RED-S stands for Relative Energy Deficiency in Sport and is the impairment of many key physiological functions caused by energy deficiency.
Energy deficiency is also coined as Low Energy availability (LEA), which is a mismatch between energy intake (food consumption/portion sizes) and energy expenditure via physical activity and exercise. I.e. your calorie intake is nowhere near matching that amount of calories you’re burning through exercise.
Simply put, after the body has favoured energy provision for exercise, what’s left to maintain normal physiological functioning? When calorie intake is very low…not much.
When you have adequate energy available, you have ample amounts to cover exercise performance and optimal health. This is otherwise known as calorie maintenance, or meeting the bodies demands. Many athletes however wish to drop body fat which does mean there’s less energy available to meet the body’s demands.
The issue occurs when athletes go to the extreme and take their calorie intake too low. As a consequence, when LEA is prevalent, key processes such as the ones noted in the graphics become compromised.
Therefore, the question is; how low is too low?
RED-S is most common in female athletes; however recent data shows that many male athletes suffer too.
For females, it’s been noted that healthy physiological functioning can be found at a calorie intake of 45kcal/kg FFM (fat free mass), i.e. 2,340kcal for a 65kg female athlete with 20% body fat. However, the compromises in health and performance begins when they drop below 30kcal/kg FFM, which is 1,560kcal for the same 65kg female athlete (Loucks et al, 2003).
Exact cut off points for males is still somewhat unknown, but evidence from natural bodybuilders have found compromises ~20-25kcal/kg FFM. I.e. 1,520-1,900kcal for an 80kg guy with 5% body fat (Fagerberg, 2017).
Again, it’s difficult to give a cutoff point here for males, but it does appear that they can go lower calories before compromises are seen.
As it’s pretty difficult to test accurately for body fat % to know the amount of FFM you’re holding (i.e. the body weight that isn’t fat), this cut off point correlates quite nicely with your resting metabolic rate (RMR). So, if you’re an athlete who is training hard, it would be wise not to drop under your RMR calorie value.
As I always say, there’s going to be some form of trade off with any calorie restricted diets to shred body fat, but use the figures above as a rough guide to follow before these compromises gain too much fruition.
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