Now, add to that that everyone who has TB bacteria enter there body does NOT get TB. Agreed? I mean, we know that, same as not everyone exposed to malaria gets it, not everyone exposed to a given plague gets it, etc and etc, just like not everyone gets PTSD. Agreed?
Science, biology asks 'why not?' and with the mapping of DNA, the genome project, as I understand it, more and more science is able to say that it is because G1 and A7 where 'on' for this person and A7 was off for that guy at that moment thus he suffered/was infected/etc and the guy right next to him was not (I'm just throwing this out there to make the point, I don't know which is which and does this or that, I've just been told that DNA sequencing boils down to 'switches' that are off or on and in conjunction with others, various combinations, this or that result WILL happen). Point being that getting PTSD is every bit as much biological as TB, or so goes the argument as I understand it. Thus it's the chemical reaction in your brain because of whatever, that makes you more or less likely or even guaranteed to get or not get this or that affliction.
It's tough using paleo examples because we only lived for 20-25 years, not really long enough to know what that sort of diet would mean at 5 or 50 or 75 years of age. That said, the point is that food is medicine. You're so right that what we eat is not just important but central. I think everything is related and interconnected. Stress has a chemical impact on the body and organs. Over time that, like salt or fat or carbs, bad carbs, good ones, green veggies, everything has what boils down to a chemical input to our bodies including mental illness.
So I agree we ALSO need to look at diet but a great diet may help improve your chances of not getting TB or PTSD because you're generally healthier and more able to resist but we also know otherwise perfectly healthy people DO get PTSD and TB and this or that when an otherwise wreck of a person does not. That gets it back to the chemical reactions going on inside of us and how it impacts our DNA 'switches'.