[G. Adams]

I'd argue that grains of any kind are not part of our natural diet. Grains must be cooked to be edible, and as cooking itself is not natural, eating grains is not really natural.

The only species to be able to eat grains in their natural state are birds. Mammals do not. Their unnaturalness makes them more difficult to digest. If you want to eat for health, you should be trying to put little stress on the system. If you look at other species that are similar to ours, Chimps and Orangutans, you see that they have a largely fruit and veg diet, supplementing it with meats. The great importance of meat in their diets can be seen in the fact that while they will often share the fruit they find, they will jealously guard the meat they get.

Another thing with grains is that they contain phytic acid, which limits the uptake of minerals and vitamens. Some very healthy peoples had a limited intake of whole grains, but they treated them in a special way to neutralise the acids, and also encourage enzymes development within them to make them more easily digestible.