I basically just tell folks that I appreciate their concern, that it’s a complex issue and new science is coming out all the time, that my health is improving on all levels, and that I’ve done my research. If folks (this is my most common experience) go the whole “everything in moderation, you’re being too extreme” route, I will say to them: “I am a sugar addict. Would you tell an alcoholic to drink alcohol in moderation?” Sometimes re-framing it that way is enough to help someone take a step back and change their perspective a bit.If they are genuinely interested in learning about keto, I offer to send them some links, and if they’re not really interested but are just trying to “prove” me wrong, I kindly but firmly set a boundary: “noted, thanks. To each their own,” and decline to engage with them further on the topic. If they think you’re being defensive, who cares? That’s their problem, not yours.
People will try to debate you from a place of ignorance on keto for a range of reasons: the concept is intuitively unsettling to them based on a lifetime of low-fat indoctrination, they feel defensive about their own unhealthy diets and, consciously or subconsciously, feel the need to defend themselves, they worry that you’re doing something risky/extreme/faddish and believe it’s their duty to “set you straight”, etc. But none of that is yours to worry about–it’s all coming from their own issues, so let it go. And confirmation bias is strong, so if someone doesn’t want to concede that you might be right, you can send them thousands of pages of peer-reviewed hard science and it won’t do a thing to sway them. Don’t waste your energy. If folks see you getting healthier and staying that way, and they know you’re eating keto, they have all the information they need should they decide to open their minds to it, and that’s all you can really do for them until/unless their minds do eventually open.
For those who are genuinely interested/curious, I find this video to be a fantastic keto 101 for the average layperson with a short-ish attention span and a lack of inclination to read up on complex science. She presents keto as one good diet of many that “may or may not be right for you”, which I think makes it more appealing for those folks who are wary of being proselytized to by a hardcore keto “true believer”. And for what it’s worth, this was the video that first piqued my interest in keto and explained it in a way I could easily wrap my head around, knowing literally nothing about it beforehand: https://www.youtube.com/watch?v=kc6jUtHJoz0