Doctoral Dissertation Research: Female reproductive ecology and energy availability in a high adiposity human population

Yale University, New Haven CT

Investigators

Abstract

Human reproduction requires females to invest significant amounts of caloric energy into pregnancy, lactation, and childcare. It has been proposed that females have evolved ways to vary how much energy they spend on reproduction in response to energy availability, which has commonly been indexed by body fat. Excess body fat can adversely affect reproductive hormone pathways and disrupt menstrual cycles, and it is not clear whether this might in part be due to the influence of body fat levels on sensitivity to stress. This research project examines female reproductive function among women in a population with comparatively high body fat levels who have been shown previously - in contrast to other populations - to experience relatively low rates of irregular menstrual cycles. In addition to contributing to a greater understanding of the diversity of body fat-reproductive function associations, this project supports scientific training for female graduate students and scientists in the research community, and helps strengthen scientific partnerships with local communities. Reproductive biologists have developed two scientific models to describe the relationship between ovarian function and caloric energy availability. The Lipostatic Model suggests that female reproductive function is closely associated with body fat levels, while the Metabolic Model suggests that female reproductive function is more strongly affected by caloric energy deficiencies. This project tests these models among females with high body fat levels by 1) examining the prevalence of menstrual irregularity and loss of ovulation among a study sample of approximately 150 females of mid-reproductive age, and 2) assessing reproductive hormone levels across the menstrual cycle in relation to body fat levels and physical activity. By using gold-standard dual x-ray absorptiometry to estimate subcutaneous fat together with wearable physical activity monitors to quantify daily physical activity, the project can address the question of whether high body fat levels protect female reproductive function from energetic stress caused by increased caloric demands. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.