Beyond BMI: Body Composition Misclassification and Relative Energy Deficiency in Sport as Overlooked Threats to Athletic Performance -A Narrative Review
DOI:
https://doi.org/10.12775/QS.2026.67.74351Keywords
body mass index, RED-S, low energy availability, athletic performance, body compositionAbstract
Background. Body mass index (BMI) remains the default screening tool for body composition in athletes, even though it was validated in sedentary populations and cannot distinguish muscle from fat.
Aim. To summarize current evidence on the limitations of BMI in athletic populations, focusing on both the misclassification of muscularity and the under-detection of Relative Energy Deficiency in Sport (RED-S), and their combined implications for athletic performance.
Material and methods. A narrative review was conducted using PubMed, Scopus and Google Scholar, covering studies published between 1997 and 2025 on BMI, body composition, RED-S and athletic performance.
Results. BMI misclassifies a substantial share of muscular athletes as overweight or obese despite normal body fat, while athletes with clinically significant low energy availability can present with unremarkable BMI. Nearly half of athletes across sports show low energy availability, which impairs endurance, coordination, judgment and explosive power. Whether RED-S constitutes a single coherent syndrome remains scientifically contested.
Conclusions. BMI alone is inadequate for assessing athlete health and performance risk in either direction; validated, multidimensional screening tools should replace it as the default standard.
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Copyright (c) 2026 Aleksandra Syguda, Kamila Tarnawska, Anna Strózik, Agnieszka Szcześniak, Weronika Matyja
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