RED-S in Athletes: What Every Coach, Dietitian & Athlete Needs to Know

What Is RED-S?

Relative Energy Deficiency in Sport (RED-S) is a condition that occurs when athletes don’t consume enough energy (calories) to support the demands of training and everyday physiological functions. It affects performance, long-term health, and can impact both male and female athletes.

Initially understood as the Female Athlete Triad, RED-S has now evolved to include a wide range of body systems beyond just reproductive and bone health.

How Common Is RED-S in Athletes?

A 2021 study involving 112 elite and pre-elite female athletes found that 80% reported symptoms of RED-S. The most affected systems included:

Gastrointestinal (47%) Psychological (45%) Immunologic (38%) Hematologic (27%)

This data shows RED-S is not rare—and often goes unrecognised.

The Multisystem Impacts of RED-S

Nausea, bloating, constipation, and loss of appetite are frequently reported. These may result from slowed digestion due to LEA or changes in the gut microbiota.

  1. Iron Deficiency & Hematologic Effects

RED-S is commonly associated with iron deficiency anemia (IDA), due to a combination of inadequate intake, inflammation, and increased losses through sweat or menstruation. IDA contributes to fatigue, impaired oxygen delivery, and mood changes.

  1. Weakened Immune Function

Frequent colds, GI infections, and delayed wound healing may be signs of immune compromise due to low energy availability. Athletes in energy balance are shown to have better immune function, even under heavy training loads.

  1. Psychological Health

RED-S increases the risk of low mood, anxiety, and eating disorders. Athletes in judged, endurance, aesthetic, or weight-class sports are particularly vulnerable.

In female athletes, functional hypothalamic amenorrhea (FHA) can contribute to mood disruption. In males, RED-S often presents as excessive training or restrictive eating in pursuit of low body fat or increased muscle mass.

Why RED-S Is Often Missed

Despite its widespread impact, RED-S is frequently underdiagnosed. One study found only 33% of athletic trainers had heard of RED-S—even though nearly all had heard of the Female Athlete Triad.

Challenges in diagnosis include:

Lack of awareness among coaches and clinicians Absence of regular screening tools Athletes’ reluctance to report symptoms The IOC RED-S Clinical Assessment Tool (RED-S CAT) helps classify athletes into low, moderate, or high risk and can guide return-to-play decisions.

What Should Be Assessed?

When RED-S is suspected, a thorough clinical and physical evaluation is essential:

  • Growth trajectory & menstrual history
  • Mood changes, fatigue, performance decline
  • Recurrent injuries, illness, or stress fractures
  • Physical examination should include:
  • Vitals (heart rate, blood pressure)
  • Anthropometrics (height, weight, BMI)
  • Tanner staging for younger athletes
  • Lab tests (e.g., electrolytes, iron studies, hormones)
  • Additional investigations (e.g., ECG, DEXA scans)

Treatment: Restoring Energy Balance

The gold standard treatment for RED-S is restoring energy availability—either by increasing energy intake, decreasing training load, or both.

A multidisciplinary approach is best, including:

  • Sports physicians
  • Accredited dietitians
  • Psychologists or mental health professionals
  • Coaches and strength staff

Generally, increasing energy intake by 300–600 kcal/day is recommended. However, there is no standardised refeeding protocol, and care must be taken to avoid refeeding syndrome in severely undernourished athletes.

Is the Pill a Solution?

Some athletes are prescribed oral contraceptives for menstrual irregularities or low bone density. However, this is not always recommended:

They don’t restore natural hormonal cycles They may mask amenorrhea or FHA They can suppress IGF-1 and reduce bioavailable estrogen Transdermal estrogen + cyclic progesterone shows some promise for bone health, but it’s not a first-line treatment. Restoring energy balance remains the priority.

Final Thoughts

RED-S is a serious, often silent condition that affects athletes of all genders, ages, and levels. Left untreated, it can compromise performance, bone health, immune function, and mental wellbeing.

Early recognition, proactive screening, and a supportive team approach are key. Most importantly, athletes must be empowered to fuel for health, not just physique.

References: This blog was written using information solely from:

Dave SC, Fisher M. Relative energy deficiency in sport (RED - S). Curr Probl Pediatr Adolesc Health Care. 2022 Aug;52(8):101242. doi: 10.1016/j.cppeds.2022.101242. Epub 2022 Jul 30. PMID: 35915044.

Claudia Cramer