STUDY THE SCIENCE

What is Energy Availability (EA)?

Energy Availability isn't just counting total calories; it measures the energy left over for your body’s baseline health after subtracting the calories you burn during exercise.

Energy Availability = Dietary Energy Intake (kcal) − Exercise Energy Expenditure (kcal) ​/ Fat-Free Mass (kg) 

• Optimal Energy Availability (≥45 kcal/kg FFM/day): Your body has enough fuel for full health, tissue repair, growth, and peak athletic performance.

• Low Energy Availability (<30 kcal/kg FFM/day): According to research published in the Journal of Sports Sciences by Dr. Anne Loucks, falling below this threshold triggers protective biological changes, slowing down your metabolism and hormone production to conserve energy.

The Biological Triage

According to the International Olympic Committee (IOC) 2023 REDs Consensus Statement, when energy intake drops below your total needs, your brain prioritizes immediate survival tasks over long-term health and athletic performance.

System-by-System Science

1. Hormones & Reproduction

• What Happens: The brain's hypothalamus slows down the release of signaling hormones (LH and FSH).

• The Science: According to the Female Athlete Coalition Consensus Statement (published in the British Journal of Sports Medicine), this disruption stops normal menstrual cycles in female athletes and lowers testosterone levels in male athletes, directly impacting muscle recovery, power output, and mood.

2. Bone Density & Fracture Risk

• What Happens: Bone tissue is constantly being broken down and rebuilt. Rebuilding requires both adequate energy and balanced sex hormones (estrogen and testosterone).

• The Science: According to clinical research led by Dr. Adam Tenforde in Sports Medicine, prolonged low energy availability causes bone breakdown to outpace bone formation, leading to early loss of bone density and a higher risk of stress fractures in both male and female endurance athletes.

3. Metabolic Rate & Temperature

• What Happens: The body lowers its Resting Metabolic Rate (RMR) to stretch every calorie as far as possible.

• The Science: According to findings in the Journal of Clinical Endocrinology & Metabolism, low energy availability causes active thyroid hormone (T3​) levels to drop. This leads to symptoms like chronic cold sensitivity, uncharacteristic sluggishness, and difficulty building lean muscle mass despite heavy training.

4. Immune Function & Soft Tissue Repair

• What Happens: Protein synthesis and cellular repair get deprioritized to save calories for basic organ function.

• The Science: According to guidelines from the American College of Sports Medicine (ACSM), energy deficits impair muscle protein synthesis and slow down immune defense mechanisms, leading to lingering muscle soreness, frequent minor illnesses (like colds), and slow wound healing.

Prevalence & Risk Across Sports

• Female Athletes (Overall): Studies show the prevalence of low energy availability ranges from 23% to 80% depending on the sport. (Source: Mountjoy et al., 2023 IOC Consensus Statement on REDs, British Journal of Sports Medicine)

• Male Athletes (Overall): Research estimates that 15% to 70% of male athletes experience periods of low energy availability, with the highest rates in endurance and weight-category sports. (Source: Tenforde et al., 2016, Sports Medicine)

• High-Risk Sport Categories: In aesthetic sports (e.g., gymnastics, figure skating, dance) and weight-class/endurance sports (e.g., running, cycling, rowing), screening tests show that 67% to 74% of female athletes and 26% to 51% of male athletes fall into medium-to-high risk zones for REDs. (Source: ACSM Expert Consensus Statement, 2021, Current Sports Medicine Reports)

Clinical Outcomes & Health Impacts

• Bone Health & Injuries: Athletes with chronic low energy availability face a 15% to 30% lifetime rate of stress fractures, with a significantly higher risk for recurrent bone stress injuries. (Source: Nattiv et al., ACSM Position Stand)

• Menstrual Dysfunction: Primary or secondary amenorrhea (missing 3+ consecutive periods) affects 20% to 60% of female athletes in high-demand endurance and aesthetic sports, compared to roughly 2% to 5% in the general population. (Source: De Souza et al., 2014 Female Athlete Coalition Consensus Statement)

• Disordered Eating Drivers: Subclinical disordered eating or intentional restrictive feeding drives low energy availability in 6% to 45% of female athletes and 1% to 19% of male athletes. (Source: Sundgot-Borgen & Torstveit, 2004, Clinical Journal of Sport Medicine / NCAA Sport Science Institute)