how close are you to this person? if you want to do the thing and convince him, then you need to figure out how to do that.

I'd advise you probably aren't gonna teach an old dog any new tricks tho.

if this is somebody who are "fam" with, then you might want to evaluate ways to get him to think. what sorts of stories/tales can you use to get in his head. "you know, I was surprised to learn that peas have a really high glycemic index.

if this somebody you're joking with, you could just mock his decisions to eat candy instead of meat. "oh, well, I guess you're still on that suicide plan. you'll have to save a seat for me in heaven... oh, I wonder if they have any fat enough for your ass"