Although the colobines are usually portrayed as leafeaters, it is more correct to describe them as specialising in less digestible food of which leaves are a prominent example.
Leaves are the best year-round source of protein in the rain forest.
But leaves are hard to digest because of their high cellulose content and they are often laced with toxins. No other primates can survive on mainly leaves. Colobines have large complex stomachs containing cellulose-digesting bacteria . The bacteria not only helps to break down cellulose, but also deactivates the toxins. Their stomachs have 3-4 compartments and many folds or pockets in the walls.