At London Bridge Sports Medicine (LBSM), we see athletes of all levels, from professionals to those who enjoy sport as part of a healthy lifestyle. A consistent theme across many consultations is the role nutrition plays in both performance and injury.
While training plans, recovery protocols and injury management are typically prioritised, sports nutrition can often be overlooked. Yet, under-fuelling (not giving the body enough energy to meet the demands of training) is one of the most significant risk factors for stress injuries.
In this article, we explore why nutrition is fundamental to health and performance, the science behind under-fuelling and how it can contribute to stress fractures and other musculoskeletal injuries.
Why Nutrition Matters in Sport
Nutrition is far more than simply ‘healthy eating’. It is the foundation that allows athletes to train, adapt, perform, recover and stay healthy over the long term.
Nutrition plays an essential role in:
- Energy provision – ensuring muscles and tissues can perform under load.
- Tissue repair and recovery – allowing micro-damage from training to repair and rebuild, stronger.
- Bone health – supporting bone density, strength and resilience against stress.
- Hormonal balance – regulating the systems that influence metabolism, menstrual function and mood.
When nutrition is insufficient, the balance shifts; the body is forced to conserve energy, prioritising immediate survival over long-term health.
For athletes, this can manifest as fatigue, reduced performance, recurrent illness, or musculoskeletal injuries such as bone stress fractures.
Understanding Under-Fuelling
Relative Energy Deficiency in Sport (RED-S)
Under-fuelling is often discussed in terms of Relative Energy Deficiency in Sport (RED-S), a condition recognised by the International Olympic Committee. RED-S occurs when energy intake is insufficient to cover the demands of training, recovery and normal physiological function.
The effects of RED-S are widespread. Metabolism slows down, hormones such as oestrogen and testosterone become disrupted and bone repair is impaired.
In women, periods may become irregular or stop altogether, while in both men and women bone health and fertility may be affected. Athletes often notice other consequences too, such as poor recovery after training, frequent illness, sleep disturbances, and changes in mood or concentration.
Common affects include:
- Metabolic rate – slowing down energy use to compensate.
- Menstrual function in women – leading to irregular or absent periods.
- Bone health – reducing bone density and increasing fracture risk.
- Immune function – leaving athletes prone to frequent illness.
- Cardiovascular and psychological health – including low mood, poor concentration, and sleep disturbance.
How Under-Fuelling Happens
Under-fuelling can develop for a variety of reasons. For some athletes, it is unintentional and simply the result of failing to match food intake with a demanding training load.
Others may restrict food in an attempt to change body composition or to achieve a perceived performance advantage.
Busy lifestyles can also contribute, with meals skipped due to work or study commitments. In some cases, misinformation about “healthy eating”, such as avoiding carbohydrates, leads to energy deficits that undermine performance and health.
Common reasons include:
- High training loads without increasing energy intake.
- Restrictive diets – for weight management, aesthetics, or performance beliefs.
- Time pressures – busy schedules leading to missed meals.
- Misinformation – following trends that underplay the role of carbohydrates or
How Under-Fuelling Puts You at Risk for Stress Injuries
Stress injuries, particularly bone stress fractures, are all too common in athletes and active people. They are one of the clearest examples of how under-fuelling can directly harm your body.
They occur when bone is exposed to repetitive loading without sufficient time, or resources to recover. Nutrition is a big part of this equation.
Bone Health and Energy Availability
Bone is a living tissue, constantly being broken down and rebuilt. Old bone breaks down and new bone forms in a continuous cycle, but that process needs plenty of energy and nutrients.
When you don’t fuel properly, several things can go wrong:
- Reduced oestrogen and testosterone – Levels of oestrogen and testosterone, which help protect bone density, decline.
- Lower availability of calcium and vitamin D – Less calcium and vitamin D means fewer building blocks for strong bones.
- Suppressed bone formation – The body conserves energy by cutting back on new bone formation.
All of this leaves your bones weaker and less able to handle the pounding of running, jumping, or other repetitive activities.
Case Example – The Runner with Recurrent Shin Pain
A typical scenario we see at LBSM is a runner who develops persistent shin pain. Training adjustments and physiotherapy may help temporarily, but the pain returns after a few weeks.
On closer consultation, we realise the athlete is under-fuelling and not consuming enough energy and nutrients to support their needs. As a consequence, the tibia cannot remodel effectively and microdamage progresses to a stress fracture.
Without addressing the energy imbalance, rehabilitation alone is unlikely to be successful as the bone remains vulnerable to injury. This is why we ensure our Physiotherapists work closely alongside our Nutritionist to provide a complete rehab service.
How do you know if you are under-fuelling? Sometimes it isn’t easy to know.
Recognising under-fuelling is not always straightforward. Some athletes present with clear red flags, while others may only show subtle signs.
Here are some signs and symptoms to be aware of:
- Persistent fatigue or reduced performance despite training.
- Recurrent injuries or delayed recovery.
- Stress fractures or frequent bone stress reactions.
- Low mood, irritability or difficulty concentrating.
- Disrupted or absent menstrual cycles in women.
- Frequent illness or poor wound healing.
