text: Large molecules are difficult for the body to absorb into the bloodstream.  By digesting the large molecules into smaller ones, they can be absorbed much more quickly and efficiently.  This lets us get more nutrients out of the food we eat.\n\nAlso, in the case of proteins, the way that amino acids are arranged in proteins doesn't match the arrangement that our body needs for certain things.  The protein is broken down into the amino acids to be absorbed, and then those amino acids can be used to build up proteins that meet the exact specifications that your body needs them to have.