Bake, fry or boil: which is best?

You may pick out healthy food in the shops but the method you choose to cook it could rid it of all its goodness. Alice Hart-Davis asks the experts for their top tips on how to get the most from your food.

Baking: Wrapping fish in foil and baking it is a good way to cook it - as long as the oven isn't too hot. "High temperatures alter the biochemical structure of the essential fats in the fish," warns nutritionist Ian Marber. "Cook fish at a lower temperature, but for longer."

Baking is also a good way to cook potatoes, says Frankie Phillips, nutrition scientist at the British Nutrition Foundation, because people usually eat the skin, which is rich in fibre and helps the cooked potatoes retain their vitamin C content.

Boiling: "Cut vegetables into larger pieces," says nutritionist Alison Loftus, "as it reduces the surface area through which water-soluble vitamins such as B and C can leach out. Boil them for as short a time as possible, and don't keep them hot for hours as prolonged heating destroys folates, which have an important role in preventing heart disease."

Steaming: "The preferred way to cook vegetables," says Marber. "You lose fewer nutrients and retain fibre, which is crucial for clearing excess toxins and cholesterol from the body and for keeping your bowels moving."

Frying: Frying results in fatty food which is high in calories and not a good thing. Then there's the question of what you fry things in.

"When you heat oils to high temperatures, their chemical structure gets deformed," says Loftus. "It used to be thought that olive oil didn't deform in the way that unsaturated fats such as sesame seed oil or sunflower oil did, but it does, which encourages free radical damage in the body and can cause premature ageing."

Perversely, butter or unrefined coconut oil is a better option for frying, even though they are saturated fats which we have been taught to avoid hitherto.

Deep frying: This method adds fat to food, and causes the formation of acrylamide particles, though more research is needed on quite what these do to the body. On the plus side, says Phillips, if the oil is sufficiently hot, thick-cut deep-fried chips will retain a good proportion of their vitamin C, because the cooking method seals the surfaces fast.

Roasting: A simple and effective way to cook meat and vegetables such as peppers, onions and aubergines. But be careful not to burn the food, advises Marber, as it is all too easy for food to end up charred or singed at the edges.

"Anything burnt is carcinogenic," he points out. "Burnt particles of food give rise to free radicals in the body, more than are matched by the amount of antioxidants contained in the vegetables you are eating."

Grilling: "It's a good way to cook many foods because you're not adding fat," says Phillips. "As long as you don't burn the food," adds Marber. "The trouble is, we like to cook things until they are brown, at which point they will be close to charring."

Microwaving: "Don't lose your perspective," says Marber. "In nutrition, everything is a question of balance. Yes, microwaving affects the nutritional content of vegetables, but if you only cook them until they are crisp, they will still retain their fibre content." And, as Phillips points out, if the convenience factor of microwaving means that it encourages people to eat vegetables that they otherwise wouldn't eat, then that is a good thing.

Ian Marber, The Food Doctor (020 7792 6700; www.thefooddoctor.com). Alison Loftus, Hale Clinic (0870 167 6667). British Nutrition Foundation (020 7404 6504; www.nutrition.org.uk).