At the end of the day, nothing I say or do can help him see this. Mormons have a well-known code of health, called the Word of Wisdom.
It seems like you havent had enough time to get to know him, and honestly you wont for a while.
When I was a teen, my first boyfriend was a convert and people would comment on that instead of how nice he was to me. Better to now what you're going into in a relationship with a doctor or would-be-doctor.