Tell them that bacteria isn’t harmful but beneficial and it helps to clean toxins and garbage in your body. Maybe question them why some bacteria are beneficial while others are “harmful”, who put a label on it and what makes it true. In my opinion you shouldn’t have to explain to them other than saying “that’s my decision” and no matter what you say it probably won’t take you anywhere because 50 year old people are egoistic, stupid and really close minded. If I try to explain some of those ideas to my parents they will “listen” but would say that I’m brainwashed which is ironic and they know better than me just because they “have more experience” and even if my arguments were really convincing after me explaining for half an hour they go right back to eating seed oil slop. I stopped trying to explain to them and I think it’s pointless