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Calcium homeostasis and bone metabolic responses to high-protein diets during energy deficit in healthy young adults: a randomized control trial

Jay J. Cao, Stefan M. Pasiakos, Lee M. Margolis, Edward R. Sauter, Leah D. Whigham, James P. McClung, Andrew J. Young, Gerald F. Combs Jr.
The American journal of Clinical Nutrition 2014 v.99 pp. 400-407
25-hydroxyergocalciferol, acid phosphatase, blood, bone density, bone formation, bone resorption, calcium, dietary energy sources, dietary protein, energy deficiencies, energy intake, excretion, high protein diet, homeostasis, insulin-like growth factor I, lean body mass, physical activity, randomized clinical trials, weight control, young adults
Although consuming dietary protein above current recommendations during energy deficit enhances blood lipid profiles and preserves lean body mass, concerns have been raised regarding effects of high-protein diets on bone health. To determine whether calcium homeostasis and bone turnover are affected by high protein and/or energy deficits, 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 days of weight maintenance (WM, days 1-10) preceded 21 days of energy deficit (ED, days 11-31), during which total daily energy deficit was 40% achieved by reduced dietary energy intake (~30%) and increased physical activity (~10%). Macronutrient composition (i.e., protein g·kg-1·d-1and % fat) was held constant from WM to ED. Ca absorption (ratio of 44Ca:42Ca) and circulating indices of bone turnover were determined at day 8 (WM) and day 29 (ED). Results showed that, 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). However, dietary protein had no effect on either urinary calcium excretion (P > 0.05) or the amount of calcium retained (P > 0.05). ED decreased serum IGF-1, increased serum tartrate-resistant acid phosphatase (TRAP) and 25(OH)Vit D concentrations (P < 0.01). Remaining markers of bone turnover, whole body bone mineral density and content were not affected by either protein level or ED (P > 0.05). These data demonstrate that short-term consumption high-protein diets do not disrupt Ca homeostasis or skeletal integrity. However, reductions in IGF-1 and elevated serum TRAP may indicate reduced bone formation and increased bone resorption in response to short-term ED.