One of my diet books had a paragraph that suggested that microwaving food was terrible since it supposedly destroyed the enzymes in food. At first read, this was a bummer for me, since I reheat in the microwave religiously.

Thank goodness for Google. A quick search turned up this page on enzymes and food preparation from the Argonne National Library (US DOE).

There are multiple answers, but they all say pretty much the same thing: any heat kills enzymes, so in this case, microwaving isn’t any different from any other method to heat food. But they also claim that the digestive process destroys enzymes anyways, so it’s pretty much a moot point.