I want my man to be healthy

So my bf of one year has very unhealthy habits (he doesn't watch what he eats at all) and I've noticed he's gained a lot of weight since he graduated in the spring and I'm so worried that it will continue going downhill. I just want him to be around for as long as possible. Diabetes runs in his family so I'm literally freaking out. How do I tell him that he needs to take better care of himself without sounding like a total bitch?