Relative energy deficiency in sport is a fairly new term that describes a mismatch between calorie intake by athletes and the calories they expend during training, leaving inadequate energy available to properly support bodily functions necessary for health and performance. Relative energy deficiency (RED-S) has been linked to weakened bones, low testosterone (male athletes), low estrogen (female athletes), higher levels of stress hormones, changes in resting metabolism, impaired immunity and menstrual disturbances.

Owing to the higher rates of energy expenditure in endurance athletes, such as runners, these individuals are at greater risk for suffering from low energy availability and associated health complications. They therefore require adequate education on the importance of meeting the caloric needs of training.

See also: Surprising Types (and Signs) of Eating Disorders in Athletes