The purpose of this study was to investigate the influence of an acute 24-hr fast versus usual 24-hr dietary intake on markers of bone turnover in collegiate lightweight male rowers. Bone turnover was measured by serum osteocalcin (OC) and urinary excretion of pyridinium cross-links (pyridinoline [PYD¿ and deoxypyridinoline ¿DPD]). Fasting subjects (F) (n = 14) reduced body weight by 1.7 +/- 0.5 kg but there was no significant change among nonfasting subjects (NF) (n = 13). Following 24 hr of fasting, PYD and DPD were lower in F (14.1 +/- 2.2 and 5.2 +/- 0.7 nmol/mmol creatinine, respectively) compared to NF (16.4 +/- 3.6 and 6.0 +/- 0.8 nmol/mmol creatinine)(p<.05). Fasting also reduce OC levels (4.8 +/- 0.4 ng/ml) compared to NF (6.1 +/- 0.9 ng/ml) (p<.01). Stepwise regression analysis of NF dietary intake indicated that energy intake explained a greater portion of the variation in bone turnover for PYD (34%), DPD (36%), and oseocalcin (46%) compared to other nutrients (p<.05). These results indicate that bone turnover is reduced by 24 hr of fasting and suggest a role for dietary energy intake in regulating bone turnover.