I'm not sure why this would come up in a conversation really, or why you couldn't just answer in the obvious ways.
I think you're doing a TMI. He's asking friendly, innocuous questions and you're up-ending them. It doesn't mean he wouldn't respect the way that you eat, I just don't think how you eat is good bar-conversation.
Last time I dated, which is when I was 19 -- so a long time ago -- I didn't have a weird diet. But, I also ate in a very healthy manner, and as such, it was very unusual for 19 yr olds. guys would ask me about my favorite pizza place, and I would answer -- even though I rarely ate pizza. Guys would ask me which beers I liked, except that I didn't like beer, so I would mention a microbrew that was difficult to find. Guys would ask me how I liked my coffee and I've never liked coffee so I would say "in ice cream!" which is really the only way I have coffee flavored anything. LOL
He's just looking for banter, not an in-depth explanation of your diet and nutritional preferences. If you get past the 'banter' stage and into a date, you can then make mention of restrictions or whatever, and you'd probably discover that he "respects" things just fine.