Sports Nutrition: An Evidence-Based Foundational Guide for Performance

Why is sports nutrition different?

An athlete who trains regularly and intensely has markedly higher energy and nutrient needs than a sedentary person. Training depletes muscle glycogen, causes micro-damage in muscle fibres, drives fluid and electrolyte losses, and temporarily suppresses immune function. Nutrition influences each of these processes directly: under-fuel and your training quality drops, recovery lengthens, and the risk of injury and overtraining rises.

The goal of sports nutrition is not simply "eat more." It is to deliver the right amount of energy, from the right sources, at the right time. When energy balance stays chronically negative — expenditure consistently exceeding intake — an athlete can develop Relative Energy Deficiency in Sport (RED-S), associated with hormonal disruption, declining bone health, impaired performance and menstrual irregularities. That is why the first step is always energy availability.

Carbohydrate: the fuel of performance

Carbohydrate is the primary fuel for moderate- and high-intensity exercise. It is stored as muscle and liver glycogen, but these stores are limited and can be depleted quickly during hard sessions. When glycogen runs low, fatigue rises sharply, pace falls and concentration suffers. Carbohydrate intake should therefore be periodised to match training load.

Evidence-based ranges are roughly:

• Light/technical day (low intensity): 3–5 g/kg/day
• Moderate programme (~1 hr/day): 5–7 g/kg/day
• High-volume endurance (1–3 hr/day): 6–10 g/kg/day
• Very high load (>4–5 hr/day, multi-day racing): 8–12 g/kg/day

In practice, a 70 kg athlete may need 420–700 g of carbohydrate on a hard training day. Source matters too: the backbone of the diet should be nutrient-dense carbohydrates such as whole grains, fruit, vegetables, legumes and dairy, while rapidly digested sugars are best used strategically around training (immediately before, during and after).

Protein: repair and adaptation

Protein is required to repair the muscle proteins damaged by training and to synthesise new tissue. Current guidelines recommend 1.4–2.0 g/kg per day for athletes; the upper end may be preferred in some situations (for example, strength athletes preserving muscle in a calorie deficit). What matters is not only the total but the distribution: spreading protein across the day, with roughly 0.3–0.4 g/kg (about 20–40 g for most adults) at each main meal, stimulates muscle protein synthesis more consistently.

Quality counts as well. Favour sources rich in essential amino acids — especially leucine — such as eggs, dairy, meat, fish and legumes. Vegetarian and vegan athletes can easily meet their needs by combining varied plant sources and nudging their total protein target slightly higher.

Fats: hormones and endurance

Fats are an important energy source during prolonged low-to-moderate intensity exercise and are essential for hormone production, absorption of fat-soluble vitamins and cell health. Fat should provide 20–35% of total energy. Very low-fat diets can impair hormonal health and performance. Emphasise mono- and polyunsaturated fats (olive oil, nuts, avocado, oily fish) and limit saturated and trans fats. Omega-3-rich oily fish is especially valuable for managing inflammation and supporting recovery.

Nutrient timing: before, during, after

When you eat matters as much as what you eat, especially around hard training and competition.

Before training

A carbohydrate-focused, easily digestible meal 1–4 hours before a session tops up glycogen. A common target is 1–4 g/kg of carbohydrate beforehand; the closer to the session, the smaller the portion and the lower the fat/fibre content. On competition mornings, avoid "new" foods and stick to tried-and-tested meals to prevent gastrointestinal problems.

During training

For high-intensity sessions lasting more than 60 minutes, 30–60 g of carbohydrate per hour helps maintain performance. In very long events beyond 2.5 hours, combining different sugars (glucose + fructose) allows intakes up to 90 g/hour. These strategies should be rehearsed in training through "gut training."

