Concerned about his health, how to talk to him?

I am legitimately concerned about my boyfriend's health. When I met him he weighed 220 pounds, he's 6 foot 6 so it made him a little bit chubby and that never bothered me.

Over the last two and a half years he has gained quite a bit of weight. He now weighs about 280 pounds. He has asthma and he smokes and I often get super worried when he breathes really hard from doing something physical, whether it is going for a jog with me (which is rare), or working on something in the garage.

He always pokes fun at me because I have lost a lot of weight since we started dating. It hurts my feelings when he points out "all the bones" he can see. It makes me nervous to talk to him about his health and how it would be BEST for him to lose some weight. I do not want him to think that I am not attracted to him anymore, because I still am and I still think he is the most handsome man I have ever met. I don't want him to think I'm being superficial.

I love him so much and it makes me sad when he says he probably won't live much longer than 20 more years because he is "fat and out of shape". I honestly don't know how to bring up the issue.

What would be a good way to talk to him about it? If he wants to remain the weight he is that is fine, but I want him to stop telling me that he is going to die because of it. It really scares me. It's not funny to me.
Concerned about his health, how to talk to him?
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