As pointed out in many sources, grains are not edible to any species of
primate without technological intervention.  After all raw grain is
essentially flour, water and fiber (in French - paper mache) and will cause
a bowel obstruction in any primate if eaten in sufficient quantities.  As
humans have only been eating grains for about 350 generations, our primate
immune systems recognize grain proteins as "foreign" and will therefore
mount a response to them. Auto-immune diseases such as cancer have shown a
mathematical correlation to grain consumption and indeed OSHA lists all
grains as potential work place carcinogens.

Grains also inhibit digestion in primates by absorbing and eliminating many
vitamins necessary to metabolize natural foods.  A good example of this is
Pelegra, a vitamin deficiency disease caused by eating corn - even though
corn contains the very vitamin (nicotenic acid) whose deficiency causes the
disease.

A good account of the effects of grain in ancient times can be found in
Eades' "Protein Power" in the chapter Curse of the Mummies.  This tells of
the thousands of autopsies performed on ancient Egyptians, who in spite of
eating what the "Battle Creek" nutritionalists would consider ideal, had
higher obesity rates, heart disease rates, and probability higher cancer
rates given their short lifespans.

Ray Audette
Author "NeanderThin: A Caveman's Guide to Nutrition"
http://www.sofdesign.com/neander