Food Restriction Impairs Exercise-Induced Bone Mass Acquisition and Causes Iron Metabolic Disturbance with Storage Depletion in Young Female Rats

Abstract

Low energy availability is a core feature of Relative Energy Deficiency in Sport that impairs skeletal and hematologic health. However, the contributions of short-term energy restriction and exercise as well as their potential interactive effects remain unclear. This study aimed to clarify the effects of short-term food restriction on exercise-induced bone mass acquisition and its simultaneous impact on iron metabolism in young female rats. Female Sprague–Dawley rats (5 wk old) underwent environmental acclimation and treadmill running exercise training for 1 wk each and randomly grouped into seven groups. The groups included a sedentary and ad libitum feeding group, along with groups fed 90%, 70%, or 50% of the average ad-lib intake under sedentary or running exercise conditions for 15 d. The results showed low tibial bone mineral density (BMD) and ferritin levels and high serum iron levels due to a significant main effect of food restriction. Hematocrit-adjusted erythrocyte counts were unchanged, indicating an iron metabolic disturbance characterized by depleted stores despite high circulating iron. Exercise significantly increased tibial BMD, but the 50% food restriction groups (sedentary and exercise) showed significantly lower values than the exercise 90% group. Serum iron levels showed significant differences even in the 70% food restriction group compared with the 90% group. Tibial BMD and serum iron levels were weakly negatively correlated. This study revealed that, in young female rats, short-term 50% food restriction resulted in decreased BMD while short-term 70% and 50% food restriction resulted in iron metabolic disturbances under both sedentary and exercise conditions.