I've always been taught that the nutritionally correct method is to undercook vegetables: “Cooking destroys nutrients, so less cooked vegetables equals healthier vegetables. Raw is even better.” But this common wisdom may not be true.

As an undergraduate I majored in Food Science. The focus on food processing when I was a student was to preserve ascorbic acid levels. Ascorbic acid, better known as vitamin C, is easily damaged by heat exposure; thus, the less heat exposure, the better. But ascorbic acid may not be the best measure of nutritional quality.

In judging a food's nutritional value there are many factors to consider. Though vitamin C content may decrease with cooking, the total antioxidant potential of the food may increase. Much of our interest in vegetables has been the anticancer effect of the phytochemicals they contain. Cooking may increase the availability of these chemicals rather than decrease it.

A researcher at Cornell University has been looking at these questions and examining the antioxidant potential of various foods. He has determined that ascorbic acid, in many instances, plays only a small role in a food's total antioxidant potential. In fact, although cooking may lower the ascorbic acid content of the food, it may increase the total antioxidant effect of the food by releasing other chemicals.

For example in apples, ascorbic acid provides less than 0.4 percent of the antioxidant potential. Cooking the apples and decreasing vitamin C does not lower the antioxidant potential. Most of the antioxidant capacity comes from other phytochemicals. Tomatoes are another example. Raw tomatoes contain about 0.76 micromol of vitamin C per gram of tomato. Heating them for 30 minutes at 190 degrees Fahrenheit decreased their vitamin C level to 0.54 micromol of vitamin C per gram of tomato, about a 1/3 decrease. But at the same time, heating increased available lycopene from 2.01 mg of trans-lycopene per gram of tomato to 5.32 mg. The total antioxidant capacity of the tomato increased as well.

In other words, applesauce may be better for you than apples, and tomato sauce better than fresh tomatoes. Now this isn't the final story and there may be other factors to consider, but clearly the research is no longer arguing against cooking fruits and vegetables.

This is especially good news for cancer patients during chemotherapy. Chemotherapy often lowers white blood cell numbers leaving patients susceptible to infection. Common wisdom has been for them to avoid raw vegetables and salads because they may be sources of bacteria and other infectious agents. The nutritionally-minded patients find themselves in a dilemma, worrying that cooking their food will lower its anti-cancer effect. The truth is that cooking may actually be better for them.