Underlying Factors of REDs

The concepts of energy availability (EA) and low energy availability (LEA) are fundamental to the definition of REDs. 

Energy availability is defined as the amount of energy available to the body for essential function, after accounting for expenditure during exercise or training (1). Essential function includes, but is not limited to: 

  • Digestion

  • Cardiac function

  • Cognitive function 

  • Muscle repair

  • Immune strength

  • Maintenance of bone health

  • Hormone production

Energy intake is any calorie ingested in any form. When energy intake does not keep up with expenditure from exercise, there is insufficient energy for essential functions. This state where the demands of essential function are not met is called low energy availability (1).

Energy availability can be thought of as the balance between the energy you use and the energy you consume.

Causes of REDs

Low energy availability can arise in many different ways. Common causes include, but are not limited to:

  • A failure to adjust energy intake according to changes in training load, deliberately or by accident.

  • A medical condition such as anorexia nervosa or another clinical eating disorder, or a condition involving disordered eating (2).

Signs and Symptoms of REDs

Low energy availability often results in changes in bodily system functioning that are critical to health and athletic performance. The effects of energy imbalances have been shown to exist on small time scales (within same-day energy balance) (3), as well as to persist over longer periods of time (2,4). Please note that REDs affects everyone differently, and individuals may not experience all of the symptoms listed below.

Physical Signs

  • Unexplained fatigue and lack of energy

  • Weight loss

  • Frequent illness

  • Recurrent injuries

  • Decreased sport performance

  • Decreased response to training stimulus

  • Low libido or change in menstrual function

  • Disruptions to puberty 

  • Difficulty maintaining warm body temperature

  • Iron deficiency

Psychological Signs

  • Depression

  • Increased irritability 

  • Decreased concentration 

  • Decreased Coordination

  • Impaired judgment

  • Desire to skip rest days

  • Drive for thinness

  • Avoidance of meals or food groups

  • Feeling the need to “earn one’s food”

  • Body dysmorphia

  1. Loucks AB, Kiens B, Wright HH. Energy availability in athletes. J Sports Sci 2011;29:S7–15.

  2. Mountjoy M, Sundgot-Borgen J, Burke L, et al The IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport (RED-S) British Journal of Sports Medicine 2014;48:491-497.

  3. Fensham, N.C., Heikura, I.A., McKay, A.K., Tee, N., Ackerman, K.E. and Burke, L.M. Short-Term Carbohydrate Restriction Impairs Bone Formation at Rest and During Prolonged Exercise to a Greater Degree than Low Energy Availability. J Bone Miner Res. 2022

  4. Mountjoy M, Sundgot-Borgen JK, Burke LM, et al IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update British Journal of Sports Medicine 2018;52:687-697.