Jaffa Cakes, juice and jellybeans

So, Sven's boys are heading to Japan with crate loads of Jaffa Cakes, breakfast cereals and baked beans. But are these really the foods of champions? Certainly, the sports dietitians who have calculated the players' nutritional needs think so. According to their estimates, each player will run an average of six miles, expend around 600 calories, and sweat out two litres or more of fluid during every match they play. If these losses aren't replaced through a carefully balanced diet, then Becks and his teammates will soon flounder in the heat.

But what can you eat to power you through exercise? Here, with the help of leading sports nutrition experts, we assess the best pre, during and post-exercise foods.

A lack of potassium in the diet can trigger muscle cramps, so eating potassium-rich foods like fruit and vegetables regularly will mean you are well-prepared, advises sports dietitian Louise Beaver of Leeds Metropolitan University.

Although you don't need a lot of extra salt in your diet, cutting sodium out completely might have an adverse effect and could trigger cramps too. Adding a pinch of salt to your pre-training squash will also help to ward off cramps.

Jaffa Cakes

Jaffa Cakes' energy-boosting properties make them a favourite snack of top athletes.

"Although they have a layer of chocolate, they are low in fat and most of their 42 calories come in the form of carbohydrate, which is converted to glycogen to fuel the muscles," explains Jane Griffin, consultant dietitian to the British Olympic team.

Breakfast cereals or muffins Not just for breakfast, these. Many athletes munch on cereals throughout the day.

"The beauty of cereals is that they provide protein in the milk served with them which makes the meal more palatable and easier to digest," says Griffin. "The England Squad is taking Weetabix and Shredded Wheat with them because of their low sugar content. Cereals are the perfect all-round meal and can be eaten up to two hours before exercise for a sustaining boost."

Toast and muffins are good preworkout foods too. "The rule is to eat something you know will settle well when you start to work out," says Griffin. "You should have tested breakfast foods during training so that you know what works for you. Don't try anything new."

Like the England cricket team, who usually have pocketfuls of jelly beans to top up their glycogen stores when they are fielding, our footballers will almost certainly have a stash of fat-free sweets on hand. "Jellybeans, jelly babies and wine gums are pure carbohydrate, so are great for an instant lift," says Griffin. "Plain popcorn is great too. Munching on these between meals and even during exercise will make sure your body's energy levels don't drop too drastically."

Isotonic drinks

You can easily lose a litre of fluid an hour through sweat when you exercise, more when it is hot. If these losses aren't replaced, performance will plummet. "Each litre of water lost is equivalent to one kilo of body weight," says Professor Ron

Bananas

Maughan of the University of Aberdeen Medical School and an adviser to Britain's sports teams. "If an athlete doesn't drink enough water and their body mass falls too low, it can lead to serious overheating problems."

Players who lose just 3 per cent of body weight in a match (that's about 4lb in weight), will find their performance suffers. Lose 5 per cent and endurance capacity plummets by almost a third. Since Lucozade Sport is the official drink of the Football Association, the squad will be used to drinking that during exercise. Like other isotonic drinks it is formulated to provide carbohydrates, at the same concentration as the body's own fluids, and helps boost endurance in exercise lasting 90 minutes or longer, as well as warding off dehydration. But you can make your own, says Louise Beaver. Simply mix together one part water with one part fresh orange juice and a pinch of salt.

Bananas are among the richest sources of potassium, a mineral that is lost in sweat. One banana contains up to ten times more potassium than is found in a single can of many popular sports drinks. But their big advantage, says Louise Beaver, is that ripe bananas are an easily digestible, convenient source of carbohydrate. "They are better than most energy bars because they are virtually fat-free," she says. "A lot of cyclists and distance runners eat them when they are on the move. "

"These are an excellent post-exercise refueller because they are full of energy and vitamins but are low in fat," says Griffin. "International rugby players and Olympic athletes absolutely love them. Best not to take them before exercise as they have a slight laxative effect which could give you the runners' trots."

Hypotonic drinks

After exercise, you need to replace the fluid and energy you have used up with a convenient source of carbohydrate. "The best time to eat is about 20 minutes after you have stopped exercising, which is when enzymes that convert carbohydrate into glycogen are at their most efficient," says Louise Beaver.

"The problem is that a lot of people can't stomach food then, so they prefer to drink. Hypertonic drinks contain particles of carbohydrate at a greater density than you find in the body's own fluids. To make your own hypotonic drink, simply dilute freshly squeezed fruit juice with water. A lot of top marathon runners prefer flat cola, which has around seven teaspoons of sugar per can."

Baked beans on toast

Banned for England players at the last World Cup, baked beans are firmly back on the menu this year. And with good reason, says Jane Griffin. "A good sports diet is based on a ratio of about 60 per cent carbohydrate combined with around 30 per cent protein and a little fat," she says. "Beans on toast fits this bill exactly. The downside is that beans can cause flatulence, but the body adjusts if you eat them regularly. Spaghetti or egg on toast are other good choices."