Most Australians could do with more salads and fresh raw foods in their daily diets, but an all-raw food diet is restrictive and unnecessary. There are also some valuable components in some products that are more bioavailable after cooking. The lycopene in tomatoes, for example, is more easily absorbed from cooked tomatoes than from raw. However, the folate in tomatoes is destroyed by cooking. The obvious solution is to eat both raw and cooked tomatoes.
Some cooking methods retain higher levels of nutrients, so let's take a closer look.
Steaming
Steaming preserves around 90% or more of most vitamins, including folate ? the most fragile of the vitamins. There is almost no loss of vitamin E with steaming and the limited research on retention of antioxidants also supports steaming as the top cooking method.
Stir-frying
With a quick stir-fry in a hot pan using a little oil, over 80% of most vitamins are retained ? as long as you stir-fry only to the tender crisp stage. If you stir-fry for so long that the vegetables begin to lose their bright colour, their vitamins will also start disappearing rapidly.
Baking
Baking results only in small losses of most nutrients, but is applicable to vegetables such as potatoes, sweet potatoes, pumpkin, onions, carrots, beetroot, fennel, parsnips and swedes. Green vegetables don't taste so good when baked as they lose texture and colour and this will parallel their losses of vitamin C and the B complex vitamins.
Boiling
It might be the most common method of cooking vegetables, but boiling the worst from a nutritional viewpoint. Nutrients leach into the cooking water and the more water and the longer the cooking period, the greater the losses. Some vitamins can be saved if the water is used in soups or sauces, but in general, losses of at least 50% of the vitamins occur with boiling.
Boiling is suitable when making soups as the vitamin-rich liquid is consumed. However, much of the folate from green vegetables will be destroyed, so it's important to enjoy salads as well as soups.
The take-home message is that an ideal diet contains both cooked and raw foods. When cooking, steaming is the preferred method for vegetables, followed closely by stir-frying or microwaving. For top retention of vitamins and protective phytochemicals, avoid boiling or microwaving in large amounts of water for long periods at high power.
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