You’re training harder than ever, logging 70-mile weeks, yet your pace slows inexplicably. Stress fractures appear despite adequate mileage buildup. You haven’t menstruated in six months but dismiss it as “normal for serious runners.” Before attributing these symptoms to overtraining alone, consider this: Relative Energy Deficiency in Sport (RED-S) affects 22-58% of endurance athletes, causing cascading health consequences that extend far beyond missed PRs. Understanding ultra running eating disorders and RED-S isn’t about athletic performance—it’s about preventing permanent physiological damage.
What Is RED-S and How It Differs from “The Female Athlete Triad”
RED-S (Relative Energy Deficiency in Sport) occurs when athletes consume insufficient calories to support both their basic metabolic functions AND their training energy expenditure, creating a chronic energy deficit.
The energy availability equation: Energy Available = (Calories Consumed) – (Exercise Energy Expenditure) ÷ (Fat-Free Mass in kg)
Healthy range: 45+ kcal/kg fat-free mass per day Low energy availability: 30-45 kcal/kg per day RED-S threshold: <30 kcal/kg per day
Beyond the Female Athlete Triad
The older “Female Athlete Triad” model focused on three interconnected issues in female athletes: low energy availability, menstrual dysfunction, and low bone density. RED-S expands this framework to recognize:
- Males are affected (10-25% of male endurance athletes show RED-S symptoms)
- Multiple body systems suffer (metabolic, hormonal, bone health, cardiovascular, GI, immunological, psychological)
- Intentional and unintentional underfueling both cause the syndrome
Why Ultra Runners Face Elevated RED-S Risk
Ultra training creates a perfect storm of factors that promote energy deficiency.
Extreme Caloric Expenditure
A runner logging 70 miles weekly at moderate pace burns an additional 1,200-1,500 calories per day above baseline. Peak training weeks (90-100 miles) can require 4,000-5,000 total daily calories—an amount many runners never approach.
Diet Culture in Endurance Sports
The running community perpetuates dangerous myths:
- “Lighter is faster” (leading to intentional restriction)
- “I can eat whatever I want” (ignoring actual deficits)
- “Real runners don’t need much food” (glorifying undereating)
Social media amplifies these messages, showcasing elite athletes’ bodies without acknowledging professional nutrition support, genetics, or unhealthy practices.
Unintentional Underfueling
Many ultra runners aren’t deliberately restricting—they’re simply failing to match intake to demand due to:
- Suppressed appetite from high training volume
- Time constraints (training leaves little time for meal prep)
- GI distress reducing ability to consume food
- Miscalculating caloric needs
- Prioritizing “clean eating” over adequate eating
The Cascading Health Consequences of RED-S
Chronic energy deficiency triggers a survival response where your body systematically shuts down non-essential functions to preserve critical systems.
Reproductive System Shutdown
In females:
- Menstrual irregularity or complete cessation (amenorrhea)
- Reduced estrogen production
- Fertility impairment (potentially long-lasting)
- Increased miscarriage risk
In males:
- Decreased testosterone levels (30-50% reduction)
- Reduced libido
- Erectile dysfunction
- Decreased sperm quality
Bone Health Deterioration
Low energy availability reduces bone formation and increases bone resorption, creating dangerous fragility:
- Stress fracture risk increases 2-4x
- Premature osteopenia and osteoporosis
- Irreversible bone density loss (especially critical during adolescence and young adulthood)
Critical window: Bone density accumulated during late teens through mid-20s determines lifelong bone health. RED-S during this period causes permanent deficits.
Metabolic Suppression
Your body adapts to chronic deficits by reducing metabolic rate:
- Resting metabolic rate drops 10-20%
- Body temperature regulation impaired
- Constant fatigue and lethargy
- Paradoxical weight gain when eating “normally”
Immune System Compromise
- Frequent upper respiratory infections
- Prolonged illness duration
- Slow wound healing
- Increased injury susceptibility
Cardiovascular Changes
- Abnormally low heart rate (beyond athletic bradycardia)
- Low blood pressure
- Orthostatic hypotension (dizziness upon standing)
- Potential arrhythmias
Psychological Effects
- Depression and anxiety
- Irritability and mood swings
- Obsessive thoughts about food, weight, or training
- Social withdrawal
- Decreased concentration
Recognizing RED-S: Warning Signs and Symptoms
Early identification prevents progression to severe physiological consequences.
Performance Red Flags
- Declining race times despite consistent training
- Inability to complete previously manageable workouts
- Prolonged recovery between efforts (72+ hours soreness)
- Plateau or regression in fitness markers
- Frequent injuries (stress fractures, tendinopathies)
Physical Symptoms
- Menstrual irregularities (periods missed, lighter, or irregular)
- Cold intolerance (always freezing)
- Dizziness, especially upon standing
- Brittle hair or hair loss
- Dry skin
- Constant fatigue unrelieved by rest
- Recurrent illnesses
Behavioral Warning Signs
- Rigid food rules (“clean eating,” excessive restriction)
- Anxiety around meals or specific foods
- Exercise compensation after eating
- Weighing frequently or avoiding scales entirely
- Training through injury or illness
- Social isolation to maintain training/eating patterns
Lab and Medical Markers
- Low estrogen (females) or testosterone (males)
- Low bone mineral density (DEXA scan)
- Abnormal thyroid function (low T3)
- Iron deficiency or anemia
- Vitamin D deficiency
The Spectrum: Disordered Eating vs. Eating Disorders
Understanding the continuum helps identify when professional intervention becomes essential.
