Ultimately, all cooking degrades the nutrients in our foods. While some foods require cooking to make them palatable, the more we cook, the more the vitamins and other nutrients in foods begin to break down. So, the least amount of heat you need to apply to any food — especially to veggies — is what you should use.
Certain vitamins, vitamin B12 for example, are converted to inactive forms by extreme heat. So, don't nuke the hell out of your leftover lamb chop — you'll get a lot less useful B12.
The best solution to keeping your foods healthy and delicious? Lightly cook (steam, if possible) or microwave for a short period of time. But, the (sometimes) lazy ladies among us can breathe a sigh of relief. Microwaving our food isn't turning it into a nutrition-less mess after all. (i09)