RED-S and the Female Athlete Triad: When Underfueling Damages Your Body

Many athletes think eating less will make them faster, leaner, and more competitive. In reality, chronic underfueling triggers a cascade of health problems that ultimately destroy both performance and long-term health.

Relative Energy Deficiency in Sport (RED-S)—and its predecessor, the Female Athlete Triad—are serious conditions that affect far more athletes than most people realize.

What Is RED-S?

RED-S (Relative Energy Deficiency in Sport) occurs when an athlete doesn't consume enough calories to support both their exercise demands and basic bodily functions.

The body needs energy for:

Exercise and training
Basic metabolism (breathing, digestion, brain function)
Immune function
Hormone production
Bone maintenance
Tissue repair
And much more

When energy intake is too low relative to expenditure, the body starts shutting down "non-essential" functions to conserve energy. The problem: functions that seem non-essential in the short term are critical for long-term health.

The Female Athlete Triad

Before RED-S was defined, researchers identified the "Female Athlete Triad" in women:

Low energy availability (underfueling)
Menstrual dysfunction (irregular or absent periods)
Low bone mineral density (weakened bones)

These three components are interconnected. Low energy triggers hormonal changes that disrupt menstruation and weaken bones.

Why RED-S Replaced "Triad"

RED-S expanded the concept because:

Men are affected too. They experience similar hormonal and bone consequences.
The effects go beyond three areas. Nearly every body system is impacted.
It's a spectrum. You don't need all three triad components to have a problem.

RED-S recognizes that underfueling harms everyone, not just female athletes.

Who's at Risk?

RED-S is most common in:

Sports Emphasizing Leanness

Running (especially distance)
Cycling
Swimming
Gymnastics
Figure skating
Dance
Rowing (weight-class)
Wrestling (weight-class)
Bodybuilding/physique sports

Athletes With:

Restrictive eating patterns
History of eating disorders
Pressure to lose weight for performance
High training volumes
Perfectionist personalities
Coaches who emphasize weight

All Genders

Men are increasingly recognized as affected, though they may present differently (testosterone decline rather than menstrual disruption).

The Cascade of Problems

Underfueling creates problems throughout the body:

Hormonal Dysfunction

In women:

Irregular or absent periods (amenorrhea)
Low estrogen levels
Reduced fertility
Hormonal symptoms (mood changes, sleep issues)

In men:

Low testosterone
Reduced libido
Erectile dysfunction
Mood changes

In both:

Elevated cortisol
Disrupted thyroid function
Growth hormone issues

Bone Health

Low energy availability devastates bones:

Decreased bone formation
Increased bone breakdown
Stress fractures (often the first warning sign)
Early osteoporosis
Permanent bone density loss if prolonged

Athletes with RED-S have bone density more typical of elderly individuals—in their 20s.

Metabolic Suppression

The body slows metabolism to conserve energy:

Lower resting metabolic rate
Reduced body temperature
Fatigue and lethargy
Difficulty losing fat (paradoxically)
Weight regain when eating normalizes

Cardiovascular Effects

Reduced heart rate (beyond normal athletic bradycardia)
Low blood pressure
Cardiac structural changes
Increased cardiovascular risk

Immune Suppression

Frequent illness
Slow recovery from infections
Increased injury risk
Poor wound healing

Psychological Impact

Depression
Irritability
Anxiety
Impaired concentration
Decreased motivation
Disordered eating behaviors (which worsen the cycle)

Performance Decline

Despite the goal of improving performance:

Decreased endurance
Reduced strength
Impaired coordination
Slower recovery
Increased injury rates
Worse competitive results

Warning Signs

Early Signs (Often Missed)

Feeling cold all the time
Fatigue despite adequate sleep
Frequent minor illnesses
Slow recovery between workouts
Declining performance despite training
Mood changes (irritability, low motivation)
Difficulty concentrating
Food preoccupation or anxiety around eating

Clearer Signs

Women:

Irregular periods (cycles outside 21-35 days)
Missed periods (3+ months without menstruation is red flag)
Very light periods

