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Relative Energy Deficiency in Sport (RED-S): The Risks of Under Eating

Relative Energy Deficiency in Sport (RED-S): The Risks of Under Eating

Heavy and intense training schedules, reduced sleep, fussy eating habits and poor nutrition all combine together to put youth athletes at an increased of Relative Energy Deficiency in Sport, or RED-S as it’s more commonly known. But what exactly is RED-S and why is it so important for youth athletes to eat enough? We take a look at the risks and causes of RED-S and how youth athletes can avoid this condition and the impact it can have on growth, health and performance.

What is RED-S?

RED-S is a condition caused when an athlete does not consume enough calories (eat enough food) to match the high calorie demands the body must use for exercise. This then means that there is not enough energy left over for the normal processes of growth and development within the body which are key to health [1].


Simply put: if energy intake is lower than energy expenditure then the body is in a state of low energy availability.


Think of this like when your phone goes into low power or battery saver mode. Certain features and functions will no longer run until the phone is charged again. The body works in the same way. The energy from food will be used for exercise costs first and if there is not enough left over, then the body will start to switch off some of its vital processes, or they will be down regulated and effectively run slower.


What does this mean?

Being in a state of low energy availability is hugely concerning for youth athletes. It will affect a range of the body’s functions from health and growth, such as causing weaker bones and increasing the risks and occurrence of fractures and breaks to affecting hormonal production, lowering immunity, causing nutrient deficiencies and in severe cases it can affect the heart [1]. This is all as well as massively impacting performance, through impairing recovery, causing fatigue and increasing injury risk [2].


Signs and Symptoms to watch out for:

  • Weight loss/ being underweight
  • Periods stopping/ becoming irregular
  • Recurrent illnesses e.g. colds and flu’s
  • Decreased sports performance
  • Mood changes and swings
  • Increased or excessive fatigue
  • Delayed or disordered growth and development 

Who can RED-S affect?

It was first thought to only affect the female athlete, when low dietary intake was discovered to cause a loss of the menstrual cycle and affect bone health [3]. However, since then, lots more research has be done and it is now known to be a concern for both male and female athletes of all ages [2] and is particularly concerning for youth athletes who require a lot of additional energy for normal growth and development and for their sporting schedules.


It can occur when athletes intentionally restrict their eating for either body composition purposes or as a result of disordered eating, or it can happen unintentionally when there is a simply a mismatch between the amount eaten and energy used for sport [1].

How can RED-S be avoided?

The simple answer to this question is to ensure athletes are eating enough. However, the exact number of calories to be consumed is much more complicated and will depend on a number of things including age, gender, activity level etc, but this will be higher than kids and teens of a similar age who don’t play regular sport.


Ensuring athletes are eating 3 full meals and 2 snacks per day and getting a balanced and varied diet is a great start to ensuring they eat enough to avoid RED-S and the negative effects [4]. Take a look at our other blogs to learn all about how to properly fuel before and refuel after a training session to help and avoid RED-S. Not sure if you're eating enough? This article might be useful to help you recognise the signs of undereating.


Young athletes should certainly be encouraged to pursue their sporting careers, however, parents and the athletes themselves must be aware of how to adequately fuel such demanding sports schedules. First and foremost, athletes must be eating for growth and health, and after that, fuelling for performance. Making sure this happens will ensure they have a healthy, successful and long career!

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Disclaimer: This article is intended to provide general information about nutrition for youth athletes and is not meant to replace professional dietary advice or individual nutritional counselling. Every child's nutritional needs can vary due to factors such as age, size, physical activity level, and medical conditions. We strongly recommend consulting with a registered dietitian or a healthcare provider before making changes to your child's diet, such as adding supplements and food powders. YSN and the author of this article do not take responsibility for any possible consequences from any treatment, procedure, dietary modification, action, or application of medication which results from reading or following the information contained in this article


  1. Loucks, A.B., Kiens, B. and Wright, H.H. (2011) Energy availability in athletes. Journal of sports sciences, 29 (sup1), S7-S15.
  2. Mountjoy, M., Sundgot-Borgen, J., Burke, L., Carter, S., Constantini, N., Lebrun, C., Meyer, N., Sherman, R., Steffen, K., Budgett, R. and Ljungqvist, A. (2014) The IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport (RED-S). British Journal of Sports Medicine, 48 (7), 491.
  3. Loucks, A.B. and Thuma, J.R. (2003) Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. The Journal of Clinical Endocrinology and Metabolism, 88 (1), 297-311.
  4. Purcell, L. (2013) Sport nutrition for young athletes. Paediatrics & Child Health, 18(4), pp. 200-202.


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