The increase in combat sports practice and the creation of weight divisions for fairer competitions led to dehydration practice as a strategy of inclusion in inferior divisions. However, this technique can damage kidney and heart functions due to alterations in blood volume. This study evaluated the acute effects of weight loss through dehydration on the kidney function of Mixed Martial Arts and Muay Thai fighters. The sample was composed of 30 athletes of both Mixed Martial Arts (n = 15) and Muay Thai (n = 15) fighters. Both groups went through two protocols for collecting data about the athlete's profile, vital signs, and urinary and blood samples in three different moments: before weigh-in, official weigh-in day, and fight day. The athletes' profiles and the dehydration methods employed were found to be consistent with those reported in the literature. The participants lost weight 1 month before the fight and had alterations that developed into glycosuria, leukocyturia, and proteinuria noted on both official weigh-in and combat days. Proteinuria and high creatinine depuration suggest acute kidney damage with an increase in filtration rate due to dehydration. As shown, there is a necessity for proper athlete orientation regarding dehydration and possible damage to the body's physiological integrity and sport performance, and developing a guide on more appropriate weight control protocols that do not put athletes' health at risk should be established and publicized.
Keywords: Mixed Martial Arts; Muay Thai; acute kidney injury; combat sports; dehydration.
Copyright © 2026 Antônio André Jarsen Pereira et al. Translational Sports Medicine published by John Wiley & Sons Ltd.