How Nutrition Affects Exercise Performance
Exercise performance is directly influenced by the availability of fuel (primarily glycogen — stored carbohydrate in muscles and the liver), hydration status, and the adequacy of overall nutrition across preceding days and weeks. None of these factors can be meaningfully compensated for by a single pre-workout meal, but the immediate pre-exercise period does represent an opportunity to optimise conditions for the session ahead. Understanding what fuels exercise helps clarify why specific nutritional strategies improve performance.
For moderate to high-intensity exercise, carbohydrates are the primary fuel source. The body can store roughly 400–500g of glycogen across the liver and muscles — enough to fuel roughly 60–90 minutes of intense exercise before these stores become significantly depleted. When glycogen runs low, performance declines markedly: pace drops, perceived effort increases, and the ability to sustain high-intensity work reduces. Pre-exercise carbohydrate intake helps ensure that glycogen stores are topped up before starting.
Protein intake around exercise matters primarily for muscle protein synthesis — the process by which muscle is repaired and built in response to training. While the importance of consuming protein immediately after training has been overstated in gym culture (total daily protein intake matters more than exact timing), consuming adequate protein in the hours surrounding training does support better recovery and adaptation compared to consuming all protein at unrelated times of day.
- Carbohydrates are the primary fuel for moderate to high-intensity exercise.
- Glycogen stores support roughly 60–90 minutes of intense exercise when full.
- Protein around training supports muscle repair, but total daily protein matters more than exact timing.
- Hydration status significantly affects both performance and perceived effort.
- Overall diet quality across the week matters more than any single pre-workout meal.
What to Eat Before Exercise
The ideal pre-exercise meal is carbohydrate-rich, moderate in protein, low in fat and fibre, and consumed 1–3 hours before the session. Fat and fibre both slow gastric emptying — the rate at which food leaves the stomach — which can cause discomfort and bloating during exercise. Foods that are gentle on the digestive system while providing fast-available carbohydrate are ideal: toast with peanut butter, oatmeal, banana, rice with a small amount of protein, or a smoothie with fruit and yoghurt all fit this profile.
If the training session is first thing in the morning and eating a full meal is not practical, a small pre-workout snack is beneficial over no food at all. A banana, a small bowl of oats, or a piece of toast provides enough glucose to meaningfully improve performance in sessions lasting more than 45 minutes. Some people perform well in a fasted state for shorter, lower-intensity sessions — individual tolerance varies significantly, and personal experimentation is the most reliable guide.
For sessions lasting longer than 60–90 minutes — particularly endurance exercise like long runs, cycling events, or extended team sport — intra-workout carbohydrate intake becomes relevant. Consuming 30–60g of carbohydrate per hour from simple, easily digested sources (sports drinks, gels, bananas, dried fruit) during the session prevents glycogen depletion and maintains performance in the later stages of exercise. This is not necessary for gym sessions of under an hour, where pre-exercise glycogen levels are typically adequate.
- Eat 1–3 hours before exercise: carbohydrate-rich, low fat and fibre to avoid discomfort.
- Good pre-workout foods: oats, toast, banana, rice, fruit-based smoothies.
- Even a small snack 30–60 minutes before training improves performance versus fasted.
- Sessions over 60–90 minutes may benefit from carbohydrate intake during the session.
- Avoid high-fat, high-fibre meals immediately before exercise — they delay gastric emptying.
What to Eat After Exercise
Post-exercise nutrition serves two main purposes: replenishing glycogen stores that were depleted during training, and providing protein for muscle protein synthesis and repair. Both objectives are best met within two hours of finishing the session, though the urgency of this window has been somewhat overstated — the body continues to synthesise muscle protein for 24–48 hours after a training session, not just in the first 30 minutes. The practical guideline is to eat a balanced meal containing carbohydrate and protein within a few hours of training, without extreme urgency.
A recovery meal containing 20–40g of protein and a moderate amount of carbohydrate covers both objectives effectively. Practical examples: Greek yoghurt with fruit and granola; chicken with rice and vegetables; salmon with sweet potato; a protein smoothie made with milk, fruit, and protein powder; eggs on toast with avocado. The protein source is more important than the carbohydrate source for most people — prioritise getting adequate protein in, and choose carbohydrate sources based on preference and appetite.
For resistance training (weightlifting, strength training), the post-workout protein target is 0.4–0.5g per kilogram of body weight — roughly 28–35g for a 70kg person. For endurance training, carbohydrate replenishment takes on greater importance, and a ratio of approximately 3:1 carbohydrate to protein (e.g., 60g carbohydrate and 20g protein) is commonly recommended for optimal glycogen resynthesis. For recreational exercisers training 3–4 times per week, these precise ratios matter less than simply eating a balanced meal with adequate protein after training.
- Post-workout: eat within 2 hours — carbohydrate to replenish glycogen, protein for repair.
- Aim for 20–40g of protein in the post-workout meal.
- Good recovery meals: Greek yoghurt with fruit, chicken and rice, eggs on toast, protein smoothies.
- For endurance training, carbohydrate replenishment is proportionally more important.
- The 'anabolic window' is longer than gym culture suggests — aim for a meal within 2 hours, not 30 minutes.
Hydration for Exercise Performance
Water is the most important sports nutrition consideration for most recreational exercisers, yet it's frequently the least attended to. Dehydration of just 2% of body weight produces measurable declines in strength, endurance, and cognitive performance. At 3–4% dehydration, performance losses become severe. For a 70kg person, 2% dehydration is 1.4kg of body weight lost through sweat — achievable in less than an hour of moderate exercise in warm conditions.
The practical approach to exercise hydration is straightforward: arrive well-hydrated (urine should be pale yellow, not colourless or dark), drink consistently during the session (approximately 400–800ml per hour for moderate exercise, more in heat), and rehydrate after exercise. The post-exercise rehydration target is approximately 150% of fluid lost — so if you lost 1kg of body weight during exercise (approximately 1 litre of sweat), drink about 1.5 litres over the following hours.
For exercise sessions under 60 minutes in moderate conditions, water is sufficient hydration. Sports drinks containing sodium and carbohydrate become relevant for sessions over 60–90 minutes, in hot conditions, or for heavy sweaters, because they help replace electrolytes lost in sweat and provide additional fuel for sustained performance. For recreational gym sessions and short runs, the expense and calorie content of sports drinks is rarely justified — water is entirely adequate.
- Arrive at training well-hydrated — pale yellow urine is the target.
- Drink 400–800ml of water per hour during moderate exercise.
- Rehydrate post-exercise at approximately 150% of fluid lost (1.5 litres per kg of body weight lost).
- Sports drinks are only necessary for sessions over 60–90 minutes or in hot, humid conditions.
- Thirst is a reliable hydration guide during exercise — drink when thirsty, stop when not.