Functional testosterone deficiency in relative energy deficiency in sport

Relative energy deficiency in sport (REDs) is a syndrome describing dysfunction in normal physiology related to the term "negative energy availability" because of a mismatch between energy consumption and expenditure in sport. A disruption of the hypothalamic-pituitary-testes axis, resulting in testosterone deficiency, seems like the dominant feature in males. REDs-associated testosterone deficiency is functional, and treatment should aim towards reducing training and increasing energy consumption, as argued in this review. Testosterone treatment should not be initiated.