Orangutans are known to eat more than 400 different kinds of food (Kaplan & Rogers 2000). They are primarily frugivores eating a variety of fruits. While Fruit is a good source of energy it does not provide protein and is not available on a consistent basis. Orangutans therefore must also consume other foods including insects, young leaves, pith, seeds, bark, stems and shoots (Anbel-Simon 2000; Kaplan & Rogers 1994; Nowak 1999; van Schaik 2004).

The irregular pattern of fruiting and flowering in tropical rainforests means that frugivores like orangutans must forage or range over a large area in order to get enough food (Kaplan & Rogers 2000).

When fruit is scarce orangutans turn to vegetables, chewing on the tips of lianas, discarding the chewed up fiber. They also consume a variety of herbs, palm hearts ad the pith of rattans. In even harder times they will resort to bark (van Schaik 2004).

Like humans orangutans have a taste and preference for sweet foods. They will even brave bee stings to steal honey from hives (Kaplan & Rogers 2000).

Meat eating in orangutans is not common but tends to occur during periods of high demand for protein and during food scarcity. Typically it is the result of taking advantage of the moment rather than active hunting (Kaplan & Rogers 2000; Nowak 1999; van Schaik 2004).

Orangutans will consume medicinal plants on occasion when needed. However, little is known about this behavior. They have also been noted to eat soil on occasion, it is assumed this may be a cure or intestinal ailments (Kaplan & Rogers 2000).

Data on the two subspecies of orangutans has shown differences in diet between the two. Borneans eat less fruit overall and eat more vegetables and tree sap, whereas Sumatrans eat more insects (van Schaik 2004).