Female runners and RED-S: low energy is not “not training hard enough”

What RED-S is

Relative Energy Deficiency in Sport (RED-S) describes the health and performance effects of chronic low energy availability. After exercise energy is subtracted, the remaining energy is insufficient to support normal physiology. It is not simply “eating too little”; it can occur in runners with high training loads, insufficient recovery or deliberate weight control.

The 2023 International Olympic Committee consensus updated the earlier female athlete triad framework, emphasising that RED-S can affect male and female athletes and involves endocrine, bone, metabolic, psychological and performance systems. It cannot be diagnosed from one blood test or one body-weight number.

Common signals

Female runners may notice menstrual changes, missed periods, recurrent stress fractures, persistent fatigue, poor sleep, feeling cold, digestive problems, low mood or declining performance. Men may experience reduced sex hormones, lower libido, reduced bone density and persistent fatigue. One symptom does not prove RED-S, but problems across several systems — especially with long-term low body weight, rapid weight loss or high training volume — deserve attention.

Do not treat amenorrhoea as a sign that training is “working”. Menstrual change may signal low energy availability, but it can also have gynaecological, endocrine or medication causes and needs medical assessment.

Do not solve it with more training or less food

When performance falls or these signals appear, the first response should not be to add training or restrict food further. Low energy availability is addressed through intake, training load, recovery and clinical assessment; eating less, adding cardio or relying on supplements can make it worse.

Nutrition recovery usually requires adequate carbohydrate and protein and a gradual return to energy availability and body weight; a doctor or registered dietitian should set the plan, especially with bone density, menstrual, eating-disorder or endocrine concerns. Psychological and eating-disorder support may also be part of care.

Pregnancy and postpartum

Running during pregnancy and after birth needs individual assessment. CDC pregnancy activity information encourages appropriate activity under medical guidance, but intensity, duration and contraindications depend on gestation, complications, delivery and recovery. Do not apply a pre-pregnancy pace or race plan directly. Seek urgent care for bleeding, abdominal pain, dizziness, chest pain, regular contractions or reduced fetal movement.

Scope and limits

This page does not diagnose RED-S, menstrual disorders, eating disorders or osteoporosis, and does not provide individual calorie, weight or training prescriptions. Persistent menstrual change, recurrent fractures, rapid weight change, loss of control around food or weight, or pregnancy/postpartum exercise concerns should be discussed with a doctor, registered dietitian or sports-medicine team.

Sources and scope

The definition of RED-S, the 2023 consensus update and its multi-system effects follow the International Olympic Committee RED-S consensus page; general pregnancy activity principles follow the CDC pregnancy activity page. RED-S requires clinical assessment and cannot be self-diagnosed from symptoms or device data. Checked 2026-10-28.