At LBSM, we emphasise a multidisciplinary approach, combining sports doctors, physiotherapists and nutrition specialists to identify and address these issues early.
Preventing Stress Injuries Through Nutrition
Energy Balance
The cornerstone of prevention is ensuring energy balance is achieved; matching dietary intake to training and recovery demands. This doesn’t mean calculating every calorie but rather being mindful of fuelling before, during and after exercise and being mindful of the signs mentioned above.
Macronutrients
- Carbohydrates: The primary energy source for high-intensity sport. Insufficient carbohydrate intake places stress on the body and forces it to break down muscle which impairs recovery.
- Protein: Essential for muscle repair and bone health. Regular protein intake throughout the day is more effective than one large serving.
- Fats: Often overlooked, but crucial for hormone production and joint health. Healthy fats (e.g. olive oil, nuts, oily fish) should be part of every athlete’s diet.
Micronutrients
- Calcium and Vitamin D: For healthy bones and injury resistance.
- Iron: Prevents anaemia and supports endurance performance.
- Magnesium and Zinc: Important for recovery and tissue repair.
Timing of Nutrition
Eating Before Training
Fuelling before training is essential to provide the body with readily available energy and to prevent premature fatigue. The best pre-training meals or snacks depend on how much time you have before exercise.
- 2 – 3 hours before training: Aim for a balanced meal with complex carbohydrates, lean protein and a small amount of healthy fat. Examples include a bowl of porridge with banana and almond butter, a chicken and rice salad, or a wholegrain bagel with smoked salmon and avocado. These provide sustained energy release and help prevent hunger during the session.
- 30 – 60 minutes before training: If time is short, choose a lighter snack that is high in carbohydrates but low in fat and fibre, which can slow digestion. A ripe banana, a slice of toast with honey, a handful of dried fruit, or a low-fat yoghurt with berries are ideal options. These provide a quick energy boost without causing digestive discomfort.
Consuming Protein and Carbohydrates Soon After Exercise
Post-exercise nutrition plays a key role in recovery. During training, muscle fibres sustain micro-damage, and energy stores (glycogen) are depleted. Eating soon afterwards helps the body to repair and replenish.
- The timing: Ideally, aim to eat within 30 – 60 minutes of finishing exercise. This is when the body is most efficient at absorbing and using nutrients.
- What to include: A combination of protein and carbohydrate works best. Protein helps rebuild muscle, while carbohydrates replenish glycogen stores. A good target is around 20 – 25 grams of protein alongside a moderate portion of carbohydrates.
- Examples: A fruit smoothie made with milk or yoghurt and a scoop of protein powder; scrambled eggs on wholegrain toast with some fruit on the side; a tuna and sweetcorn wrap; or cottage cheese with pineapple and oatcakes. For those with less appetite after exercise, a recovery shake or chocolate milk can be an easy first option, followed by a balanced meal later.
Spreading Intake Across the Day
Rather than eating only two or three large meals, athletes benefit from spreading energy intake evenly throughout the day. This approach maintains blood sugar levels, supports consistent energy availability, and promotes ongoing bone turnover and muscle repair.
- Every 3 – 4 hours: Try to eat balanced meals or snacks regularly rather than leaving long gaps without food. For example, breakfast, mid-morning snack, lunch, afternoon snack, dinner, and sometimes a light evening snack if training late.
- Examples of balanced snacks: Greek yoghurt with granola and berries; wholegrain crackers with hummus; peanut butter on toast; a protein bar with a piece of fruit; or a small chicken wrap with salad.
- Examples of meals: Grilled salmon with quinoa and roasted vegetables; a lean beef stir-fry with rice and mixed vegetables; pasta with chicken and tomato sauce, topped with parmesan; or lentil and vegetable curry with wholegrain naan.
By eating at regular intervals, athletes ensure that the body always has the resources it needs to adapt to training, protect bone health, and prevent under-fuelling.
The Role of Healthcare Professionals
At LBSM, we believe managing under-fuelling and stress injuries requires a team approach. Sports doctors identify patterns of injury, conduct investigations such as bone scans, and guide safe return-to-play.
Nutritionists like our in-house specialist, provides tailored advice on fuelling strategies, while physiotherapists address biomechanics and loading patterns.
This collaborative care ensures that underlying issues, not just symptoms, are addressed, reducing the risk of recurrence.
Practical Advice for Athletes
For athletes looking to reduce their risk of under-fuelling and stress injuries, the key messages are simple but important.
- Don’t skip meals, especially around training.
- Prioritise carbohydrate rich foods for energy and protein rich for recovery.
- Include healthy fats daily – such as nuts, avocado or Greek yogurt
- Pay attention to signs such as fatigue, recurrent niggles, or menstrual changes.
- Seek professional advice if you suspect that you are under-fuelling.
Conclusion
Nutrition is not a side note in athletic performance, it is fundamental to performance! Under-fuelling not only limits progress but can actively harm long-term health by increasing the risk of stress injuries and affecting bone, hormonal, and immune function.
At LBSM, our team understands the complex relationship between nutrition, training, and injury. By working together with athletes and recreational exercisers, we aim to prevent under-fuelling, promote resilience, and keep people enjoying the sports they love.
