I don't want to seem like I'm diagnosing him. I hope that it is all an act and he is taking care of himself. But can't help to worry a bit when he says it.
I don't think it's an act. We can be pretty confident Dan has prediabetes, eats ridiculous amounts of unhealthy stuff sometimes, and should probably be doing a better job watching out for his health.
The thing that's relevant here isn't Dan's shtick, which people invoke totally arbitrarily to explain some of his more unusual antics, but the fact that we don't actually have a particularly good view of his life. We don't know his fitness regimen, how representative of his overall lifestyle these "I've eaten 100-1,000 starbursts in the past week" stories are, how often he checks in with his doctor, and other things along these lines.
With everything he's told us, I think it's right to be a little worried about him. It's just worth remembering that we're missing a good amount of context.