Advice on how to support SO

My boyfriend is unhappy with his body, and has tried to start going to the gym/ eating better to lose weight but has a really hard time motivating himself, so hasn't been able to keep going consistently. I love him no matter what but of course, I do encourage him to be healthier. My question is, what's the best way I can encourage him to go to the gym without nagging or accidentally making him feel bad about himself? What helps you all and your partners?