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 turno
ver in collegiate lightweight male rowers. Bone turnover was measured
by serum osteocalcin (OC) and urinary excretion of pyridinium cross-li
nks (pyridinoline [PYD] and deoxypyridinoline [DPD]). Fasting subjects
(F) (n = 14) reduced body weight by 1.7 +/- 0.5 kg but there was no s
ignificant change among nonfasting subjects (NF) (n = 13). Following 2
4 hr of fasting, PYD and DPD were lowerin F (14.1 +/- 2.2 and 5.2 +/-
0.7 nmol/mmol creatinine, respectively) compared to NF (16.4 +/- 3.6 a
nd 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 en
ergy intake explained a greater portion of the variation in bone turno
ver for PYD (34%), DPD (36%), and osteocalcin (46%) compared to other
nutrients (p <.05). These results indicate that bone turnover is reduc
ed by 24 hr of fasting and suggest a role for dietary energy intake in
regulating bone turnover.