FEMALE ATHLETE HEALTH • FUELLING • BONE

Female Athletes, Low Energy Availability & Bone Health: Why Eating Enough Is Part of Injury Prevention

Understanding RED-S, menstrual health, stress fractures, recovery and the biology of under-fuelling

A female athlete can train hard, eat nutritious foods, look lean, sit within a conventional BMI range and still be under-fuelled. The missing question is not simply whether her food looks “healthy”. It is whether enough energy remains after training to support bone remodelling, reproductive physiology, immune function, muscle repair, growth where relevant and everyday life. Eating enough is not separate from performance. It is part of the body’s capacity to adapt.

 

1. When “Healthy, Lean and Fit” Can Hide Under-Fuelling

Athlete nutrition has two dimensions: quality and adequacy. Oats, yoghurt, salads, chicken, vegetables, fruit and smoothies can form a nutritious pattern. Yet if portion size, meal frequency or carbohydrate intake does not rise as training load rises, the total may still be inadequate.

Low energy availability can be intentional. Weight-sensitive sports, endurance culture and appearance pressure can encourage the belief that lighter is always faster. It can also be accidental: weekly running rises from 20 kilometres to 50, a second training session is added, work becomes more active, or appetite falls—yet eating remains unchanged.

One missed snack does not create RED-S. Energy intake and expenditure naturally vary. Concern grows when the mismatch is large, repeated or prolonged enough to disrupt normal physiology. Athletes may initially feel fine or even perform better after weight loss, which can hide the cost until recovery, hormones, bone or performance begins to change.

 

This early warning deserves its own foundation; read Why Female Athletes Need to Think About Bone Health Earlier.

2. Low Energy Availability, the Triad and RED-S

Energy availability describes the energy remaining for normal physiological functions after subtracting the energetic cost of exercise from dietary energy intake. In research it can be expressed relative to fat-free mass, but measuring it accurately in the real world is difficult. Food records, exercise estimates and body-composition measures all contain error. Clinical assessment therefore considers patterns, symptoms, risk factors and objective findings rather than relying on one app calculation.

The Female Athlete Triad connected low energy availability, menstrual dysfunction and impaired bone health. Importantly, each component exists on a continuum: an athlete does not need an eating disorder, complete amenorrhoea and osteoporosis before the model becomes relevant.

RED-S broadened the picture. Problematic low energy availability may affect metabolic, reproductive, musculoskeletal, immune, gastrointestinal, cardiovascular, haematological, psychological and developmental systems, as well as performance. RED-S can affect female and male athletes; this article focuses on women because menstrual physiology and female bone-health research provide important clues.

3. Why “Lighter Is Faster” Eventually Breaks Down

Body mass can influence running economy and power-to-weight ratio, but performance is not produced by a number on a scale. It is produced by muscle, glycogen, mitochondrial energy, cardiovascular capacity, nervous-system coordination, connective tissue and recovery. Weight loss can include fat, water, glycogen and lean tissue; lighter does not automatically mean better.

Protein cannot fully rescue a severe energy deficit, and muscle is not excess weight that a runner merely carries. It creates force, stabilises joints and helps absorb and transmit load. Carbohydrate is also central for many moderate-, high-intensity and prolonged sessions. Chronic restriction can make it harder to train at quality, replenish glycogen and recover.

The better performance sequence is simple: fuel supports training quality; recovery allows adaptation; adaptation produces performance. Today’s personal best should not come at the cost of tomorrow’s skeleton, fertility choices, mobility or physical capacity.

For the wider performance system, read Athletic Performance Nutrition: Recovery, Collagen, Gut Health & Sports Performance.

4. Bone Stress Injuries: When Load Exceeds Capacity

Bone is living tissue. Training creates microscopic strain, osteocytes sense mechanical loading, and remodelling cells repair and strengthen the structure over time. This is how appropriate exercise supports bone. The same loading becomes risky when damage accumulates faster than the skeleton can repair it.

Bone stress injury exists on a continuum from early stress reaction to more advanced injury and stress fracture. It usually develops through repetitive loading rather than one major impact. Running volume, intensity, impact, surface, biomechanics, previous injury and rapid training progression all contribute to load. Bone health, muscle, sleep, nutrition, hormones and recovery contribute to capacity.

 

Heart and lungs can feel ready for more training before bone and tendon have completed slower structural adaptation. Persistent focal bone pain, pain that appears earlier during successive sessions, pain with walking or pain at rest warrants prompt professional assessment. “Running through it” can turn an early problem into a more serious one.

