Abstract / Summary
Abstract Introduction Bone appears sensitive to low energy availability (LEA), with prolonged exposure linked to compromised bone health. Causality, however, along with underlying mechanisms, and the role of macronutrient availability remain unclear. Purpose To investigate the influence of short-term energy and protein manipulation on bone biomarker and inflammatory cytokine responses to acute exercise. Methods Nineteen healthy, active young adults (9 females, 10 males) completed three 5-day dietary conditions in a randomized crossover design: adequate energy availability (AEA; 45 kcal·kgFFM·day -1 ), LEA (15 kcal·kgFFM·day -1 ) and LEA with protein matched to AEA (LEA-P). On days 1 and 5, participants completed a standardized exercise protocol comprising 45 min of cycling at 65% of pre-defined peak power output followed by a Wingate test, with blood samples collected at prespecified time-points to assess fasted and post-exercise bone biomarker and inflammatory cytokine responses. Results Fasted P1NP was lower following both energy-restricted trials compared with AEA, and remained lower during post-exercise recovery following LEA-P. CTX-1 was higher in the post-exercise recovery period following LEA-P only. Multiple inflammatory cytokines (IL6, IL8, IL10, ILRa, and IL1β) increased at distinct time-points in both energy-restricted trials. Overall, evidence for condition effects relative to AEA was more consistent following LEA-P than LEA. Conclusion Short-term energy restriction suppressed biomarkers indicative of bone formation and augmented the inflammatory cytokine response to exercise, with some, but less consistent evidence for increased bone resorption. Preserving protein intake did not attenuate these effects. In contrast, this condition was associated with more consistent and pronounced perturbations, potentially reflecting reduced carbohydrate availability rather than protein per se .