Research Says
Two recent studies examine aspects of Relative Energy Deficiency in Sport (RED-S). A systematic review by Alberto Valiño-Marques and colleagues (2024) analyzed RED-S effects across 308 male athletes in 10 studies, finding that low energy availability was associated with reduced metabolic rate in some athletes and elevated stress hormones in others. Complementing this, Dorota Langa and colleagues (2025) studied dietary patterns in 20 top-performing amateur female triathletes, discovering that those showing RED-S symptoms typically consumed more plant proteins and fiber but less saturated fat, despite similar total calorie intakes to healthy athletes. The triathlete study found RED-S risk markers in 30% of participants, while the systematic review reported prevalence rates in men varying from 15% to 70% across different studies.
Why It Matters
These studies reveal that RED-S manifests differently in male and female athletes, while highlighting how dietary composition—not just total calories—may influence RED-S risk. The findings suggest that certain dietary patterns, even those typically considered healthy, might affect energy availability and nutrient absorption differently among athletes. Understanding these nuances can help inform nutrition strategies that better support both health and performance.
Applied Insights
- Early warning signs of RED-S include decreased performance and reduced resting metabolic rate. Female-specific signs may include menstrual dysfunction, gastrointestinal symptoms, and increased risk of stress fractures due to potential impacts on bone health. Male-specific signs may include elevated cortisol, variable testosterone, and poor performance recovery.
- Athletes at risk of RED-S may benefit from moderating high-fiber foods and plant protein sources due to their effects on nutrient absorption and energy availability, while including adequate saturated fats as part of a balanced diet rather than relying heavily on unsaturated sources.
I’m Thinking
It’s great to see more research like these papers helping us understand the different nuances of RED-S in both female and male athletes. The female triathlete study raises interesting questions about whether current healthy eating trends might inadvertently increase RED-S risk in some athletes. The male athlete review challenges assumptions that bone and hormone effects mirror those seen in women. The bottom line is that RED-S may manifest differently in different athletes, highlighting the importance of considering a wide array of early warning signs and ensuring highly active athletes are fueling appropriately for their activity levels. Learn more about RED-S below.
Red-S Defined
RED-S (Relative Energy Deficiency in Sport) is what happens when athletes don’t consume enough calories to support both their training and their body’s basic functions. Think of it like trying to run your car without enough fuel — eventually, systems start shutting down to conserve energy.
When you train hard but don’t eat enough to match your activity level, your body enters an energy deficit. This isn’t just about being hungry — it’s about not having enough energy available for important processes like:
- Maintaining normal hormone levels
- Building and repairing muscle
- Keeping your metabolism running efficiently
- Supporting bone health
- Maintaining immune function
- Powering optimal athletic performance
RED-S can affect any athlete, regardless of gender or sport. While it was first recognized in female athletes (originally called the Female Athlete Triad), we now know that male athletes can develop RED-S too, though sometimes with different symptoms and thresholds.
- Warning signs might include:
- Decreased performance despite training hard
- Feeling fatigued more often than usual
- Taking longer to recover between workouts
- Changes in menstrual cycle (for women)
- Frequent injuries or illnesses
- Difficulty maintaining weight
- Mood changes
The key thing to understand is that RED-S isn’t just about eating too little — it’s about not having enough energy available to support both your training and your body’s basic needs. This can happen even if you’re eating what seems like a lot of food, especially if your training load is high or if your diet makes it hard to get enough easily-absorbed nutrients.
References
Langa, Dorota, Marta Naczyk, Robert K. Szymczak, Joanna Karbowska, and Zdzislaw Kochan. 2025. “A Preliminary Study of Nutrients Related to the Risk of Relative Energy Deficiency in Sport (RED-S) in Top-Performing Female Amateur Triathletes: Results from a Nutritional Assessment.” Nutrients 17 (2025): 208. https://doi.org/10.3390/nu17020208
Valiño-Marques, Alberto, José Manuel Jurado-Castro, Diego Domínguez-Balmaseda, Antonio Ranchal-Sánchez, Pedro Carrera-Bastos, Pablo Veiga-Herreros, Krizia Radesca Fabiano et al. 2024. “Relative Energy Deficiency in Sport (REDs) and Its Effect on Health and Performance in Men: A Systematic Review of Cross-Sectional Studies.” Research Square (2025). https://doi.org/10.21203/rs.3.rs-5571836/v1
