In the newborn, sugars present in human milk and formulas are assimila
ted by both small intestinal digestion and, especially in the case of
lactose, by colonic bacterial fermentation. Colonic fermentation of ca
rbohydrate serves three major functions: conservation of a fraction of
the metabolizable energy of dietary carbohydrate that is not absorbed
in the small intestine, prevention of osmotic diarrhea, and productio
n of short chain fatty acids that stimulate sodium and water absorptio
n, serve as fuel for coloncytes, and stimulate cell replication in col
on and small intestine.