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. PURPOSE: This study aimed to investigate the effects of energy restriction and exercise on bone mineral density (BMD) and hormones during lactation. METHODS: 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. RESULTS: 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 versus 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. CONCLUSIONS: These results suggest that moderate energy restriction combined with RT promotes weight loss with no adverse effects on BMD during lactation.

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