Re: Why proteins in diet must be digested, and how its carried out in mammal.

Any elementary book on nutrition, or numerous magazine articles 
about diet, nutrition, etc. would answer this question. Basically, the 
process of digestion hydrolyzes proteins into the constituent amino 
acids, which are then absorbed in the small intestine of  all 
mammals. Amino acids are simple diffusible substances, the 
"buiding stones" that animals and man will use to reconstruct its own 
large specific protein molecules, Protein is needed for growth, weight 
maintenance, repairs tissues including replacing blood plasma and 
hemoglobin, heals wounds, resists trauma and infection, and fatty 
degenertation and cirrhosis of the liver are essentially prevented. 
Poor health and even death can occur without proper protein nutrition.