Movement & fitness

Relative energy deficiency in sport: under-fuelling, REDs, clinical assessment, and competing interpretations

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Energy availability describes dietary energy remaining for bodily functions after exercise expenditure, usually expressed relative to fat-free mass. Relative energy deficiency in sport, or REDs, is a clinical framework for harmful health and performance changes associated with problematic low energy availability. It can concern male and female athletes. A single low-calorie day or a lean appearance does not establish the syndrome.[1]

Energy availability, energy balance, and eating disorders differ

Low energy availability focuses on fuel remaining after exercise, whereas energy balance compares total intake with total expenditure. The female athlete triad concerns energy availability, menstrual function and bone health; REDs proposes a wider health and performance framework. Under-fuelling can be unintentional through time, food-access or knowledge barriers, or involve deliberate restriction and disordered eating. Those pathways call for different support.[2]

Brief adaptable exposure is not the same as persistent harm

The 2023 IOC consensus distinguishes adaptable from problematic exposure and notes individual moderating factors. Magnitude, duration and nutritional context matter; carbohydrate availability may contribute separately. It is therefore misleading to treat every calculated energy-availability value as an established disease boundary. Real-world intake and exercise-expenditure estimates are imperfect, and physiological effects do not all appear on one timetable.[1]

Screening and diagnosis are different stages

The IOC CAT2 uses initial screening, severity and risk stratification, then physician-led diagnosis and a care plan. Its four traffic-light levels support decisions about sport participation in a clinical context. The developers explicitly state that no singular validated diagnostic test exists. A positive screening indicator prompts assessment rather than proving that all symptoms have one nutritional cause.[3]

Different functions may recover at different speeds

The REFUEL bone report examined increased intake over twelve months. Improved energy status and menstrual outcomes did not produce a clear corresponding improvement in bone mineral density. Menstrual recovery and bone recovery are therefore different endpoints; resumed periods alone do not show that every consequence is reversed. Longer follow-up and clinically relevant fracture outcomes remain separate questions.[6]

A published critique challenges the breadth of the syndrome model

A 2024 critique argues that evidence for the broad REDs model is limited and that symptoms can reflect sleep, mental health, infection, injury or other clinical conditions independently of under-fuelling. The disagreement concerns attribution and diagnostic precision. It does not show that adequate nutrition is unimportant or that the experimental menstrual and bone findings should be ignored. Both overdiagnosis and missed nutritional problems matter.[7]

Care should investigate causes and remove barriers

The 2026 ACSM explanation emphasizes individualized clinical assessment and qualified nutrition support, including changes in training, travel, growth and reproductive stage. Food affordability and practical access can be as relevant as nutrition knowledge. An editorial application is to discuss recurring injuries, performance decline or menstrual changes with a qualified team without framing health solely around achieving a particular body weight.[2]

Evidence & uncertainty

There is evidence that insufficient fuelling can impair particular functions, but debate continues over how broadly the REDs framework should group symptoms and how reliably it can be diagnosed. Clinical assessment, experimental mechanisms and a questionnaire score provide different kinds of evidence. The Atlas does not resolve these debates by assigning a diagnostic label.[7]

Selected-source overview · Independent review pending

Published questions

Can men experience low energy availability?

Selected-source overview · Independent review pending. Read the evidence context.

The framework includes men, and selected controlled male experiments examine effects.[5]

Evidence behind this answer

Low Energy Availability with and without a High-Protein Diet Suppresses Bone Formation and Increases Bone Resorption in Men
randomized pilot trial · 2021
Indexed original abstract or official-page passages inspected in search; full-page access not established · Original indexed result passages: five-day exposure and protein comparison