I think I would approach it like this, if you really make the post about paleo, make #paleo your first tag. If you just think it might be of interest to paleo dietary issues, use it as a secondary tag.

If it's not directly food related and/or not specifically paleo, probably don't use the tag. For instance, info about GMO and nightshades (dietary effects) would be taggable because they are certainly food(ish). Roundup and detoxification are not really dietary and might get you flagged. However, if you wrote one on (just making something up here) body weight exercises, and slip in a sentence about the many paleo exercise folks out there, then you are back in #paleo territory.

At this point, not many people care. But you are right about flagging, I wrote a science fiction story and accidentally put a space between science and fiction in the tag and someone got all pissy about it.