Untrue. It matters to metabolism. Here is my way to explain it to people:
Think of your metabolism like a fire, and food is kindling/fuel for the fire. If you don't feed the fire enough fuel, it will slowly die out, and if you feed it too much, you will put it down. Do not over- or under-eat.
Also, think about the kind of fuel you are feeding to the fire. If you throw a bunch of plastic chairs on a bonfire, yes, they will burn, but they will burn slowly and awfully and you'll get cancer from the fumes. But if you feed a bonfire nice dry chopped logs, it will burn strong and healthy all night long. Garbage in, garbage out.