This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. While exercise provides undeniable health benefits, a high incidence of disordered eating, amenorrhea and osteoporosis occur among the increasing numbers of women participating in athletic training. Amenorrhea, the cessation of menstrual cycles for more than three consecutive months, has been postulated to affect up to 44% of women athletes. Hyposecretion of estradiol in this condition causes a loss of bone mineral density and an increased risk of fractures, osteoporosis and heart disease. Amenorrheic athletes also have a prolonged skeletal muscle phosphocreatinine recovery time, suggesting an impaired ability to perform repeated bouts of exercise and a competitive disadvantage compared to their regularly menstruating competitors. Previously, we showed that 4 days of low energy availability (EA=controlled energy intake minus controlled exercise energy expenditure), but not the stress of exercise, appeared to reduce both LH pulse frequency and the 24h mean and amplitude of the diurnal rhythm of leptin in young, healthy, women. Recent evidence in other mammals suggests that low carbohydrate availability, and not simply low energy availability, causes reproductive dysfunction and may regulate leptin levels. However, controlled experiments in humans are lacking. Understanding the short-term effects of carbohydrate availability on LH pulsatility and the diurnal leptin rhythm is critical in the development of nutritional guidelines for the protection of reproductive, skeletal and cardiovascular health in athletes and other physically active women. The proposed randomized repeated-measures experiment is designed to assess the independent effects of carbohydrate availability, defined as controlled dietary carbohydrate intake minus controlled exercise carbohydrate expenditure, and energy availability on the regulation of LH pulsatility, the diurnal leptin rhythm, and other metabolic hormones and substrates in young, healthy women
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