Weight cutting, hydration, kidney health and nutrition

Reviews of how fighters across combat sports lose weight before competition, what has been measured afterwards, and one society position stand on nutrition.

Research information, not medical advice. This page does not diagnose, screen or clear anyone to compete.

The sources on this page are three reviews, one before-and-after study and one position stand from a sports nutrition society, with one questionnaire study of kickboxers that screened for disordered eating. They cover combat sports as a group. None is limited to professional boxing.

This page describes research. It does not tell anyone how to cut weight.

What the sources report

  1. Weight-loss practices in combat sports athletes

    Zhong et al., 2024. Nutrients.

    Article type
    Systematic review
    Studied
    26 studies; 3,994 participants.
    Status
    Published in a peer-reviewed journal
    • 26 survey studies with 3,994 athletes from 14 combat sports were included. The review protocol was registered with PROSPERO.
    • Weight loss before competition was highly prevalent. Many athletes began as teenagers and usually lost less than 5% of body weight in the 7 to 14 days before competition.
    • More exercise and gradual dieting were the most common methods.

    Full recordDOI 10.3390/nu16071050

  2. Rapid weight loss and kidney function in combat sport athletes

    Lakicevic et al., 2021. Medicina.

    Article type
    Systematic literature review
    Studied
    Combat athletes in studies of rapid weight loss and kidney markers.
    Status
    Published in a peer-reviewed journal
    • The review covered studies of healthy athletes who lost about 5% of body weight within a week or less.
    • Most included studies reported higher creatinine, blood urea nitrogen and urine specific gravity after rapid weight loss.
    • The authors interpret these changes as dehydration and acute kidney damage.

    Full recordDOI 10.3390/medicina57060551

  3. Rapid weight-loss strategies and performance in combat sports

    Martínez-Aranda et al., 2023. International Journal of Environmental Research and Public Health.

    Article type
    Systematic review
    Studied
    16 studies; 184 combat-sport athletes.
    Status
    Published in a peer-reviewed journal
    • 16 studies with 184 athletes were included.
    • Six studies found no effect on performance from losing about 5% of body weight. Ten reported negative effects on performance, fatigue, mood or physiological measures.

    Full recordDOI 10.3390/ijerph20065158

  4. Rapid weight loss, resilience and pain sensitivity in kickboxers

    Çağlar et al., 2025. Frontiers in Psychology.

    Article type
    Before-and-after observational study
    Studied
    37 elite male kickboxers.
    Status
    Published in a peer-reviewed journal
    • 37 elite male kickboxers were measured before and after a one-month weight-loss period leading up to competition.
    • Pressure-pain thresholds in the thoracolumbar region were lower after the weight-loss period.
    • Four of six resilience subscale scores were higher after the period. Two did not change significantly.

    Full recordDOI 10.3389/fpsyg.2025.1545048

  5. ISSN position stand: nutrition and weight-cut strategies

    Ricci et al., 2025. Journal of the International Society of Sports Nutrition.

    Article type
    Society position statement informed by literature review
    Studied
    Combat-sport literature; no new participant cohort.
    Status
    Published in a peer-reviewed journal
    • The society sets out 16 position points developed from a literature review and approved by its research committee.
    • The points cover weight categories and weigh-in timing, energy systems, body weight between fight camps, supplements, calorie reduction during fight camp and recovery after weigh-in.

    Full recordDOI 10.1080/15502783.2025.2467909

  6. Mental health symptoms in current and former elite kickboxers

    Bilgoe et al., 2025. Discover Mental Health.

    Article type
    Cross-sectional survey
    Studied
    45 current and 29 former elite kickboxers.
    Status
    Published in a peer-reviewed journal

    In this study, 63% of current elite kickboxers screened positive for disordered eating.

    • 45 current and 29 former elite kickboxers answered screening questionnaires from the International Olympic Committee Sport Mental Health Assessment Tool 1.
    • Among current kickboxers, the most common positive screens were disordered eating (63%) and psychological distress (57%). Among former kickboxers, they were alcohol misuse (43%) and psychological distress (36%).

    Full recordDOI 10.1007/s44192-025-00328-w

Limits of this evidence

  • The reviews pool small studies that differ in sport, method and amount of weight lost.
  • The kidney review reports changes in blood and urine markers after rapid weight loss. Its abstract does not report long-term kidney outcomes.
  • A position stand is a society’s stated position, developed from a literature review. It is not a prescription for an individual fighter.

Fight Medicine Research Institute checked each source’s details against PubMed, Crossref, Europe PMC or the publisher. It has not carried out a formal critical appraisal of each paper.