After training

The aims of recovery are to replenish glycogen, kick-start repair and restore fluids. Immediately after a hard session (especially if a second session follows the same day), 1.0–1.2 g/kg of carbohydrate per hour with an accompanying 0.3 g/kg of protein is recommended. For athletes with more than 24 hours to recover, the "anabolic window" should not be over-emphasised; total daily intake is what determines the outcome.

Hydration and electrolytes

Losing as little as 2% of body weight in fluid can impair endurance and cognitive performance. A practical strategy is to weigh in before and after training and replace what was lost: aim to regain roughly 1.25–1.5 litres of fluid for every kilogram lost. In long, sweaty sessions, replace not just water but electrolytes — sodium above all; otherwise the risk of hyponatraemia (low blood sodium) rises. Pale straw-coloured urine is generally a good sign of adequate hydration.

Micronutrients: iron, vitamin D, calcium

Micronutrient deficiencies can quietly undermine an athlete's performance. Three deserve particular attention:

• Iron: Critical for oxygen transport. Deficiency is common in menstruating female athletes and endurance athletes, presenting as fatigue and declining performance. Supplement only when a blood test confirms deficiency and under professional supervision.
• Vitamin D: Important for bone health, muscle function and immunity. Levels can be low in athletes with limited sun exposure or who train indoors.
• Calcium: Adequate intake is essential for bone health and managing stress-fracture risk, especially when energy intake is restricted.

The general rule is food first, pills second. A varied, adequate diet meets most micronutrient needs; supplementation should be targeted and justified.

Supplements: what does the evidence say?

The supplement market is vast, but the number of substances with strong evidence for genuinely supporting performance is small. Those with high-quality evidence include:

• Creatine monohydrate: Supports power and muscle mass in short, high-intensity and repeated efforts. Typical use is 3–5 g/day; it is among the most studied and safest ergogenic aids.
• Caffeine: Improves endurance and alertness. An effective dose is usually 3–6 mg/kg about 60 minutes before exercise; consider individual tolerance and effects on sleep.
• Beta-alanine: Can delay fatigue in high-intensity efforts lasting 1–4 minutes.
• Dietary nitrate (beetroot juice): May benefit some endurance contexts.

By contrast, most "fat burners" and miracle-claim products have weak evidence. The risk of contamination and doping in supplements is real; competitive athletes should choose only independently tested products (such as Informed-Sport) and always seek professional approval.

A sample training day (70 kg, moderate-to-high load)

This is only a framework; portions should be personalised to the athlete's weight, sport, goals and that day's training load.

Common nutrition mistakes

• Chronic under-fuelling: Under-eating to stay "light" harms performance and health (RED-S).
• Neglecting the training window: Failing to fuel before and skipping recovery after.
• Insufficient hydration and electrolytes: Drinking only water and forgetting sodium.
• Investing in supplements before the basics: Trusting pills before the kitchen is in order.
• Trying new things on competition day: Using untested meals or products when it matters.

Personalising by sport and goal

There is no "one size fits all" prescription in sports nutrition; the principles stay the same, but the emphasis shifts by sport. Endurance athletes (distance running, cycling, swimming) stand out for their high daily carbohydrate needs; for them, fuelling strategy — topping up glycogen and taking carbohydrate hourly during long sessions — is decisive for performance. For strength and power athletes (weightlifting, throws, short sprints), protein distribution and total energy are more critical to supporting muscle mass and power; evidence-backed aids such as creatine become especially relevant here. Team sports (football, basketball, volleyball) involve both repeated high-intensity efforts and long durations, so they require a "hybrid" approach: pre-match glycogen loading, in-match carbohydrate and fluid, and rapid post-match recovery are planned together.

The goal also shapes the strategy. An athlete seeking to gain muscle emphasises a modest calorie surplus and adequate protein; an athlete aiming to reduce body fat applies a controlled calorie deficit while keeping protein high and protecting training performance. The key principle is this: nutrition should be periodised to the training calendar and the phase of the season. Energy and macronutrient targets differ across the preparation, competition and transition phases.

