Female Athlete Triad and RED-S: Energy, Hormones, and Bone

A Problem That Affects Male and Female Athletes Alike — But Kills Female Bones Faster

In 2014, the International Olympic Committee published a landmark consensus statement expanding the Female Athlete Triad — a clinical syndrome of low energy availability, menstrual dysfunction, and low bone mineral density — into a broader framework called Relative Energy Deficiency in Sport (RED-S). The original Triad, described by the American College of Sports Medicine in 1992, captured a real phenomenon but missed large populations: male athletes, non-binary athletes, and female athletes who showed metabolic consequences of energy deficiency without the classical triad of all three features. RED-S encompasses over 30 health and performance outcomes driven by one root cause: the body receiving insufficient energy to fund both physiological function and athletic training demands.

Energy Availability: The Central Calculation

Energy availability (EA) is the energy remaining for physiological processes after accounting for exercise energy expenditure:

EA = (Energy Intake — Exercise Energy Expenditure) ÷ Fat-Free Mass (kg)

An EA of 45 kcal/kg fat-free mass (FFM)/day is considered optimal for most physiological functions. Impaired physiological function begins to appear below 30 kcal/kg FFM/day. Acute suppression of pulsatile luteinizing hormone (LH) — the first detectable hormonal signal of energy deficiency — occurs within five days of sustained EA below 30 kcal/kg FFM/day, as demonstrated by Loucks and Thuma (2003) in controlled laboratory conditions.

Athletes often unknowingly reach low EA states. Intentional dietary restriction accounts for only some cases; many result from inadequate fueling during training volume increases, poor sports nutrition knowledge, or disordered eating patterns that fall below clinical eating disorder thresholds.

The Hormonal Suppression Cascade

Low energy availability signals the hypothalamus to suppress gonadotropin-releasing hormone (GnRH) pulsatility — the same mechanism that preserves energy in famine conditions. The result is reduced FSH and LH secretion, leading to anovulation and menstrual irregularities ranging from luteal phase deficiency to oligomenorrhea (<6 cycles/year) to functional hypothalamic amenorrhea (FHA, complete cessation of menses for >3 months in the absence of structural pathology).

FHA is present in:

• 65 percent of competitive distance runners
• Up to 60 percent of ballet dancers
• 30–40 percent of competitive road cyclists
• Approximately 25 percent of gymnasts

Thyroid hormone metabolism also shifts: T3 (active thyroid hormone) declines and reverse T3 (metabolically inactive) rises in low EA states, reducing resting metabolic rate as an adaptive response. Growth hormone increases but IGF-1 (its mediator) falls — another paradox of energy conservation. Cortisol rises with chronic LEA, further suppressing reproductive hormones and impairing immune function.

The Bone Stress Injury Cascade

Estrogen, produced primarily by ovarian follicles, exerts a powerful protective effect on bone by inhibiting osteoclast activity and supporting osteoblast survival. When FHA eliminates ovarian estrogen production, bone resorption accelerates. Young athletes in their peak bone mass accrual years (ages 12–25) who develop FHA may fail to reach their genetic bone density potential — a deficit that persists permanently.

The clinical consequence is bone stress injuries (BSIs): stress reactions progressing to stress fractures. The pelvis, femoral neck, metatarsals, and tibia are highest-risk sites. BSIs in athletes with FHA recur at rates three to four times higher than in eumenorrheic athletes and heal significantly more slowly. The tibia is the most common site; femoral neck stress fractures are the most dangerous, carrying risk of complete fracture and avascular necrosis if not recognized early.

• Female distance runners with FHA have 2–4 times higher BSI rates than those with regular menses.
• Each year of FHA is associated with an approximately 2–3 percent reduction in lumbar spine bone mineral density — matching the rate of loss in postmenopausal women.
• Bone mineral density may not fully recover even after menstrual function returns, depending on duration of amenorrhea.

RED-S: The Expanded Framework

The 2014 IOC RED-S framework documents consequences extending well beyond the reproductive-bone axis:

Clinical Management

The primary intervention for RED-S is increasing energy availability — specifically, increasing caloric intake and/or reducing training load. Even a 300–500 kcal/day increase can restore LH pulsatility within weeks in controlled settings. Oral contraceptives do not restore bone mineral density in athletes with FHA (the estrogen dose is insufficient and does not address the underlying energy deficit) and are not recommended as the primary intervention by the 2014 or 2022 IOC updates.

Multidisciplinary management — sports medicine physician, registered sports dietitian, and sports psychologist — is the evidence-based approach for clinical RED-S. Athletes with documented eating disorders require primary psychiatric treatment before returning to full training.

This article is for informational purposes only. Consult a qualified healthcare professional.