Everybody knows that fruit and vegetables contain antioxidants, and are good for you, although we still don't know exactly why. Current research no longer supports the use of antioxidant supplements, but high antioxidant levels in the blood do seem to be associated with a reduced risk of heart disease and some cancers.
However, we're often told that if you cook vegetables you "remove the goodness". This was always code for removing the vitamin C, which does oxidise quickly and is sensitive to heat. But vitamin C is not something we tend to be short of these days, because of all the juice we drink, and how much fruit and veg is available all year round. In fact, plenty of other vitamins are not affected by heat at all, while some, such as beta-carotene, are actually absorbed better because of it.
Beta-carotene is a form of vitamin A, which is valuable for immune function, healthy skin and healthy eyes. It is found in the cell wall of carrots, among other things, which means that if you eat raw carrot you would only be able to absorb a certain amount because your gut cannot break down all the cells. The rest will simply pass right through your digestive tract. When you cook carrots, however, you are weakening some of those cell walls and making the beta-carotene more available, so a greater percentage is absorbed. This is something we can measurably demonstrate in blood levels.
There are antioxidant compounds too, which are also absorbed better from cooked foods. Lycopene, for instance, which is a pigment in tomatoes. Or a group of chemicals called polyphenols. These are not classed as nutrients, meaning that there isn't a deficiency state, but they are associated with healthy effects, and all of them benefit from heat treatment.
The bottom line is: eat a lot of fruit and vegetables, but eat them however you like. Salad, soup, casseroles, boiled, frozen, tinned, stir-fried, whatever. And by all means add garlic, olive oil, cheese sauce or anything else that will help you to eat more of them. Until you're deep-frying peas in batter, I think the balance will always be in your favour.
Ursula Arens is a registered dietician
