Not a doctor, but I've read a bit more than Wikipedia on the subject. It's pretty rare (maybe bordering on impossible) for someone to have a damaged metabolism. 100 years ago, such a person probably would not live very long. The most likely cause of that, as far as I know, would be some surgery that shortens their intestines - which means the person actually needs more food because they cannot process it as well. All mammals have the same basic metabolic system. Most of the bugs have been fixed by evolution millions of years ago.