Digestion
So what then is a healthy human diet based on what apparatus we have?
I think that there must be a major role for meat and fat. Why else do we have this big meat-protein digestive unit called a stomach? And why the concentrated fat emulsifier called a gall-bladder? I suspect that based on such considerations, the typical human should be eating a diet based on meat and fruit. Relatively few people have allergies to meat and fruit, compared to those with allergies or disabilities with respect to gluten and lactose.
Put another way, if you walked around in the wild, without the supposedly civilising benefits of a good oven, what would you eat? Probably grasses and leaves, fungi, fruit and meat. Tubers perhaps. But not the current deluge of baked goods, high in sodium (yes, because baking uses sodium bicarbonate) and other additives designed to make stuff that feels nice to the mouth but is artificial as hell to the gut. You don't find bread growing on trees.
Maybe we should ignore the pithy daft wisdom of the food pyramid which says eat more starch than anything else. Maybe a diet that prolongs life for Mediterranean people or Ainu is one that would kill other people. Maybe the Chinese really are adapted to eat rice.
Most horrifying, humans are obviously evolving towards a bread-based diet. Eventually, the sufferers of coeliac disease and lactose intolerance will perish from the earth and everyone will drink the breast secretions of animals and eat the overcooked remnants of artificially-cultivated grains. I laugh when I see people protesting about 'Frankenfoods'. Your ancestors, dear children, and you yourselves, have made foods a thousand times more artificial than these.
I mean, think about it, we COOK our food. This doesn't happen in nature. It is terribly unnatural. Worse, we sit around chewing the cooked cud that we don't have the ruminant apparatus for digesting. That's just disgusting.