As with all colors of vegetables, the more they're cooked the more vitamins and minerals are lost. The vegetables tend to break down when exposed to heat. "The longer and hotter you cook them, the more nutrients you are likely to lose. The ideal way to eat vegetables and preserve the biggest amount of nutrients is to eat them raw, but if you are cooking your vegetables, try steaming them either in a steamer or in the microwave. Stir frying also can be a good way to preserve the nutrients. Always use as little water as possible, and avoid boiling vegetables, as the vitamins, minerals and phytochemicals will escape into the water rather than remaining in the vegetables. Also try to keep the vegetables in larger pieces when cooking. The more their surface is exposed to air and/or water, the more likely you will lose those important vitamins and minerals.