4% ± 2.5%, CG = 3.7% ± 3.3%) or hip (IG and CG = 3.1 ± 1.8%). Prolactin and estradiol decreased over time in both groups, P < 0.01. Basal growth hormone remained stable; however, there was a significant increase in growth hormone response to exercise in IG. These results suggest that moderate energy restriction combined with RT promotes weight loss with no adverse effects on BMD during lactation.