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 reduced 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 osteocalcin (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.