I also think there is some confusion over simple vs complex carbohydrates. I doubt if any of the grains were refined and beans are a protein rich carbohydrate i.e. fava beans along with other beans.
Mixing grains and beans also insures the full complement of amino acids.
Also there are tribes in the mountain areas of central and south America who survive primarily on complex carbohydrates and they are fit and slim.
For the record I am not a full-time vegetarian - a couple of meatless days here and there a week. I still love my pork but in small portions along with greens.