Carbohydrates are a common source of energy in living organisms; however, no carbohydrate is an essential nutrient in humans.Humans are able to obtain most of their energy requirement from protein and fats, though the potential for some negative health effects of extreme carbohydrate restriction remains, as the issue has not been studied extensively so far. However, in the case of dietary fiber – indigestible carbohydrates which are not a source of energy – inadequate intake can lead to significant increases in mortality.