Not as attracted to my boyfriend? Ugh

So my boyfriend and I have been together for a year and a half now. We have always been head over heels for each other, and had a really good sex life. Within the last few months, he has gotten a big beer belly, and he's let himself go health wise. He doesn't brush his teeth before sex, and sometimes he smells down there. I'm really worried about him, and I know the reason for this is partially him feeling down, and partially him feeling comfortable with me. Its hard sometimes to feel really amped about sex when he is smelly down there... I have no idea what to say or do, or how to encourage him to change his lifestyle to be healthier. I love him very much and I don't want to complicate things but it makes me a little sad that I'm not as into sex as I used to be. How can I encourage him to be his best self again?