Objectives It has been reported that more than 30% of female endurance athletes suffer from sports disorders such as fatigue fractures and anemia. This is due to excessive physical activity and extreme dietary restrictions to improve athletic performance. Deficiency of energy and nutrients leads to low energy availability, which causes various health problems. In recent years, it has been reported that bone health and iron deficiency interact via the endocrine system, suggesting that fatigue fractures and anemia may develop in association with each other. The purpose of this study was to determine iron metabolism in young female rats with low bone mineral density (BMD) induced by a combination food restriction under running exercise. Methods Five-week-old Sprague-Dawley female rats were acclimatization period for 1 week and acclimated to treadmill running for 10 days. After that, the animals were divided into seven groups: the sedentary and ad libitum feeding (group F) and fed 90%, 70%, and 50% of the 3-day average of group F food intake in the sedentary (SED) or running exercise (EX) condition. Treadmill running exercise was performed at 25 m/min for 30 minutes. Fifteen days after the start of food restriction, blood and tibia were collected. The tibia was measured for BMD using the dual-energy x-ray absorptiometry method. The blood was measured for blood cell composition, serum iron, and ferritin. A two-way analysis of variance was used to examine the main effects and interactions of exercise and food restriction in six groups, excluding group F. We also evaluated the relationship between BMD of tibia and serum iron using Pearson's product fraction correlation coefficient. Results Food restriction had significant main effects on causing lower body weight, BMD of tibia, and ferritin. Moreover, food restriction had significant main effects on causing higher serum iron. On the other hands, there were no significant main effects of food restriction on red blood cell corrected for hematocrit. There was a significant negative correlation between BMD of tibia and serum iron. Conclusions Our study suggests that a food restriction increases serum iron in young female rats under running exercise condition and there is a correlation between low BMD and high serum iron. Funding Sources Funding from the scientific research of University of Tsukuba.

Female athletes follow a strict diet and perform rigorous exercise to boost their performance, which induces health issues called the female athlete triad (FAT), defined as the combination of disordered eating, amenorrhea, and low bone mineral density. It is known to have a significant effect on bones. However, its effects on the small intestine, which is responsible for nutrient uptake into the body, remain unclear. In this study, we created an animal model of FAT to examine its effects on digestive and absorptive molecules in the small intestine. Thirty 5-week-old female Sprague-Dawley (SD) rats with an initial body weight of about 147 g were divided into control (Con, n=7), exercise (Ex, n=7), food restriction (FR, n=8), and exercise plus food restriction (FAT, n=8) groups. The rats were subjected to four weeks of wheel running (Ex, FAT) and 50–40% food restriction (FR, FAT) to examine the effects on bone and typical digestive enzymes and transporters in the jejunum. Two-way ANOVA and the Kruskal–Wallis test were used for statistical analysis of normal and non-normal data, respectively. Four weeks of exercise and food restriction decreased bone weight (vs. other group p<0.01) and bone breaking power (vs. other group p<0.01). Villus height decreased in the jejunum (vs. other group p<0.01), but the expression of typical macronutrients digestive enzyme and absorptive molecules remained unchanged. In contrast, sucrase-isomaltase gene (vs. Ex p=0.02) and protein expression were increased (vs. other group p<0.05). The study findings show that FAT affects sucrase-isomaltase without histone methylation changes.