I just read through this thread and picked up on a couple of things.
1. Mendel lived from the 1820s to the 1880s. there is at least one photograph of him[ a real one, not a photo of the famous portrait.] I've seen it at the Brno Monastery.That's not 300 years ago.
2. We can't digest unprocessed grains.
you can try a little experiment: Saliva contains amylase, which breaks down Cooked starch to maltose.
keep a bit of water biscuit in your mouth, tucked inside your cheek. After a few hours, you will taste the sweet maltose. Try again with unprocessed grains and the change won't happen.
the amylase in the small intestine isn't very different from that in the mouth.So digestion of uncooked starch doesn't take place there either.
I have tried to find out, when in history humans started to eat grains and at what point, they found out you have to cook them. If anyone knows, please show me the references.
I suspect, that it all started with sprouting grains, which are more digestible.
I also tried to find what micronutrients I should be deficient in. I've low carbed for 3 years. I can't find the evidence for this either. It's pretty much impossible to be vitamin deficient whilst eating meat. Meat contains more vitamins than anything. This includes citrus fruits. the reason that sailorss developed scurvey was not just that they had no fruit and vegetables, but that they ate mainly starchy "ships biscuits" with very little good meat.