See the cellular process in Bone Remodelling Explained: How Your Skeleton Constantly Renews Itself, and the mechanical signal in Why Exercise Builds Stronger Bones: The Science of Bone Loading.

5. Menstrual Health Is a Vital Sign—But Not the Whole Diagnosis

Persistent low energy availability can alter signalling through the hypothalamic–pituitary–gonadal axis, affecting ovarian function and menstrual cycles. Reduced oestrogen exposure can alter bone remodelling, but energy deficiency may also affect bone through other endocrine and metabolic pathways.

Menstrual change is not always complete loss of periods. Cycle length, frequency and ovulation may change gradually. Conversely, apparently regular periods do not prove optimal energy availability. Hormonal contraception can make the picture harder to interpret because some bleeding patterns do not provide the same information as spontaneous ovulatory cycles. This does not mean contraception causes RED-S or should be stopped; it means other clinical clues become more important.

Missing periods should not be celebrated as evidence of training hard. They have many possible causes, and an athlete needs assessment rather than assumptions. Pregnancy, polycystic ovary syndrome, thyroid conditions, medicines and other factors may also affect cycles.

6. Adolescence and Peak Bone Mass

Teenage athletes have two simultaneous energy demands: training and growth. Adolescence is a major period for accumulating bone mass, developing muscle and establishing reproductive function. Under-fuelling during this window can therefore affect more than one season.

Peak bone mass is the skeletal reserve built through childhood, adolescence and early adulthood. Genetics is influential, but energy availability, calcium, vitamin D, protein, menstrual health and loading all matter. A young athlete may focus on this race or selection season; her skeleton must also support decades of life after sport.

The life-course perspective is explained in Peak Bone Mass Explained: Why Your 20s Matter More Than You Think.

7. Fuel the Injury: Recovery Requires More Than Rest

Rest or load modification may be essential for a bone stress injury, but stopping running does not automatically correct the factors that reduced capacity. Rehabilitation should ask why the injury developed: training progression, biomechanics, previous injury, low energy availability, menstrual change, bone density, medicines, nutrient intake and other medical factors may all contribute.

An injured athlete may be tempted to eat far less because exercise expenditure has fallen. Some adjustment may be appropriate, but aggressive restriction can be counterproductive—especially when under-fuelling preceded the injury. Healing is metabolically active and requires energy, amino acids and micronutrients.

The wider food pattern is covered in Why Strong Bones Need More Than Calcium, while protein’s structural role is explored in Why Protein Matters for Healthy Bones.

8. The Female Athlete Fuelling Framework

Before training

Ask what the session requires. For longer, harder or higher-intensity sessions, carbohydrate-containing food and fluid can provide accessible fuel. Timing and portion size should suit comfort. A banana with yoghurt, toast with nut butter, cereal with milk or a small rice-based meal can all work in the right context.

During training

Longer sessions may require carbohydrate, fluid and electrolytes according to duration, intensity, conditions and the athlete’s plan. This is individual sports nutrition—not a universal threshold copied from social media.

After training

Combine carbohydrate, complete protein, fluid and enough total energy. The “anabolic window” is not a few frantic minutes, but delaying food for hours after demanding training can make recovery harder when another session or an already-low intake follows.

Across the day and week

·    Eat regularly enough to create sufficient opportunities for energy, carbohydrate and protein.

·    Match harder training days with more fuel rather than using exercise to earn the same small meal plan.

·    Keep dietary fat and micronutrient-rich foods in the pattern; do not build an athlete diet from lean protein and vegetables alone.

·    Fuel rest days too. Repair, glycogen restoration and bone remodelling continue when formal training stops.

·    Monitor function—recovery, performance, menstrual health, injury and mood—not only body weight.

For recovery timing, read Protein Timing for Health, Performance & Recovery. Hydration is placed in context in Functional Hydration.

9. A Practical Recovery Plate

A recovery plate is not a rigid diagram. It is a way to make sure the meal does more than provide one nutrient.

One example is a chicken and vegetable noodle bowl: prepare broth, add noodles or rice, chicken or tofu, several vegetables and sesame oil, then season to taste. Bone broth can be the savoury liquid and contribute protein and collagen-derived amino acids, but the complete protein, carbohydrate and total meal energy remain essential.

For complete meal ideas rather than ingredient lists, explore 12 Easy Recipes for Active Bodies: Protein, Collagen & Everyday Joint-Supporting Nutrition.

10. Where Collagen Peptides and Bone Broth Fit

Collagen peptides are being studied for connective-tissue and bone-turnover outcomes, including a recent short pilot trial in premenopausal female distance runners. Changes in biomarkers over four weeks are scientifically interesting, but they do not prove that collagen prevents stress fractures or treats RED-S.

