Why We Get Fat: And what to do about it by Gary Taubes is probably my favorite book to read about this related topic. It won't necessarily convince someone who's not already convinced, but is a good book to get started on when the mindset changes.
I've had people try to give me advice in the past, but I've always thought that I knew better, especially if they were trying to force their views on me. I've had to go on my own health journey to find out what works for me. BJ Fogg's work in behavior change highlights 3 things that will change behavior in the long term: Have an epiphany, change your environment, or take baby steps. It may be that your boyfriend needs some kind of epiphany or experience that makes him realize he needs to change his behavior, but that's not something that can be persuaded by other people.
It's a slow process to change a mindset, and the best you can do is to be patient, supportive, and ready with advice for when he is ready to make a change.