Female athlete nutrition and energy availability

Several points carry special importance in female athlete nutrition. The most critical is the energy availability we discussed earlier. If the energy remaining for bodily functions after training expenditure stays chronically low, RED-S can develop, affecting not only performance but also hormonal health, bone density and the menstrual cycle. The loss of the menstrual cycle (amenorrhoea) should not be considered normal but treated as a warning sign.

The second critical issue is iron. Owing to menstrual losses, sweat losses and in some cases inadequate intake, iron deficiency and iron-deficiency anaemia are relatively common in female endurance athletes, presenting as fatigue, breathlessness and declining performance. Iron supplementation should only be done when deficiency is confirmed by a blood test (including ferritin) and under professional supervision; unnecessarily high doses of iron can be harmful. Calcium and vitamin D should be consumed in adequate amounts to support bone health and manage stress-fracture risk. The message is clear: while "eating less to stay light" may seem appealing in the short term, it is costly for both health and performance in the long term.

Nutrition for young athletes

Children and adolescents do not just train; they also grow and develop. Their energy and nutrient needs must therefore be met in a way that supports growth. Priorities for young athletes are adequate energy through regular main meals and healthy snacks, calcium and vitamin D for bone development, and sufficient protein to support growth. Performance supplements are generally unnecessary and not recommended in this age group; the foundation is a basic, balanced and varied diet, together with a healthy relationship with food. Parents and coaches should avoid placing pressure on weight or appearance and instead emphasise performance and health. Positive eating habits built early benefit the athlete throughout their entire career.

Gut health and gastrointestinal comfort

Gastrointestinal (GI) problems are common during training and racing, especially in endurance athletes: bloating, cramps, nausea or diarrhoea can seriously impair performance. Several practical strategies reduce these issues. Reducing fibre and fat in pre-competition meals, choosing tried-and-tested familiar foods, and avoiding "new" foods on race morning are fundamental rules. Athletes who will consume large amounts of carbohydrate during long events should "train the gut" by practising this gradually in training beforehand — known as gut training. Adequate but not excessive hydration also matters for GI comfort. Individual tolerances vary greatly, so the strategy should be tested in training, not in competition.

A practical staple shopping list

Good nutrition starts with the right ingredients in the kitchen. A nutrient-dense, versatile and economical staple list might look like this:

• Carbohydrate sources: oats, rice, bulgur, wholegrain bread/pasta, potatoes, fruit
• Protein sources: eggs, chicken, fish, red meat (in moderation), milk, yoghurt, kefir, legumes
• Healthy fats: olive oil, walnuts/almonds, avocado, oily fish
• Vegetables and fruit: seasonal, with a variety of colours (for micronutrients and antioxidants)
• Practical snacks: fruit + yoghurt, nuts, a wholegrain sandwich

This framework can be easily adapted to budget, cultural preferences and individual needs. The key is to make processed, sugar-dense products the exception and to build the backbone of the diet from these nutrient-dense foods.

Nutrition, sleep and immune health

Periods of intense training and competition can temporarily suppress the immune system, increasing susceptibility to upper-respiratory infections in particular. Nutrition directly influences this picture. Inadequate energy and low carbohydrate intake deepen immune suppression during long sessions, so getting enough fuel in heavy periods matters not just for performance but for staying healthy. Adequate protein, a balanced vitamin D status, micronutrients from plenty of vegetables and fruit, and sufficient fluids are foundational supporters of immunity.

A common mistake here is trying to "boost" immunity or recovery with high-dose antioxidant supplements (for example, very high-dose vitamins C and E); the evidence suggests this approach is unnecessary and may even blunt training adaptations. The most effective "immune supplement" is often sleep: regular, sufficient sleep is perhaps the most powerful and most underused tool for hormonal balance, recovery and immunity. When nutrition, hydration, sleep and sensible training load are addressed together, the athlete both performs better and stays healthier across the season.