Lol have you tried the most easiest yet mind boggling of them all; when someone asks why don't you drink milk? Answer: 'why DO you?' Or 'whats so bad about chicken?' Answer: 'what's so good about it?' they can't explain why apart from silly things like they enjoy the taste or they need nutrients ect which it always helps to just reply with a cute LITTLE remark like 'clearly you've done your homework on the topic?' (Add slight sarcasism) Which will make them want to find out all about it

because now they feel stupid...this way your not sitting there 'lecturing'

them (funny how they ask a question you answer it yet your 'lecturing' them lol almost like they are intentionally having a slight poke at you by trying to make you feel like you have done something wrong by lecturing them aka pushing ones beliefs)
Also people have recommended a book 'but you kill ants' not sure if it has stuff that will help as people have usually said this book helps when dealing with rude people that just make up silly excuses, not sure if it provides a view on what to say to silly friends and their silly comments (without lecturing) - but have a read anyways I say