My 100% raw food vegan/hygiene friend asks this question of the Paleo list:

1. Given that glucose is the fuel for the energy production of the
trillions of cells in the body, why does the paleolithic diet, limit
carbohydrate intake to less than the protein and fat intake in the diet?
It is a fact that the body does not store excess protein, so if you have a
high protein intake, one stresses the liver and kidneys in metabolising and
eliminating the excess protein/waste products from protein metabolism.  The
body can store excess fat in the fat cells throughout the body and in the
lining of blood vessels as fatty plaques. The body is less efficient
however in converting fat to glucose for energy production.  Why force your
body to engage in an energy expensive process of converting fat into
glucose when one can provide the body with simple sugars by eating raw
fruits and succulent vegetables?  The fructose in fruits hardly needs any
digestion and thus is a readily available fuel source for energy
production.