Such granules have also been seen in preparations of insect fat bodies. Here we note that the fat body is not, as the name suggests, simply a fat storage depot. Rather, it is a complex metabolic center more comparable to the vertebrate liver. Most glycogen is stored in the fat body and to a lesser extent is found in flight muscle cells. This is made of a glycerol backbone, which is a 3-carbon unit.
Most lipid is stored in the fat body, although small amounts are found in other cells.
Some insects oxidize the amino acid proline, sometimes expressed in the correct nomenclature as an imino acid. Insect hemolymph is quite high in amino acid content - much higher than in mammalian blood. The hemolymph is the major storage site of proline. Proline is unique among the energy substrates because its storage, transport and metabolic forms are all the same. Given that we have some idea of the major metabolic fuels and their storage sites and forms, we can go on with the observation that, by and large, the fat body is the major site of energy storage.