Men:

Morning erections disappear
Low libido
Difficulty building muscle

Both:

Stress fractures (huge red flag)
Multiple or recurring injuries
Hair loss
Brittle nails
Digestive problems
Exercise feels harder than it should

Serious Signs (Seek Help Immediately)

Fainting or dizziness
Heart palpitations
Severe fatigue
Stress fractures in weight-bearing bones
Signs of eating disorder (restriction, purging, excessive exercise)

Why Athletes Underfuel

Intentional Restriction

Belief that lighter = faster
Making weight for competition
Pressure from coaches or sport culture
Desire for aesthetic ideal
Eating disorder behaviors

Unintentional Underfueling

Not realizing how much training burns
Suppressed appetite from high training load
Busy schedule leading to skipped meals
Poor nutrition knowledge
Gut issues reducing intake

Both pathways lead to the same consequences.

Treatment and Recovery

Step 1: Recognize the Problem

Many athletes resist acknowledging RED-S because:

They don't feel like they're undereating
Menstrual loss has been normalized
They fear weight gain
They don't want to reduce training

But denial prolongs damage.

Step 2: Increase Energy Availability

The foundation of recovery is eating more. This typically means:

Adding 300-600+ calories daily initially
Eating consistently throughout the day
Including adequate carbohydrates
Ensuring sufficient dietary fat
Not restricting food groups

Working with a sports dietitian is highly recommended.

Step 3: Reduce Training If Necessary

Sometimes training volume must decrease temporarily to:

Reduce energy expenditure
Allow body systems to recover
Enable proper fueling (eating more is easier with less training)

This is often the hardest part for athletes.

Step 4: Address Underlying Issues

If disordered eating or eating disorders are present, psychological treatment is essential. RED-S recovery requires addressing the "why" of underfueling.

Step 5: Monitor Recovery

Signs of recovery include:

Return of menstruation (women)
Improved testosterone levels (men)
Better energy and mood
Improved performance
Normalized heart rate and temperature
Fewer illnesses and injuries

Full recovery can take months to years, depending on severity and duration.

Fueling Properly: The Basics

Energy Availability Target

Sports scientists recommend at least 45 kcal/kg of fat-free mass/day for health.

Example: A 130-pound (59kg) athlete with 20% body fat has about 47kg fat-free mass. They need at least 2,100 calories just for health baseline—before accounting for training.

Most athletes need significantly more than they think.

Carbohydrates Are Critical

Carbs fuel training and support hormones. Low-carb approaches are particularly risky for athletes prone to RED-S.

General guidelines:

Light training: 3-5g carbs/kg body weight
Moderate training: 5-7g/kg
High training: 6-10g/kg
Extreme training: 8-12g/kg

Adequate Fat

Dietary fat is essential for hormone production. Athletes should consume at least 1g/kg body weight, often more.

Don't Skip Meals

Eating consistently throughout the day maintains energy availability better than large infrequent meals.

Prevention

For Athletes

Track energy intake periodically to ensure adequacy
Never skip meals around training
Monitor for warning signs (period changes, fatigue, illness)
Prioritize fueling for health over appearance
Work with sports nutrition professionals
Question any advice to lose weight for performance

For Coaches and Parents

Never comment on athletes' weight or body composition
Focus on performance, not appearance
Ensure adequate fueling is part of training programs
Recognize warning signs and address them early
Create culture where eating is supported, not restricted
Refer to medical professionals when concerned

The Bottom Line

Underfueling doesn't make you a better athlete—it breaks your body down and ultimately destroys performance.

The leanest athlete isn't the healthiest or fastest. The best-fueled athlete is.

If you recognize signs of RED-S in yourself, take it seriously. The consequences—stress fractures, hormonal dysfunction, bone loss, cardiovascular damage—can be permanent if left untreated.

Your body needs fuel. Give it what it needs, and it will perform. Starve it, and it will shut down.

Eat to compete. Eat to recover. Eat to be healthy long after your competitive years end. No performance goal is worth sacrificing your long-term health.