Relative Energy Deficiency in Sport (REDs)

A syndrome of impaired physiological and psychological functioning caused by prolonged or severe low energy availability (LEA) — energy intake insufficient for training demands plus normal bodily function. Affects adolescent and adult athletes of both sexes; males appear more resilient to the effects of low energy availability than females, though not immune.

The term replaced and broadened the older female athlete triad (low energy availability, menstrual dysfunction, low bone mineral density), which is still useful shorthand for the female presentation.

Energy availability

Energy availability = energy intake minus exercise energy expenditure — the calories left for biological processes once the cost of the sport is subtracted. Sustained low EA, usually taken as under 30 kcal/kg fat-free mass, or repeated within-day bouts in very lean people, causes the impaired physiological functioning that defines REDs.

Low intake is often unintentional. Many athletes without a diagnosable eating disorder still eat well below their needs, and the sport’s own culture around body composition drives it. Where the deficit is deliberate, it is an eating disorder — female athletes are 5 to 10 times more likely than male athletes to have one.

Who is at risk

Any athlete at any level, but especially:

• Endurance sports — distance running, swimming, rowing, cycling
• Aesthetic and subjectively judged sports — gymnastics, figure skating, dance
• Weight-class sports

Effects

REDs impairs metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health, plus growth and development in youth athletes.

Bone. The impact on bone is pronounced and fast, particularly in women, via both oestrogen-dependent and oestrogen-independent mechanisms. As little as five days of low EA impairs bone protein synthesis and mineralisation, so dietary correction should not wait. Athletes should have bone mineral density 5-15% above age-matched non-athletes; falling short raises fragility and fracture risk. Stress fracture incidence is higher in amenorrhoeic athletes, and bone density correlates negatively with the number of missed cycles since menarche.

Menstrual. Dysfunction arises from altered hypothalamic function and low oestrogen — primary or secondary amenorrhoea, or oligomenorrhoea. In female athletes an irregular or absent cycle is the most obvious clinical marker of insufficient energy availability.

Iron. Depleted iron stores affect roughly 15-35% of female and 3-11% of male athletes.

Assessment

Take a focused history covering nutrition and eating patterns, menstrual history, endocrine and family history, psychosocial history including eating patterns and mood, change in performance, and all medications, supplements, contraceptives, diet pills and laxatives.

On examination look for thyroid enlargement, dental erosion and parotid hypertrophy from vomiting, and visual field loss suggesting a pituitary macroadenoma.

Screening questionnaires: LEAF-Q (female athletes) or LEAM-Q (male athletes).

Bloods to consider: FBC, iron studies, glucose, lipids, LH/FSH/oestradiol/ progesterone/testosterone, prolactin, TSH/T4/T3, cortisol, IGF-1/GH, and beta-hCG if amenorrhoeic. Falling testosterone or oestrogen, low T3, or a rise in cortisol are supportive hormonal markers, but there is no absolute threshold of low energy availability that produces amenorrhoea in women or low testosterone in men — the diagnosis stays clinical.

Imaging: plain radiograph first if a stress fracture is suspected, bone scan if negative, and DXA in athletes with multiple stress fractures or to assess for osteopenia.

Return to play

The RED-S Clinical Assessment Tool grades risk as a traffic light: red = cease participation, yellow = compete with medical clearance and train under supervision, green = full participation.

Management

Multidisciplinary — sports physician, dietitian and psychology. Treatment is correction of the underlying energy deficit, by increasing intake, reducing training load, or both, with dietitian involvement. Most consequences reverse with adequate treatment, but bone and growth effects may not fully recover without timely intervention.