What Is Low Energy Availability and How Does RED-S Develop?

Key Takeaways

• Low energy availability (LEA) occurs when the energy remaining after exercise is not enough to support normal body function. The clinical threshold is below 30 kcal per kilogram of fat-free mass per day.
• RED-S (Relative Energy Deficiency in Sport) develops when LEA persists over weeks or months, affecting bone health, hormonal function, immunity, and performance.
• LEA is not limited to elite athletes. Recreational runners, gym-goers, cyclists, and anyone combining regular training with insufficient food intake are at risk.
• RED-S affects both men and women. In men, it often presents as low testosterone, reduced libido, and unexplained performance decline.
• The primary fix is increasing energy intake through consistent, nutrient-dense meals, particularly around training sessions.

Are You Training Hard but Running on Empty?

You train consistently. You eat what feels like a reasonable amount. But you are always tired, your performance has stalled, and recovery takes longer than it should.

What you may be experiencing is low energy availability: a mismatch between how much fuel you take in and how much your body actually needs. It is more common than most people realise. It is not a willpower issue. It is a fuelling problem.

What Is Low Energy Availability?

Energy availability is the energy left for normal physiological function after subtracting the cost of exercise. The formula: dietary energy intake minus exercise energy expenditure, expressed relative to fat-free mass.

Below 30 kcal per kilogram of fat-free mass per day is the clinical threshold for low energy availability. Optimal sits at or above 45 kcal/kg FFM/day, according to the IOC consensus framework on RED-S.

LEA is not always deliberate. A demanding work schedule means meals get skipped. Appetite drops after a hard session, so post-workout eating gets delayed or missed. Training load increases without a matching increase in food. None of this requires a conscious decision to restrict. It just requires a busy life and insufficient awareness of how much fuel hard exercise demands.

What Is RED-S and How Does It Develop?

RED-S (Relative Energy Deficiency in Sport) is what happens when low energy availability is sustained over weeks or months. It is not a single symptom. It is a multi-system syndrome affecting performance, hormones, bones, immunity, and cardiovascular health.

When the body lacks enough energy to cover both exercise and normal function, it starts rationing. Hormonal regulation, bone metabolism, and immune function are deprioritised to keep vital organs running.

The International Olympic Committee formally recognised RED-S in 2014, expanding the earlier "female athlete triad" framework to include male athletes and a broader range of consequences. The updated IOC consensus statement remains the foundational clinical reference.

Who Is at Risk?

The assumption that RED-S only affects elite athletes is one of the most persistent misconceptions in sports nutrition. Recreational runners, gym-goers, dancers, cyclists, and triathletes are all at risk. Anyone combining regular exercise with insufficient fuelling can develop LEA.

Specific risk factors include sports with weight categories or aesthetic demands, athletes who restrict food to manage body composition, and those who train twice daily without adjusting intake. Post-exercise appetite suppression is also a significant driver. The body's hormonal response to intense exercise actively suppresses hunger, so the athletes who need to eat most urgently often feel least like eating. That is a physiological response, not a signal to skip the meal.

Male athletes are affected too. RED-S in men tends to present with low testosterone, reduced libido, impaired recovery, and performance decline. These symptoms are often attributed to overtraining rather than underfuelling.

What Are the Warning Signs?

RED-S affects multiple systems, which is why the symptom picture can look confusing.

Performance and recovery: Decreased strength and endurance. Longer recovery between sessions. Increased frequency of stress fractures.

Hormonal: Disrupted or absent menstrual cycle in women. Low testosterone and reduced libido in men.

Bone health: Stress fractures. Reduced bone mineral density.

Psychological: Irritability, low mood, difficulty concentrating. Disordered eating behaviours.

General: Persistent fatigue that sleep does not resolve. Frequent illness. Poor sleep quality. Gastrointestinal disturbance.

If you recognise three or more of these, act on it. Review your fuelling first. In moderate-to-severe cases, consult a sports dietitian. These symptoms do not resolve by training less alone. The body needs more energy in, not simply less energy out.

Research published in the British Journal of Sports Medicine  consistently identifies these as markers of compromised function in athletes with sustained LEA.

How Is Low Energy Availability Addressed?

The primary intervention is increasing energy intake: consistent, nutrient-dense fuelling across the day, with particular attention to eating around training. Reducing training load alone does not fix the underlying deficit.

Eat before and after every session, not just on hard days. Do not skip meals during high-training periods, even when appetite is low. Prioritise carbohydrates before and after training to replenish glycogen. Include protein, complex carbohydrates, and healthy fats at each meal. Treat post-exercise appetite suppression as a reason to plan ahead, not a reason to eat less.

Balanced nutrition is about more than protein. That matters especially in the context of LEA, where hormonal function, bone health, and immune response all depend on adequate micronutrient intake alongside macronutrients.

For athletes who struggle to eat enough around training, Whole Supp's Superfood Meal Shake provides 31g of protein and 13 superfoods in a single serving, with complex carbohydrates from oats for sustained energy and healthy fats that support hormone production.

In moderate-to-severe cases, working with a sports dietitian is strongly recommended. The English Institute of Sport provides guidance on RED-S awareness and athlete nutrition support.

Fuelling Is Not Optional

Low energy availability is common, often unintentional, and entirely addressable. The body does not perform well when it is periodically rewarded with food. It performs well when it is consistently fuelled.

If any of this sounds familiar, start by auditing what you eat around training. Track your intake for a week. Look at whether you are eating before and after every session. That single habit change is often where the improvement begins.

If you want a practical, nutrient-dense option for fuelling around training, explore Whole Supp's Superfood Meal Shake: Informed Sport Certified, gluten-free, and developed around 30 vitamins and minerals.