RED-S stands for Relative Energy Deficiency in Sport and is exactly what the name implies: a shortage of energy available to keep up with the demands of exercise, on top of essential daily functions (e.g. growth, respiration and digestion).

'Low energy availability’ describes the negative balance between energy intake and expenditure (i.e. food consumed vs physical exertion). The health and performance consequences of LEA can be severe, whether this occurs intentionally by means such as deliberate calorie restriction, or unintentionally by simply underestimating the energy demand of training or activity level. 

RED-S can affect any athlete or exerciser at any time, so it is crucial to be aware of the signs and symptoms and how to minimise risk.