much greater than that of carbohydrates and only slightly
less than that of the hydrocarbon oils used as fuel (48 kJ g−1). Fats are commonly used
as an energy store, to be used only when the more readily accessible carbohydrates
have fallen into short supply. In Arctic species, the stored fat also acts as a layer of
insulation; in desert species (such as the camel), the fat is also a source of water, one of
its oxidation products.