title: Calcium homeostasis and bone metabolic responses to high-protein diets during energy deficit in healthy young adults: a randomized controlled trial.
abstract: 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.
  
  
  METHODS
  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 (44)Ca to (42)Ca) 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: USDA, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND (JJC, LDW, and GFC); the Military Nutrition Division, US Army Research Institute of Environmental Medicine, Natick, MA (SMP, LMM, JPM, and AJY); and the School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND (ERS).
authors.forename: Jay J
authors.initials: JJ
authors.lastname: Cao
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Pasiakos
authors.forename: Lee M
authors.initials: LM
authors.lastname: Margolis
authors.forename: Edward R
authors.initials: ER
authors.lastname: Sauter
authors.forename: Leah D
authors.initials: LD
authors.lastname: Whigham
authors.forename: James P
authors.initials: JP
authors.lastname: McClung
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Young
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Combs
mesh_terms: D000042:Absorption; D001823:Body Composition / Q000187:drug effects; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D015519:Bone Density / Q000187:drug effects; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000652:urine; D004044:Dietary Proteins / Q000008:administration & dosage*; D002149:Energy Intake / Q000187:drug effects*; D005260:Female; D064368:Healthy Volunteers; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D009043:Motor Activity; D064167:Recommended Dietary Allowances; D013644:Tartrates / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D055815:Young Adult
chemical_list: D002136:Calcium, Dietary; D004044:Dietary Proteins; D013644:Tartrates; D014807:Vitamin D; D007334:Insulin-Like Growth Factor I; C104450:25-hydroxyvitamin D; C029768:tartaric acid