Date of Award

Fall 11-11-2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Nutrition

First Advisor

Dan Benardot

Second Advisor

Anita Nucci

Third Advisor

Megan McCrory

Abstract

Title: Relationship of Energy Balance and Body Composition in Elite Female Gymnasts

Background: Studies suggest that athletes participating in weight-specific and appearance-based sports, including gymnasts, are at risk for developing negative energy balance both during and at the end of the day. A prolonged state of negative energy balance has been associated with lower fat-free mass, higher fat mass, and lower bone mineral density. Energy balance is defined as energy in minus energy out, and has been viewed in the past as a static, 24-hour system that begins anew each day. This study examined the relationship of energy balance and body composition (lean body mass, fat mass, body fat percent) and bone mineral density. Studies evaluating the relationship between energy balance and body composition have been conducted in the past, but few have taken into consideration hourly energy balance and the effects of multiple time periods of energy deficit of < -400kcal.

Purpose: The purpose of this study was to assess the relationship between energy balance and body composition in female gymnasts.

Methods: This study utilized a secondary analysis of existing data, and included 23 female elite, nationally ranked, gymnasts. Participants were included in this analysis if they had completed three-day food and activity records and had full body DEXA scans. The food and activity records were analyzed using NutriTiming®, which predicts RMR via the Harris-Benedict equation, uses a MET-based relative intensity activity scale, and accesses the USDA Nutrient Database for Standard Reference, Release 26. NutriTiming provides both 24-hour and hourly energy balance values. Original data were collected as part of a study conducted at Georgia State University in 1993 that had received IRB-approval. The current study also received IRB approval.

Results: Subject characteristics (mean ± SD) were: age (15.1 ±1. 58 years), height (151.3 ±7.7cm), and weight (45.63 ±8. 31kg). Average energy intake during the three days examined was 1375 kcal (±405), and the average predicted energy expenditure was 2430 kcal (± 298), for an energy balance of -1053 (± -438). Subjects were in a negative energy balance state the majority of the days analyzed. Spearman rho analysis found significant negative correlations between kcal consumed per kg bodyweight and body fat percent (r= -0.603, p=0.002), bone mineral density (r= -0.577, p=0.004), fat mass (r= -0.556, p=0.006), lean body mass (r= -0.466, p=0.025), lean body to height ratio (r= -0.466, p=0.025), and weight (r=-0.633, p=0.001). A significant amount of variance (R2= 0.435; SEE= ±0.05919, p=0.001) was explained in bone mineral density (dependent variable) with fat mass (independent variable).

Conclusion: The associations in this study are consistent with previous studies evaluating the relationships between energy balance deficits and body composition, indicating that poor energy balance is associated with lower lean and higher fat mass. Lean body mass, fat mass, and BMD were positively correlated with age, but 24-hour energy balance was negatively correlated with age (r= -0.484; p=0.019), suggesting that, although growing, subjects were consuming less energy with increasing age.

COinS