The effect of protein supplementation on markers of bone metabolism following repeated whole-body resistance exercise in men and women: A randomised controlled trial

This study examined acute, dose-dependent effects of protein supplementation on markers of bone metabolism in young healthy adults following two repeated bouts of whole-body resistance exercise in a randomised controlled trial. Resistance-trained men (n = 24) and women (n = 24) aged 18 to 35 y performed two within-day whole-body resistance sessions in the morning (Ex 1) and afternoon (Ex 2), separated by 4 h. Exercises comprised 3 × 8 repetitions at 75% 1 rep max (2 min rest between sets) involving latissimus dorsi pull down, single-leg press, and chest press. Participants (8 men and 8 women per group) were randomly assigned to drink either 15 g, 30 g or 60 g whey protein immediately after each exercise session. Resting venous blood samples were drawn after an overnight fast at 0 h (before Ex 1), 4 h (before Ex 2), 8 h, and 24 h. Samples were analysed for CTX, P1NP, BALP, OC, RANKL, OPG, Sclerostin (SOST), PTH, adjusted-calcium. The dose-dependent effects of protein supplementation were analysed using Linear Mixed Effects Models. p values were adjusted using the Holm-Bonferroni method and significance was accepted at p < 0.05. A significant main effect of time was shown for CTX, P1NP, OC, sRANKL, OPG, and PTH. CTX decreased between 0 h and 4 h, and 0 h and 8 h (p < 0.001). P1NP decreased between 0 h and 24 h (p = 0.008). OC decreased between 0 h and 4 h, and 0 h and 8 h (p < 0.001). sRANKL decreased between 0 h and 4 h, 0 h and 8 h, and 0 h and 24 h (p < 0.001). OPG decreased between 0 h and 8 h (p = 0.008). PTH decreased between 0 h and 8 h (p=0.003). A group * interaction was shown for OC (p=0.015), and a group effect for SOST (15 g and 30 g) (p=0.037). Protein supplementation ingested immediately after two repeated same-day resistance exercise sessions did not increase markers of bone formation at any dose. A decrease in markers of bone resorption, molecular signalling makers of bone metabolism, and PTH are likely due to responses in circadian variation.