He's attacking the person based on his opinion on a completely unrelated subject. He did not attack his opinion regarding overweight people at all. I didn't read much but it doesn't even appear to be that absurd of an opinion and is backed up with knowledge and experience. Just some people don't like it.

It's literally the same concept of coming on here and saying "Aren't you the same person who says he likes the Chevy Volt?!" It has nothing to do with the subject at hand, it changes the subject entirely (red herring) and attacks the person.