RED-S Relative Energy Deficiency: An Energy Supply Warning Sign for Female Athletes

From the “Female Athlete Triad” to RED-S

The “Female Athlete Triad,” proposed in 1992, identified three interrelated conditions: low energy availability / menstrual dysfunction / decreased bone mineral density. In 2014, the IOC expanded this concept into RED-S (Relative Energy Deficiency in Sport), encompassing broader effects on the endocrine, metabolic, cardiovascular, and immune systems, and affecting all genders.

Core Concept: Energy Availability (EA)

Energy Availability EA = (Daily Energy Intake - Exercise Energy Expenditure) / Fat-Free Mass (kg)

Example: A female triathlete weighing 60 kg with 20% body fat (fat-free mass 48 kg) burns 800 kcal in a day’s training.

• If she consumes only 2000 kcal: EA = (2000–800)/48 = 25 kcal/kg → Dangerous
• She needs to consume at least 2160 kcal to reach an EA ≥ 30
• To achieve an optimal EA of 45, she needs ≥ 2960 kcal

10 Often-Overlooked Warning Signs of RED-S

1. Menstrual cycle lengthening (>35 days) or amenorrhea (>3 months)
2. Frequent colds, slow wound healing
3. Stress fractures (especially tibia, metatarsals, sacrum)
4. Performance plateau or decline lasting more than 3 months
5. Persistently low resting heart rate (< 40 bpm)
6. Feeling cold, cold hands and feet
7. Hair loss, dry skin
8. Low mood, loss of training motivation
9. Gastrointestinal discomfort, constipation
10. HRV persistently below personal baseline

Affected Systems Overview

High-Risk Groups

• Endurance sports (marathon, triathlon, cycling climbing)
• Sports emphasizing leanness/lightness
• Periods of sharply increased training volume (pre-season)
• Those following vegan/low-fat/low-carb diets
• Athletes with perfectionism and high achievement motivation

Prevention and Treatment

Step 1: Confirm Your EA

Use 1–2 weeks of dietary logging plus Garmin/Polar training expenditure estimates to honestly calculate your EA.

Step 2: Replenish Energy

• Add 300–500 kcal on training days: Prioritize complex carbohydrates + protein
• Refuel within 30 minutes after training: 1.0 g/kg carbohydrate + 0.3 g/kg protein
• Don’t skip breakfast: Fasted training plus skipping breakfast is a fast track to RED-S for female athletes

Step 3: Restore Menstruation

From adjusting EA to the return of menstruation typically takes 3–6 months. The return of menstruation is a key indicator of RED-S recovery.

Step 4: Multidisciplinary Medical Team

Sports medicine physician, sports dietitian, gynecologist, psychologist. Don’t go it alone.

One-Sentence Summary

Eating enough isn’t indulgence; it’s a prerequisite for performance.

Related Reading

• Relative Energy Deficiency in Sport (RED-S) in Female Runners: Identifying the Risks and Prevention
• RED-S Relative Energy Deficiency: The Most Overlooked Health Breakdown in Endurance Athletes
• RED-S in Female Runners: Relative Energy Deficiency Is More Than Just Eating Less
• Relative Energy Deficiency (RED-S): The Most Dangerous Dietary Trap for Endurance Athletes