Severely restricting energy intake for 24 h does not affect markers of bone metabolism markers at rest or in response to re-feeding

Purpose Intermittent energy restriction commonly refers to ad-libitum energy intake punctuated with 24 h periods of severe energy restriction. This can improve markers of metabolic health but the effects on bone metabolism are unknown. This study assessed how 24 h severe energy restriction and subsequent refeeding affected markers of bone turnover. Methods In randomised order, 16 lean men and women completed two, 48 h trials over 3-days. On day 1, participants consumed a 24-h diet providing 100 % (EB: 9.27 (1.43) MJ) or 25 % (ER: 2.33 (0.34) MJ) of estimated energy requirements. On day 2, participants consumed a standardised breakfast (08:00), followed by an ad-libitum lunch (12:00) and dinner (19:30). Participants then fasted overnight, returning on day 3. Plasma concentrations of C-terminal telopeptide of type I collagen (CTX), procollagen type 1 N-terminal propeptide (P1NP) and parathyroid hormone (PTH) were assessed as indices of bone metabolism after an overnight fast on days 1-3, and for 4 h after breakfast on day 2. Results There were no differences between trials in fasting concentrations of CTX, P1NP or PTH on days 1-3 (P>0.512). During both trials, consuming breakfast reduced CTX between 1-4 h (P<0.001) and PTH between 1-2 h (P<0.05), but did not affect P1NP (P=0.773) Postprandial responses for CTX (P=0.157), P1NP (P=0.148) and PTH (P=0.575) were not different between trials. Ad-libitum energy intake on day 2 was greater on ER (12.62 (2.46) MJ) than EB (11.91 (2.49) MJ). Conclusions Twenty-four hours severe energy restriction does not affect markers of bone metabolism.