Use of Resting Metabolic Rate Ratio as a Relative Energy Deficiency in Sports Indicator in Female Athletes

Female athletes are at risk of relative energy deficiency in sport (REDs) if energy intake is insufficient relative to demand. REDs is commonly identified via low energy availability (EA), which is determined by measuring dietary intake, exercise energy expenditure, and lean body mass. Due to inconsistent methods to measure each component of EA, the use of resting metabolic rate (RMR) ratio is proposed as an alternate method to identify REDs.

The purpose of this study was to identify REDs prevalence among a sample of physically active college-aged females using RMR ratio and correlate this with EA.

Females (18-24 y) who were members of a NCAA division 1 athletics team or highly physically active (greater than 4 d/wk) participated in the study. Body composition was measured using air displacement plethysmography. RMR was measured using indirect calorimetry. Participants reported dietary intake via a 24-h recall for 1-3 d. EA was calculated using an averaged activity factor of 1.67 to determine exercise energy expenditure. RMR was calculated using standard equations (Harris-Benedict, Owen, and Cunningham).

A total of 77 physically active female college students participated, including 53 NCAA division 1 athletes. Mean EA was 24.5 ± 12.8 kcal/kg fat-free mass/d and 63% of participants met criteria for low EA (<30 kcal/kg fat-free mass/d). Mean RMR ratio was 1.08 ± 0.16, with 19% of the sample having low RMR ratio (below 0.9). Overall, 14% of participants had both low EA and low RMR ratio. There were no differences in EA or RMR ratio between the collegiate athlete and recreational athlete groups.

Physically active female college students, including collegiate athletes, exhibited suboptimal EA. Low RMR ratio appeared to be a more sensitive indicator of REDs risk than low EA.