If you subtract the energy you expend in exercise from the energy you take in, then what you are left with should be enough to maintain health and reproductive function (for women), and for a young person there should also be enough for growth. If you don’t have enough left over this is called ‘low energy availability’ which underlines the condition ‘RED-S’ (relative energy deficiency in sport). RED-S is a condition whereby a person is not getting enough calories to maintain all the functions needed for good health (e.g. immune health, protein synthesis, bone health etc.). As a result, the body will go into ‘survival’ mode and start to cut back in places. For example, metabolic rate will be lowered and for women periods can stop (as this also requires energy!). The breaking down of bone will also be greater than bone building, which increases the risk of stress fractures. RED-S describes the effects of having energy deficiency on a wide range of body processes. This can impact both women and men across all levels from elite athletes to more recreational (e.g. runners, gym goers etc.)
Things that might lead to low energy availability
- Knowingly or unknowingly reducing calorie intake
- Restricted eating and overtraining
- Dieting whilst still maintaining high levels of training
- Cutting out whole food groups (e.g. carbohydrate, protein, fat) – which we need for brain health, immunity, bone health, optimal performance, and recovery. Eliminating food groups also means important micronutrients can be reduced (e.g. iron, B-vitamins, calcium) which we need to metabolise the macronutrients (carbohydrate, protein, fat), and for god health all round.
How do you know if you are getting enough energy to meet your energy demands?
Energy availability is energy intake minus exercise energy expenditure. It is considered that optimal energy availability is around 45 kcal per kg fat free mass. Low energy availability is classed as less than 30kcal per kg fat free mass. However, most people would be unlikely to calculate their own needs, and so the following are some signs and symptoms.
What are the signs and symptoms of low energy intakes in active people?
Although weight loss can be one sign that energy availability is low, body weight is not always a true reflection of energy availability. For example, a person could have a healthy body weight yet still have insufficient energy intakes. This can partly be related to the lowered metabolic rate from restricted energy, so body weight may not be lowered. Some other signs might include:
- Exercise associated menstrual dysfunction (which can lead to further health problems such as poor bone health)
- Frequent injuries
- Frequent illness
Questions you can ask yourself:
- Do you feel that you are fuelling adequately for your exercise and training?
- Do you have rest days, or is there are a chance you are overtraining?
- Have your periods stopped? (*If they have it is very important to see a GP)