Low Energy Availability with and without a High-Protein Diet Suppresses Bone Formation and Increases Bone Resorption...

Suppression of insulin-like growth factor 1 (IGF-1) and leptin secondary to low energy availability (LEA) may contribute to adverse effects on bone health. Whether a high-protein diet attenuates these effects has not been tested. Seven men completed three five-day conditions operationally defined as LEA (15 kcal kg fat-free mass (FFM)^-1 day^-1) with low protein (LEA-LP; 0.8 g protein·kg body weight (BW)^-1), LEA with high protein (LEA-HP; 1.7 g protein·kg BW^-1) and control (CON; 40 kcal·kg FFM^-1·day^-1, 1.7 g protein·kg BW^-1). In all conditions, participants expended 15 kcal·kg FFM^-1·day^-1 during supervised cycling sessions. Serum samples were analyzed for markers of bone turnover, IGF-1 and leptin. The decrease in leptin during LEA-LP (-65.6 ± 4.3%) and LEA-HP (-54.3 ± 16.7%) was greater than during CON (-25.4 ± 11.4%; p = 0.02). Decreases in P1NP (p = 0.04) and increases in CTX-I (p = 0.04) were greater in LEA than in CON, suggesting that LEA shifted bone turnover in favour of bone resorption. No differences were found between LEA-LP and LEA-HP. Thus, five days of LEA disrupted bone turnover, but these changes were not attenuated by a high-protein diet.