RMR and RMR ratio are not related to energy availability in elite and pre-elite athletes

Low energy availability (LEA), defined as an imbalance between dietary intake and exercise energy expenditure, has been associated with physiological and psychological dysfunction in athletes. The resting metabolic rate ratio (RMR_ratio), calculated as measured RMR divided by predicted RMR, is increasingly used as a surrogate marker for chronic energy deficiency when values fall below 0.9. Therefore, this study aimed to (1) compare the RMR_ratio across different predictive equations, (2) assess the association between energy availability (EA) and both RMR and RMR_ratio, and (3) explore the relationship between the RMR_ratio and phenotypical characteristics, including body composition, dietary intake, physical activity, sleep, and subjective well-being in Spanish competitive athletes. A total of 49 competitive athletes (33 males; 25.2 ± 5.6 years) from various sports were evaluated in this cross-sectional study. RMR was measured using indirect calorimetry and predicted using eleven validated equations. EA was estimated through dietary recalls and training logs. The prevalence of athletes classified as having metabolic suppression (RMR_ratio < 0.9) ranged from 34.7% to 93.9%, depending on the predictive equation used. No significant associations were observed between EA and either RMR or RMR_ratio. However, athletes with RMR_ratio ≥ 0.9 had significantly higher visceral adipose tissue mass, bone mineral content, and density. They also showed more favorable behavioral and psychological profiles, including greater sleep regularity, fewer sustained inactivity bouts, higher self-perceived performance, and lower general stress scores. In conclusion, while no relationship was observed between RMR or RMR_ratio and EA, the RMR_ratio was associated with different physiological, behavioral, and psychological parameters.