The Role of Low Energy Availability in Predicting an Energy Deficiency and Menstrual Disturbances in Recreational and Competitive Atheltes

Open Access
- Author:
- Reed, Jennifer Lynn
- Graduate Program:
- Kinesiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 29, 2012
- Committee Members:
- Nancy Williams, Dissertation Advisor/Co-Advisor
Mary Jane De Souza, Committee Member
Terryl Johnson Hartman, Committee Member
Cynthia Bartok, Committee Member - Keywords:
- Energy availability
reproductive
exercise
females
athletes - Abstract:
- The Female Athlete Triad is a syndrome of three interrelated conditions: amenorrhea, osteoporosis, and low energy availability (EA). These conditions, either alone or in combination, pose significant health risks to exercising women. The overall goal of this dissertation was to help increase our understanding of EA, defined as the difference between dietary energy intake and exercise energy expenditure, normalized to kilograms of lean body mass, as a tool for assessing energy and menstrual status in a field setting. Short-term laboratory studies in sedentary women have identified a threshold of EA below which reproductive hormone secretion is disrupted, i.e., < 30 kcal/kg lean body mass but no studies have thoroughly examined the association of low EA and menstrual disturbances in trained women using more conventional methods to assess EA. We therefore assessed the prevalence of low EA (< 30 kcal/kg lean body mass) and its association with menstrual status and other indices of energy balance in exercising women outside controlled laboratory conditions. Study 1 was designed to assess the risk of low EA in Division I female soccer players during the pre, mid, and post season. We demonstrated that although the mean EA of the group was not low, a concerning percentage of these athletes exhibited low EA at some point during the season and that negative eating attitudes were also observed in athletes with low EA. Study 2 was designed to test whether EA discriminates disruptions in menstrual function in exercising premenopausal women. In contrast to our hypothesis, we demonstrated that EA did not discriminate menstrual status in a large sample of exercising women when using conventional methods to assess EA including self-reported diet logs, exercise logs, and heart rate monitors. The purpose of Study 3 was to determine if exercising women with menstrual disturbances who display reproductive recovery experience a greater increase in EA when compared to exercising women with menstrual disturbances who do not display reproductive recovery. We also tested the association between crossing a threshold value of 30 kcal/kg lean body mass and reproductive recovery. In contrast to our hypothesis, we demonstrated that trained women with menstrual disturbances who displayed reproductive recovery, whether defined as the resumption of menstrual bleeding or the resumption of menstrual bleeding preceded by ovulation, did not experience a greater increase in EA when compared to their counterparts who did not display reproductive recovery. Study 4 was designed to assess which of several indices of energy status best predicts the presence of an energy deficit and the presence of menstrual disturbances. We demonstrated that EA best predicts an energy deficiency, but that the ratio of measured to predicted resting energy expenditure best predicts a menstrual disturbance in exercising premenopausal women. Taken together, these data suggest that EA may not be a useful tool in assessing menstrual status in exercising women. Since an energy deficit is known to be related to disruptions in the menstrual cycle, the strong correlation between EA and energy deficiency we observed in Study 4, in the face of a non-significant association between EA and menstrual status found in Studies 2 and 3, is paradoxical. Possible explanations for the lack of association between EA and menstrual status include high variability in the measurement of the components of the EA index, dependence of menstrual status on aspects of energy balance not captured by EA, low statistical power, under or over reporting of dietary energy intake, and/or misclassification of menstrual status. Future studies are needed to more clearly understand the specific associations between the components of energy balance and menstrual status and to improve the accuracy of EA measurements.