Relative energy deficiency in sport, or RED-S, is a medical condition caused by chronic underfueling relative to exercise and physiological demands. A 2026 study in the Journal of Science and Medicine in Sport reported that 70 percent of high-level female athletes are at risk, with Emma Navarro recently sharing her three-year struggle with the condition on Instagram.
In Plain English: The Clinical Takeaway
- Low Energy Availability: This occurs when an individual fails to consume enough calories to support both daily bodily functions and athletic training.
- Systemic Impact: Chronic underfueling can affect almost every system in the body, including hormonal pathways, the immune system, and bone mineral density.
- Recovery Timeline: While mild underfueling triggers acute hunger within a day, fully reversing the condition can require six to nine months.
The Physiological Mechanisms Behind Relative Energy Deficiency
The human body relies on a precise balance of energy intake to sustain basal metabolic rate, cellular repair, thermoregulation, and physical exertion. According to Elizabeth Matzkin, MD, an orthopedic surgeon and chief of women’s sports medicine at Brigham and Women’s Hospital, the body slows down non-essential systems to save fuel whenever energy availability continuously falls short of these basic physiological requirements.
Amy West, MD, a sports medicine physician at Northwell Orthopedic Institute, notes that short-term manifestations include diminished muscular strength, impaired endurance, frequent illness, and psychological symptoms such as anxiety and depression. Over extended periods, particularly during adolescence and young adulthood when peak bone mass is established, this energy deficit significantly increases the lifetime risk of developing osteoporosis. Meanwhile, missing your period for long periods of time can have impacts on future fertility, Dr. West adds.
Vulnerability Factors and the Historical Shift from the Female Athlete Triad
Historically recognized until 2014 as the “female athlete triad”—a syndrome highlighting the relationship between undereating, menstrual dysfunction, and decreased bone mineral density—the broader classification of RED-S acknowledges that the condition affects all biological systems and can occur in any athlete. However, female athletes are more vulnerable, especially in sports that emphasize leanness, endurance, aesthetics, or weight categories such as running, gymnastics, and diving. Societal pressures regarding body composition and a higher statistical prevalence of diagnosed eating disorders further elevate this risk.
Emma Navarro publicly detailed her experience with RED-S on Instagram, citing symptoms that included extreme mood swings, brain fog, a weakened immune system, constant headaches, dizziness, and unrelenting hunger. Her experience underscores that elite competitors are just as vulnerable to chronic underfueling as other athletes.
| Stage of RED-S | Primary Clinical Indicators | Affected Physiological Systems |
|---|---|---|
| Early Low Energy Availability | Persistent fatigue, delayed recovery, sleep disturbances, increased hunger | Endocrine, Central Nervous, Musculoskeletal |
| Moderate Progression | Recurrent infections, declining athletic performance, mood swings, weight loss | Immune, Metabolic, Psychological |
| Advanced RED-S | Irregular or absent periods, stress fractures, persistent bone or limb pain | Reproductive, Skeletal, Cardiovascular |
Preventing and managing RED-S does not require obsessive macro-tracking or calorie counting. Amy Stephens, RD, a sports dietitian specializing in eating disorders, advocates for intuitive fueling centered on consistent meal frequency. This includes consuming three meals daily, composed of approximately one-third protein, one-third carbohydrates, and one-third vegetables.
Should any health markers fall outside the normal range, insufficient fuel could be the culprit, though those results must be evaluated alongside your overall medical history and any additional diagnostic tests by your physician.
Contraindications & When to Consult a Doctor
Professional medical evaluation is indicated when symptoms transition from general fatigue to clinical red flags such as stress fractures or localized bone pain. Treating established RED-S requires a multidisciplinary intervention plan supervised by doctors and dietitians to safely restore energy balance.
References
- Journal of Science and Medicine in Sport: Prevalence of RED-S in High-Level Female Athletes
