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

• Published in: The American journal of clinical nutrition 2014-02, Vol.99 (2), p.400-407
• Main Authors: Cao, Jay J, Pasiakos, Stefan M, Margolis, Lee M, Sauter, Edward R, Whigham, Leah D, McClung, James P, Young, Andrew J, Combs, Gerald F
• Format: Article
• Language: English
• Subjects: 25-Hydroxyvitamin D; Absorption; acid phosphatase; Bioenergetics; blood serum; Body Composition - drug effects; Body Height; Body Mass Index; Body Weight; Bone and Bones - drug effects; Bone and Bones - metabolism; bone density; Bone Density - drug effects; bone metabolism; Calcium; Calcium, Dietary - administration & dosage; Calcium, Dietary - pharmacokinetics; Calcium, Dietary - urine; clinical nutrition; Clinical trials; Diet; dietary protein; Dietary Proteins - administration & dosage; energy intake; Energy Intake - drug effects; excretion; Female; Healthy Volunteers; high protein diet; Homeostasis; Homeostasis - physiology; Humans; insulin-like growth factor I; Insulin-Like Growth Factor I - metabolism; lean body mass; Male; men; Metabolism; Motor Activity; physical activity; Proteins; randomized clinical trials; Recommended Dietary Allowances; Tartrates - blood; Vitamin D - analogs & derivatives; Vitamin D - blood; volunteers; weight control; women; Young Adult; young adults
• ISSN: 0002-9165; 1938-3207
• DOI: 10.3945/ajcn.113.073809

Background: Although consuming dietary protein above current recommendations during energy deficit (ED) preserves lean body mass, concerns have been raised regarding the effects of high-protein diets on bone health.Objective: The objective was to determine whether calcium homeostasis and bone turnover are affected by high-protein diets during weight maintenance (WM) and ED.Design: In a randomized, parallel-design, controlled trial of 32 men and 7 women, volunteers were assigned diets providing protein at 0.8 [Recommended Dietary Allowance (RDA)], 1.6 (2 × RDA), or 2.4 (3 × RDA) g · kg−1 · d−1 for 31 d. Ten days of WM preceded 21 d of ED, during which total daily ED was 40%, achieved by reduced dietary energy intake (∼30%) and increased physical activity (∼10%). The macronutrient composition (protein g · kg−1 · d−1 and % fat) was held constant from WM to ED. Calcium absorption (ratio of 44Ca to 42Ca) and circulating indexes of bone turnover were determined at day 8 (WM) and day 29 (ED).Results: Regardless of energy state, mean (±SEM) urinary pH was lower (P < 0.05) at 2 × RDA (6.28 ± 0.05) and 3 × RDA (6.23 ± 0.06) than at the RDA (6.54 ± 0.06). However, protein had no effect on either urinary calcium excretion (P > 0.05) or the amount of calcium retained (P > 0.05). ED decreased serum insulin-like growth factor I concentrations and increased serum tartrate-resistant acid phosphatase and 25-hydroxyvitamin D concentrations (P < 0.01). Remaining markers of bone turnover and whole-body bone mineral density and content were not affected by either the protein level or ED (P > 0.05).Conclusion: These data demonstrate that short-term consumption of high-protein diets does not disrupt calcium homeostasis and is not detrimental to skeletal integrity. This trial was registered at www.clinicaltrials.gov as NCT01292395.