REDs: still under-recognised, especially in men.

REDs: challenges for male athletes

Relative Energy Deficiency in Sport (RED-S), or Relative Energy Deficiency Syndrome, describes disruption across multiple physiological systems, most commonly underpinned by chronic low energy availability (LEA).

Historically, REDs has been framed via the ‘Female Athlete Triad’. While it is now well established that REDs affects athletes of all genders, and awareness has improved in recent years, it remains under-recognised even in women. Notably, a recent study found 74% of female triathletes perceived menstrual disruption as “normal” during heavy training loads.

Recognition in men is almost certainly lower. This is partly due to the absence of an obvious early “red flag” equivalent to menstrual dysfunction. As a result, hormonal disruption may go un-investigated, allowing REDs to progress unnoticed until performance, health, or bone integrity is significantly compromised. Accessing appropriate support may also be more challenging for male athletes.

Key indicators of REDs in men

As with women, REDs in men often occurs without weight loss or a low BMI. In states of chronic LEA, the body compensates by down-regulating non-essential processes, which may present as:

• Reduced serum testosterone, sometimes within “low-normal” reference ranges (a severe primary indicator per IOC Cat 2 guidance)

• Reduced frequency of morning erections (<5 per week or a clear reduction from baseline)

• Reduced libido

• Impaired athletic performance, adaptation, or progression

• Persistent fatigue and delayed recovery

• Bone stress injuries

• Increased illness or recurrent/persistent injury

• Psychological effects, including low mood, irritability, and impaired concentration

• Gastrointestinal symptoms (e.g. bloating, nausea, altered bowel habits)

• Biochemical markers such as low ferritin (particularly if resistant to supplementation), low T3, and elevated cortisol

Long-term impacts

Failure to recognise and address RED-S in men has implications well beyond performance, affecting long-term health and wellbeing. Potential consequences include:

• Persistent suppression of testosterone

• Loss of bone mineral density and altered bone structure, increasing osteoporosis and stress fracture risk

• Adverse psychological and mental health outcomes

• Impaired immune function, with some associations to autoimmune conditions

• Reduced performance, recurrent injuries, and a “ceiling” on athletic potential

While many effects are reversible, prolonged LEA increases the risk of lasting adverse health impacts. This is particularly concerning given that REDs in men may remain unidentified for extended periods, with physiological consequences going under the radar.

Preventing and managing REDs

Low energy availability occurs when dietary intake fails to meet the combined demands of exercise expenditure and basic physiological function. Chronic LEA is widely accepted as a central driver of REDs, though it is not the sole factor. Low carbohydrate availability and within-day energy and carbohydrate deficits play a critical role, as do training and lifestyle stressors.

Common contributors include:

• Fasted training, particularly alongside high volume or intensity

• Long gaps between meals, especially around training

• Multiple daily sessions without adequate refuelling

• Restrictive dietary patterns framed as “healthy” (e.g. low-fat or rigid “clean eating”)

• Inadequate knowledge of fuelling requirements

High training loads, poor recovery, and broader life stress can further exacerbate REDs - and in some cases may be primary drivers even in the absence of overt LEA.

Managing REDs

Evidence consistently supports the following nutrition related outcomes in management of REDs:

1. Restoring energy availability relative to training demands

2. Ensuring adequate carbohydrate availability, particularly around key sessions

3. Aligning intake timing with training to avoid within-day deficits

Typically, these should be combined with management of training load and lifestyle stressors often as multi-disciplinary approaches to recovery.

Conclusion

REDs in men is prevalent and frequently missed. Early recognition, grounded in awareness, education and vigilance to subtle clinic signs, is essential to protect both performance and long-term health. Normalising conversations around energy availability and hormonal health in male athletes is a critical step toward prevention, timely intervention, and sustainable, health-focused athletic development.

Key References

Hackney, A.C. (2020) ‘Low energy availability, endocrine responses, and implications for male athletes’, Sports Medicine, 50(1), pp. 1–10.

Logue, D.M. et al. (2018) ‘Low energy availability in athletes: A review of prevalence, dietary patterns, physiological health, and sports performance’, Sports Medicine, 48(1), pp. 73–96.

Mountjoy, M. et al. (2018) ‘International Olympic Committee (IOC) consensus statement on Relative Energy Deficiency in Sport (RED-S): 2018 update’, British Journal of Sports Medicine, 52(11), pp. 687–697.

Mountjoy, M. et al. (2023) ‘RED-S Clinical Assessment Tool (CAT2): A clinical assessment and management tool for relative energy deficiency in sport’, British Journal of Sports Medicine, 57(17), pp. 1079–1088.

Tenforde, A.S. et al. (2016) ‘Parallels with the female athlete triad in male athletes’, Sports Medicine, 46(2), pp. 171–182.

Slater, J. et al. (2026) ‘An Exploratory Survey of Education Needs and Preferences Regarding Relative Energy Deficiency in Sport for Female Triathletes and Their Coaches’, Women in Sport and Physical Activity, 34(1).