Collagen is also not a complete protein. Its amino-acid profile is rich in glycine, proline and hydroxyproline but does not replace foods supplying a robust balance of essential amino acids. Bone broth can contribute fluid, flavour, protein and collagen-derived amino acids within meals. Neither product can compensate for chronic energy or carbohydrate inadequacy.

 

The targeted science and its limits are explored in Collagen Peptides, Bone Health & Female Athletes: Why Under-Fuelling Can Affect Bone Remodelling Before Menopause. For the different roles of protein foods, read Functional Proteins Explained: Why Whey, Collagen & Bone Broth All Have Different Roles.

11. Recognising a Pattern and Seeking Help

No single symptom diagnoses RED-S. Fatigue, poor recovery, recurrent illness, declining performance, mood change, menstrual disruption and injury can have many causes. The value lies in the pattern and context.

Persistent menstrual changes, recurrent bone stress injuries, focal bone pain, substantial unintentional weight loss, difficulty eating enough, disordered eating concerns or unexplained deterioration in health or performance should be assessed. Depending on the situation, a sports physician or GP, accredited sports dietitian, physiotherapist and psychologist may form part of the team. Return-to-sport decisions should be individual and clinically guided.

Frequently Asked Questions

Can you have RED-S at a normal BMI?

Yes. RED-S is not defined by low body weight. BMI cannot measure energy availability, hormonal function, bone remodelling or recovery.

Can weight remain stable during under-fuelling?

Yes. Stable weight does not prove adequate fuelling. The body can adapt expenditure and physiological processes in response to prolonged scarcity.

Can you have RED-S and regular periods?

Potentially. Effects exist on a continuum, and menstruation is only one clue. Apparently regular cycles do not prove that every system is optimally fuelled.

Does hormonal contraception hide RED-S?

It can make bleeding patterns less useful as a marker of spontaneous ovarian function. It does not cause RED-S and should not be stopped without clinical advice.

Is losing a period from exercise normal?

It should not be dismissed as a normal achievement. Menstrual change has several possible causes and deserves appropriate assessment.

Can low energy availability cause stress fractures?

Bone stress injuries are multifactorial. Low energy availability can reduce bone-remodelling and recovery capacity, making it an important risk factor rather than the sole explanation.

Can fasting contribute to RED-S?

It can if a restricted eating window makes it difficult to meet energy and nutrient needs. Fasting does not automatically cause RED-S, but restriction deserves caution when fuelling is already marginal.

Should athletes eat on rest days?

Yes. Requirements may change, but repair, glycogen restoration and normal physiology continue. A rest day is not a no-food day.

How long does recovery take?

There is no universal timeline. Energy, mood or performance may improve before menstrual and bone recovery. Bone adapts slowly, and severity and duration matter.

Do collagen peptides prevent stress fractures?

Current evidence does not establish stress-fracture prevention. Collagen can be considered targeted nutrition, but it does not replace adequate energy, complete protein, carbohydrate, calcium, vitamin D or appropriate loading.

Continue Exploring

·    Women’s Nutrition Throughout Life: Supporting Health, Energy & Wellbeing at Every Stage

·    Women, Muscle & Metabolism: How to Build Strength, Improve Body Composition & Support Healthy Ageing

·    15 High-Protein, High-Fibre Recipes for Blood Sugar & Metabolic Health

Final Thoughts

The most important lesson from RED-S is that appearance can conceal physiology. A woman can look strong and disciplined while her body is quietly negotiating an energy shortage. Bone, hormones, immunity, muscle and performance do not read the “healthy” label on a meal; they respond to whether enough resources are available for the work being demanded.

The strongest athlete is not the one who can survive on the least food. It is the one who can train, recover, adapt and keep going. Fuelling is not a concession or a failure of discipline. It is part of injury prevention, performance and the long-term physical capacity that sport should help build.

References & Further Reading

·    2023 International Olympic Committee consensus statement on Relative Energy Deficiency in Sport

·    2025 update to the Female Athlete Triad Coalition consensus statement: clinical guidelines

·    Low energy availability and RED-S: systematic review and meta-analysis

·    Effects of collagen peptides on bone-turnover markers in female distance runners: randomised pilot study

This article provides general education and is not a diagnostic or treatment guide. RED-S, menstrual changes, bone stress injuries and disordered eating require individual assessment. Seek prompt medical care for persistent focal bone pain, inability to bear weight, significant menstrual change, recurrent injury or other concerning symptoms.