What is RED-S?
RED-S (Relative Energy Deficiency in Sport) is the situation in which the energy an athlete takes in is not enough to meet the needs of both training and the body’s basic functions. In children and adolescents, the energy need of growth is added on top of this. The problem does not necessarily have to be “eating little” or an eating disorder; often the child, without realising it, simply does not eat enough relative to the rising training load. The root problem is not intention but energy imbalance.
This concept was once defined only in girls as the “athlete triad” (loss of periods, low bone density, low energy), but RED-S is treated as the version of this that affects both girls and boys and covers a much wider array of systems.
What does it affect?
When there is not enough energy, the body directs scarce resources to priority functions and cuts back on some processes. This can create a wide range of effects: slowing of growth and delay of puberty; weakening of bone health (a rise in stress-fracture risk); hormonal changes and, in girls, periods becoming irregular or stopping; weakened immunity and frequent illness; and, paradoxically, a drop in performance. In other words, restricting energy, even if it brings short-term “lightness”, undermines development and performance.
In children and adolescents the most worrying effects are on growth and bone health; this period is the critical window in which most of the bone mass and height that last a lifetime are gained. For this reason, RED-S is a matter to be taken seriously in children’s sport.
Warning signs
RED-S can be insidious, but some signs are striking: in girls, periods being delayed, becoming irregular or stopping; recurrent injuries, especially stress fractures; unexplained slowing of growth or percentile; constant fatigue and an inability to recover; performance plateauing or dropping; frequent illness; and anxious attitudes toward food or body image. When several of these signs appear together, energy balance should be questioned.
Menstrual irregularity, especially, is often one of the earliest and clearest warnings, and should never be brushed off as “normal because she is an athlete”. Likewise, recurrent stress fractures may be a sign of an underlying energy deficiency.
Approach and prevention
The core solution to RED-S is to restore energy availability: that is, to raise energy intake to a level that meets the needs of training and growth. This usually requires not restriction but adequate, balanced nutrition. Because the matter is delicate and can affect growth, suspected RED-S should be assessed by a doctor and, where needed, a dietitian experienced in sports nutrition.
The key to prevention is always handling nutrition with a focus on health and energy, and avoiding pressure about weight or appearance. Remembering that as training load rises, nutrition must rise accordingly, carrying out regular growth and health monitoring, and taking warning signs seriously are protective. In the young athlete the priority is always healthy growth; performance is its natural result.