|Whigham Grendell, Leah|
Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2013
Publication Date: 2/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58820
Citation: Cao, J.J., Pasiakos, S.M., Margolis, L.M., Sauter, E.R., Whigham Grendell, L.D., Mcclung, J.P., Young, A.J., Combs, G.F. 2014. Calcium homeostasis and bone metabolic responses to high-protein diets during energy deficit in healthy young adults: a randomized control trial. American Journal of Clinical Nutrition. 99:400-407. Interpretive Summary: High-protein diets have been considered detrimental to bone health, although high-protein may help preserve lean body mass and improve blood lipid profile during weight reduction. This study investigated effects of consuming dietary protein above current recommended dietary allowance (RDA) during energy balance and energy deficit on calcium homeostasis and bone turnover in health young adults. Thirty-two men and 7 women participated in the study in a randomized-block design. Volunteers consumed diets providing protein at RDA, twice of RDA, or three times of RDA for 31 days. During days 1-10, energy intake of volunteers was adjusted to maintain the stable body weight. During days 11-31, energy intake was reduced by 30% and energy expenditure through physical activity was increased by 10% to achieve total 40% energy deficit. Ca absorption and circulating indices of bone turnover were determined at day 8 during weight maintenance and day 29 during energy deficit. Results showed that consuming high protein increased urinary acidity and had no effect on either urinary calcium excretion or the amount of calcium retained. Energy deficit decreased serum IGF-1, a bone anabolic factor, and increased serum tartrate-resistant acid phosphatase, a bone resorption marker. However, markers of bone turnover, whole body bone mineral density and content were not affected by protein level. Our data demonstrate that short-term consumption of high-protein diets does not disrupt Ca homeostasis or skeletal integrity and is not detrimental to bone health. However, short-term weight reduction may compromise bone health.
Technical Abstract: 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.