Although raw food proponents claim that when you cook food you destroy its nutritional value, research shows that sometimes the opposite is true. Several studies show that cooking food actually helps people access the nutrition in it. For example, one carotenoid, lycopene, is hard for the body to absorb from uncooked food. One study showed that people who ate raw diets had low levels of lycopene. Cooking also allows other antioxidants to become more freely available. Carotenoids and antioxidants are essential to brain health.
However, it is true that some vitamins are lost during the cooking process, such as vitamin C and some B vitamins. But overall, cooking improves the bio availability of nutrients. By occasionally eating raw food you can balance the nutrition you’re getting. Steaming and boiling are the healthiest choices, although if roasting is what it takes to get you to eat your veggies, then do it!