Disordered Eating (Common in Ultra Runners)
Problematic eating patterns that don’t meet clinical eating disorder criteria:
- Chronic restrained eating
- Fasting or severe restriction around races (“making weight”)
- Compensatory exercise after eating
- Anxiety about food choices
- Rigid meal timing or food rules
Prevalence: 40-60% of endurance athletes display some disordered eating behaviors
Clinical Eating Disorders (Require Professional Treatment)
Anorexia Nervosa:
- Restriction leading to significantly low body weight
- Intense fear of weight gain
- Distorted body image
Bulimia Nervosa:
- Binge eating followed by compensatory behaviors
- Purging (vomiting, laxatives)
- Excessive exercise to “undo” eating
Binge Eating Disorder:
- Recurrent binge eating episodes
- Lack of compensatory behaviors
- Significant distress
Other Specified Feeding or Eating Disorder (OSFED):
- Doesn’t meet full criteria for above but still serious (e.g., atypical anorexia with normal BMI but significant restriction and symptoms)
Critical distinction: All eating disorders require professional treatment from specialized providers (therapists, dietitians, physicians). Self-management is inadequate and potentially dangerous.
Recovery and Treatment Approaches
Addressing RED-S requires multidisciplinary intervention—you cannot outrun or willpower your way through recovery.
The Treatment Team
Sports medicine physician: Diagnoses RED-S, monitors labs, manages medical complications
Sports dietitian: Creates nutrition rehabilitation plan, challenges food fears, educates on energy needs
Mental health professional: Addresses psychological components, treats co-occurring eating disorders, provides coping strategies
Athletic trainer/coach: Modifies training volume, supports reduced exercise during recovery
The Recovery Process
Phase 1: Increase energy availability
- Reduce training volume by 20-50%
- Increase caloric intake to achieve positive energy balance
- Target: Achieve 45+ kcal/kg fat-free mass energy availability
Phase 2: Restore physiological function
- Monitor for return of menstruation (females) or testosterone normalization (males)
- Track bone density improvements
- Assess metabolic rate recovery
- Timeframe: 6-12+ months for full recovery
Phase 3: Gradual training resumption
- Progressive mileage increase only after biomarkers normalize
- Maintain adequate energy availability despite increased expenditure
- Ongoing monitoring for relapse signs
Reality check: Recovery requires reducing or stopping training temporarily. Continuing high-volume training while underfueled perpetuates the problem and delays recovery.
Prevention Strategies for Athletes and Coaches
For Athletes
Track energy balance periodically: Use apps to ensure intake matches expenditure during heavy training blocks
Prioritize performance over appearance: Focus on what your body does, not how it looks
Challenge diet culture messages: Question “lighter is faster” rhetoric—optimal performance requires adequate fueling
Seek help early: Don’t wait for severe symptoms before consulting professionals
For Coaches
Monitor warning signs: Track performance changes, injury patterns, mood shifts
Avoid weight-focused feedback: Never suggest athletes lose weight or make comments about body composition
Educate on energy needs: Help athletes understand caloric requirements for their training volume
Create safe environment: Foster team culture where fueling adequately is normalized and celebrated
Key Takeaways
- RED-S affects 22-58% of endurance athletes when energy intake fails to support basic metabolism plus training expenditure (<30 kcal/kg fat-free mass daily)
- Chronic energy deficiency causes reproductive shutdown, bone deterioration, metabolic suppression, immune compromise, and cardiovascular changes beyond simple performance decline
- Warning signs include menstrual irregularities, declining performance, frequent injuries, constant fatigue, cold intolerance, and obsessive food/exercise thoughts
- Recovery requires multidisciplinary treatment team (physician, dietitian, therapist) and temporary training reduction to restore positive energy balance for 6-12+ months
- Prevention focuses on tracking energy availability during peak training, challenging “lighter is faster” myths, and seeking professional help at first warning signs
When “Healthy” Becomes Harmful
Ultra running attracts disciplined individuals who excel at pushing limits—qualities that become dangerous when applied to underfueling. The same dedication that drives you through 100-mile weeks can blind you to physiological warning signs until damage becomes severe or permanent.
If you recognize RED-S symptoms in yourself, seeking help isn’t weakness—it’s the same strategic thinking you apply to training. You wouldn’t run through a stress fracture; don’t push through energy deficiency. Contact a sports medicine physician this week, reduce training volume, and prioritize recovery over race goals. Your future athletic career and long-term health depend on actions you take today, not the finish line you chase tomorrow.
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