The folk wisdom of "eat a bit of everything" seems to go well with humans being omnivores and with not overdosing on any particular harmful ingredient. That was before pollution and allergies were rampant, of course.
This would seem to require that most of the 'wisdom' being embedded in the 'everything' in question.
Good point, foods that have been historically clearly identified as toxic would have already moved into the non-food category. So this advice is effectively saying, "look only at your priors and don't consider or collect new data."
If our ancestors took this advice literally they'd have kept eating things that can obviously kill you, like digitalis.
In reality, I think the spirit of the advice is a warning not to under-estimate the importance of your priors: don't consider new data in isolation.
Nutrition is a case where we have to try to make the best possible use of the data we have no matter how terrible, because we have to eat something now to sustain us while we plan and conduct more experiments.
I want to apply Bayes theorem to make rational health decisions from relatively weak data. I am generally wondering how one can synthesize historical human experiences with incomplete scientific data, in order to make risk-adverse and healthy decisions about human nutrition given limited research.
Example question/hypothesis: Does gluten cause health problems (ie exhibit chronic toxicity) in non-coeliac humans? Is there enough evidence to suggest that avoiding gluten might be a prudent risk-adverse decision for non-coeliacs?
We have some (mostly in vitro) scientific data suggesting that gluten may cause health problems in non-coeliac humans (such as these articles http://evolvify.com/the-case-against-gluten-medical-journal-references/). Let's say for the sake of arguing, that I can somehow convert these studies into a non-unity likelihood ratio for gluten toxicity in humans (although suggestions are welcome here too).
However, we also have prior information that a population of humans has been consuming gluten containing foods for at least 10,000 years, without any blatantly obvious toxic effects. Is there some way to convert this observation (and observations like this) into a prior probability distribution?