Is it really true that the longer you cook vegetables, the less nutritious they are? I have a friend who is a real health nut. She barely uses any seasonings, oil, etc when cooking. She usually steams her food and eats it totally plain. Even salt and pepper are rarely used. Recently she discovered collard and kale greens. I was telling her how an old boyfriend's mother used to prepare collard greens and how delicious they were, and she went off on this tangent about how there would have been no nutrition left in vegetables prepared the way I was telling her, and that they weren;t even worth eating that way, What is the real truth when it comes to cooking vegetables? I grew up in a household where vegetables were cooked to death and were mushy (second generation Irish American here, so that's how they do it). I prefer my vegetables a bit firm these days. But I'd really like to know if and when greens and other vegetables do lose their nutritional value due to cooking.