Sports nutritionist Wendy Martinson shares her tips on how to eat well to get the best results, whatever your favourite activity or sport. She advises Olympic athletes and England football players on their diet, is consultant sports nutritionist to the British Olympic Association and is a registered dietitian who works with the NHS as a clinical nutrition services manager.

Can I eat more when I am doing lots of exercise?

If you're doing lots of exercise then you will use more energy each day than if you did little or none. So if you don’t want to lose body fat, you need to more food each day.

You should still make sure you have a balanced diet, though. Aim for larger portions of carbohydrate-rich foods such as wholegrain pasta, rice, sweet potato, porridge and breakfast cereals.

Is it better to eat a diet high in starchy carbs or protein when I am training?

Carbohydrate is the fuel that powers your exercise or sports regime. Protein is also needed in moderate amounts, for muscle growth and repair, but the primary form of energy you use when exercising is carbohydrates. Carbohydrates are the most important form of fuel for muscles, and also an essential energy source for the brain and central nervous system, so they play a vital role in sports where precision, quick decision-making skills, dexterity and coordination are required. They are stored as glycogen in the muscle and liver. These stores are small and so a regular intake of carbohydrate is necessary to keep them topped up. Low glycogen stores will result in poor performance, and increase the risk of injury. The proportions of carbohydrate and protein required will vary depending on the sport so it best to seek advice from a qualified professional on your individual requirements.

How should I time my meals and snacks around exercise?

Once you’ve eaten a meal or snack, allow between one and four hours to pass before you start exercising. Your body needs time to digest; the amount of time will depend on the amount of food you ate.

If it's an average meal, eating around two hours before you exercise works well. The meal should be high in carbohydrate, low in fat and low to moderate in protein. Too much protein or fat will slow down the movement of foods from the stomach, and will make you feel uncomfortable.

Food and drink also plays a part in effective recovery from training. Good recovery is crucial to prevent a midweek slump in energy levels, and to aid muscle growth and repair. When you finish training, aim to have a carbohydrate-rich food or drink within 30 minutes.

Do I need to drink when I exercise?

Dehydration – when the water content in your body falls below its normal level – can have a major effect on exercise performance. It is important to start any exercise session well hydrated, by drinking water, squash or diluted fruit juice regularly during the course of the day.

For any exercise lasting over 30 minutes, though, you should take fluid on board as you are doing it. The more you sweat, the more you’ll need to drink.

Water is usually sufficient for low intensity exercise up to 50 minutes. For higher intensity exercise of over 50 minutes, or lower intensity exercise lasting hours, a sports drink would be of benefit. The carbohydrates in a sports drink will help maintain energy levels, and the sodium will help you stay hydrated.

My friend exercises to lose weight, but I exercise to build muscle. Should our diets be different?

Yes. To lose weight, or more specifically body fat, the amount of energy you consume has to be less than the amount of energy you burn. You’ll need a diet and exercise regime that makes this happen.

There are key steps you can take to reduce the energy content in your daily diet. Reduce fat, which is the most concentrated source of energy, and reduce alcohol. Eat fewer sugary foods such as sweets, chocolates, cakes, biscuits and sugary drinks, and eat regular but smaller portions of complex carbohydrate foods such as wholegrain bread, rice and pasta.

Protein foods such as chicken, fish, lean red meat and low-fat dairy foods should be included in moderate amounts. You should eat lots of fruit and vegetables. It's important to control portion sizes, too.

To build muscle, though, you need to combine a programme of resistance training with a diet that includes enough energy to enable your body to make new muscle.

This energy should mainly be in the form of carbohydrate-rich foods, but you’ll also need a little more protein to provide the building blocks of muscle. Large amounts of protein are not required.

A particularly effective approach can be to eat small amounts of protein and carbohydrate before and after the resistance training session. A low-fat milk shake can work well.

Should I take extra supplements when I am playing sport?

There are many different supplements on the market. Some of them have solid research behind them, and others haven't. Athletes have to consider supplements with extreme caution. In the past, some supplements have been found to be contaminated with banned substances.

First, ensure you have a balanced, healthy diet that suits your sport. Consult a registered dietitian or nutritionist with expertise in sports nutrition to assess this and provide advice on particular supplements.