Effects of Reduced Energy Availability on Bone Metabolism in Women and Men

Background: The short-term effects of low energy availability (EA) on bone metabolism in physically active women and men are currently unknown.

Purpose: We evaluated the effects of low EA on bone turnover markers (BTMs) in a cohort of women and a cohort of men, and compared effects between sexes.

Methods: These studies were performed using a randomised, counterbalanced, crossover design. Eleven eumenorrheic women and eleven men completed two 5-day protocols of controlled (CON; 45kcal·kgLBM·d) and restricted (RES; 15kcal·kgLBM·d) EAs. Participants ran daily on a treadmill at 70% of their peak aerobic capacity (VO peak) resulting in an exercise energy expenditure of 15kcal·kgLBM·d and consumed diets providing 60 and 30kcal·kgLBM·d. Blood was analysed for BTMs [β-carboxyl-terminal cross-linked telopeptide of type I collagen (β-CTX) and amino-terminal propeptide of type 1 procollagen (P1NP)], markers of calcium metabolism [parathyroid hormone (PTH), albumin-adjusted calcium (ACa), magnesium (Mg) and phosphate (PO)] and regulatory hormones [sclerostin, insulin-like growth factor 1 (IGF-1), triiodothyronine (T), insulin, leptin, glucagon-like-peptide-2 (GLP-2)].

Results: In women, β-CTX AUC was significantly higher (P=0.03) and P1NP AUC was significantly lower (P=0.01) in RES compared to CON. In men, neither β-CTX (P=0.46) nor P1NP (P=0.12) AUCs were significantly different between CON and RES. There were no significant differences between sexes for any BTM AUCs (all P values>0.05). Insulin and leptin AUCs were significantly lower following RES in women only (for both P=0.01). There were no differences in any AUCs of regulatory hormones or markers of calcium metabolism between men and women following RES (all P values>0.05).

Conclusions: When comparing within groups, five days of low EA (15kcal·kgLBM·d) decreased bone formation and increased bone resorption in women, but not in men, and no sex specific differences were detected.