Relative Energy Deficiency in sport (RED S) is a term describing the condition of the body where the balance between the dietary energy intake is lower than energy expenditure. With other words, one does not manage to ingest enough energy to meet the daily energy requirements. These requirements stand for the expended energy through basal metabolic rate, non-exercise activity thermogenesis (such as walking, shopping, cleaning etc.), exercise and thermic effect of food.
In RED S either the intake is too low, or the expenditure is too high. For example, because cyclists burn so many calories during the Tour de France, they must have their diet planned in that way, that it forces them to eat enough to meet the requirements and thus avoid low energy availability. These cyclists are a good example of how stress and high training loads can have a negative effect on appetite. Loss of appetite is only one factor leading to involuntary low energy availability, others might include gastro-intestinal pathologies (celiac disease, IBD etc.), incorrect nutrition planning and lack of knowledge about nutrition. Voluntary dietary factors, on the other hand, are intentional weight loss, eating disorders/disordered eating, fasting, poor food choice/malnutrition.
Energy deficiency prevents homeostasis on many levels and negatively affects numerous physiological functions ultimately negatively impacting menstrual function, bone health as well as immunological, gastrointestinal, psychological, cardiovascular and endocrine function. Subjects of both sexes with RED S might experience an altered sex hormone profile and with it associated problems (hypothalamic amenorrhea, low testosterone), decreased basal metabolic rate, impaired thermoregulation, problems with digestion, decreased bone mineral density, recurrent illnesses, mood disorders (anxiety/depression, irritability), changes in heart rate, increased cortisol and other health-related problems. These manifestations lead to reduced performance, longer times to finish, reduced muscle strength, disturbed coordination and concentration, increased injury risk (stress fractures, overuse injuries) and decreased response to training, resulting in slower or no performance improvement.
So the solution is simply to eat more?
Well, no! We must improve the function of the hypothalamus-pituitary axis, which controls our metabolism, thermoregulation, reproduction etc. Therefore, several behavioural changes must be made to curb up the suppressed axis. A good start is to reduce physical and psychological stress, increase energy intake and decrease the activity levels. This must be done under supervision and is very individual. In women, we can pretty accurately determine the sufficient energy intake in the correlation to menstrual function, which is very easy to follow. Several intervention studies have shown success and the recovery of menstrual function with a significant increase in caloric intake over a longer period of time and exercise modification.
Okay, I need to eat more, but more fat or more carbohydrates?
Sex hormones are steroid hormones derived from cholesterol. Based on that one would think: “if I eat more fat and cholesterol, my hormone levels will rise, and I will recover my cycle”. It is true that low fat intake can be detrimental, and we need some essential amount of fat in our diet. However, our region in the brain- hypothalamus, regulates body energy homeostasis and senses energy and nutrient availability. It senses both glucose and fats as well as insulin, leptin and other signals of hunger and satiety. Restricting energy and nutrient intake through both extreme diets low carb high fat (keto diet) and high carb low fat can lead to reduced sex hormone levels, as the signals are missing in the hypothalamus. Therefore, we must ensure enough of both, carbohydrates and fats, to stimulate the hypothalamus. How much is enough then? We can determine you an exact amount based on your current weight/BMI and activity levels, but one thing is certain, only high energy availability and caloric surplus will result in regaining your menstrual cycle and resolving REDs symptoms.