Nutritionist Glen Cardwell talks about raw versus cooked vegetables in his book Stop Telling Nutrition Fibs.
"Firstly, let's get the dead obvious out of the road. Some vegetables need to be cooked before they become remotely edible. Raw potato, pumpkin, turnip, swedes and legumes, for example, will not be found in the gourmet restaurant. The entire legume group needs to be soaked and cooked before being considered a food.
"It is well established that many vitamins, like vitamin C, are easily destroyed by heat and light, hence the recommendation to quickly cook vegetables in minimal water… to discourage the leaching of nutrients into cooking water, as this is usually thrown out. Mineral losses are generally low during normal cooking.
"Many studies have revealed that beta-carotene and antioxidant phenolic compounds are actually more biologically available from cooked vegetables compared to raw. That is, they become easier to absorb from the small intestine… probably due to cooking breaking down the tough cell walls, releasing more nutrients.
"Researchers have found that cooking tomatoes can double the amount of lycopene that we can access. A study in 2002 showed that cooked sweet corn has a higher antioxidant activity than the same corn before cooking."
The bottom line: Mostly myth
If you like raw vegetables, go for it. Eating a raw carrot is better than eating a bag of chips! But cooking won't destroy most of the goodness in your food. Cooking makes food taste better, it kills food-borne bacteria, and it can make some foods more nutritious, not less. Cook your veges so they keep a bit of 'crunch' for maximum flavour and nutrition.