A good sports dietitian can make a significant impact on an athlete's performance. Needs and goals vary with sports - athletes may want to reduce body fat, improve energy levels, build muscle or keep immune systems healthy; all of this can be assisted with sound nutrition advice.

Carbohydrate loading

Endurance sports, such as long-distance running, cycling and rowing, require athletes to have an ample store of energy to allow them to perform at their peak for extended periods. It is therefore essential to fuel their reserves with large amounts of carbohydrate foods (carb-loading) in the 3-4 days before their event.

Carbohydrates are abundant in starchy foods such as potatoes, rice, noodles, pasta and bread and are converted in the body into glycogen, which is then stored in the muscles and liver. It is these stores that are then called upon during the endurance event.

In order to successfully carb-load, athletes also need to scale down their level of training at the same time as they are increasing their carbohydrate intake to ensure they don't call on these reserves too soon.

Three large low-fat starchy meals and snacks are advised, e.g. cereals and toast for breakfast, sandwiches for lunch and a pasta meal in the evening with snacks of low-fat yoghurt, toasted muffins or bagels and fruit smoothies in between.

Muscle gain

Many people are under the misconception that gaining muscle is all about a very high protein diet complemented by protein shakes and supplements. Sure, ample protein is important in building and repairing new muscle but only to a level of 1.2-2g protein per kilogram of body weight.

To put that in context, a daily diet of 1 cup muesli, 500ml milk, 1 small pot of yoghurt, 2 eggs, 1 wholegrain bagel, a large chicken breast, 1 1/2 cups cooked pasta, 30g peanuts and a matchbox size piece of cheese would provide 140g protein, the absolute maximum that a 70 kg man could use if he was training hard. The body cannot use any more protein than this so it breaks it down and may store it as fat.

Muscle gain requires athletes to eat more calories than the body needs and this also stimulates their muscles to grow in the form of resistance exercise. Therefore, a high carbohydrate intake is fundamental to provide extra calories and the energy to fuel the stimulating exercise.

Eating for recovery

Recovering adequately from a competition or training session is crucial for athletes, especially if they are competing in a series of events over days or weeks as with the Olympics.

During an event, energy stores are run down, muscles may be damaged and fluid is lost in sweat. Recovery nutrition is about tackling these issues as quickly as possible.

The quicker that carbohydrates are consumed after an event, the more effective the recovery.

In general, it is advisable to have a carb-based snack or meal straight after an event (like fruit and yogurt, beans on toast etc). Quick-release carbs (low-fiber or sugared foods like sweet drinks, jelly beans, white bread) may also be digested more quickly and therefore top up levels more efficiently.

Protein-rich foods directly after (or with resistance sports like weight lifting immediately before) exercise sessions are very important as they are digested more effectively at this time - this helps with muscle repair and building. However, high-quality choices such as meat, poultry fish and eggs are used much better by the body if they are taken with some form of carbohydrate.

The amount of fluid lost can be calculated through pre and post-event weigh-ins and the deficit should then be drunk over the following 2-3 hours. Water is a good choice, although carb-rich sports drinks may be useful to help replenish glycogen stores at the same time.

This nutrition-related column is written by Nina Lenton, a qualified dietitian living and working in Beijing. Contact her at nina_lenton@hotmail.com.