There are many people out there who will tell you that cooking vegetables destroys the nutrients and beneficial enzymes within. This is partially true. It is also true that cooking vegetables makes many of the nutrients and enzymes within more easily absorbed and used by your body. So, which is better? Eating vegetables raw or cooked?
Prehistoric man mastered the art of fire and cooking perhaps as early as 1.5 million years ago. This means that for the majority of human evolution, our ancestors have been eating cooked food. In fact, some believe that the advent of cooking may be one of the most important factors in our success as a species because it greatly increased the nutrition that could be digested out of our food for a lower energy expenditure (this is true for meat and plant matter).
But, some vitamins are very volatile in heat. Vitamin C for example, degrades with heat, dehydration and prolonged storage. Polyphenols are antioxidants known to reduce the risk of cardiovascular disease and cancer which are destroyed by the cooking process. There are some beneficial enzymes that are destroyed by the cooking process; for example: the enzyme myrosinase, whose activity forms sulforaphane, known to prevent cancer, is found in raw broccoli but destroyed in cooking. The allicin in garlic (the compound in garlic responsible for its anti-biotic and anti-microbial effects, also shown to reduce the risk of cancer and cardiovascular disease) is destroyed by heat. There is some very convincing evidence supporting the case for eating raw vegetables.
While some nutrients are lost in cooking, we are compensated by the many other nutrients that are increased during cooking. Heat breaks down the thick walls of a plant’s cells, which makes any nutrients bound to the cell wall or locked inside the cells available to our body for digestion. Typically, anti-oxidants are dramatically increased by cooking. For example, many carotenoids increase in bioavailability when vegetables that contain them are cooked. Lycopene increases when tomatoes are cooked or sun-dried. And some compounds require heat to be formed, such as indole, thought to prevent cancer, which is formed when cruciferous vegetables (like broccoli, cabbage, Brussels sprouts and kale) are cooked.
So I advise mixing it up. Cook some of your vegetables and eat some others raw. Sometimes cook your carrots; sometimes eat them straight out of the bag. Out of sheer convenience, I typically eat raw vegetables at breakfast and lunch and cooked vegetables at supper. Do whatever works for you. Eat your vegetables however they taste the best to you. The most important thing is that you eat them!