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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.