Abstract
Despite some beneficial effects on bone, high protein diets have been conventionally considered a primary dietary risk factor for osteoporosis due to the acid load associated with protein catabolism. To test the hypothesis that high dietary protein diets do not negatively affect calcium homeostasis and bone turnover, 32 men and 7 women consumed diets providing protein at 0.8 (RDA), 1.6 (2X‐RDA), or 2.4 (3X‐RDA) g·kg‐1·d‐1 for 31 days in a randomized‐block design. Ten‐day of weight maintenance (WM, days 1–10) preceded 21‐day of energy deficit (ED, days 11–31), during which energy intake was restricted to 60% of WM. Ca absorption (ratio of 44Ca:42Ca) and circulating indices of bone turnover and were determined during WM (day 8) and ED (day 29). Regardless of energy state, urinary pH was lower (P < 0.05) for 2X‐RDA (6.28 ± 0.05) and 3X‐RDA (6.23 ± 0.06) compared to RDA (6.54 ± 0.06). ED induced weight loss (3.2 ± 1.0 kg body mass, P < 0.05), and a 13% reduction in serum IGF‐I (P < 0.01). Remaining markers of bone turnover, as well as urinary Ca excretion, absorption, bone mineral density and content were not affected by protein level and ED (P >; 0.05). These data demonstrate that consuming high protein diets do not disrupt Ca homeostasis and skeletal integrity, whereas reductions in IGF‐1 may suggest diminished bone formation during sustained ED.The study was supported by USDA ARS and USAMRMC.
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