Fat cell. Coloured scanning electron micrograph (SEM) of a fat cell (adipocyte, round, centre) in adipose tissue. Surrounding fat cells and strands of supportive connective tissue are also seen. Adipocytes are among the largest cells in the human body, each cell being 100 to 120 microns in diameter. Almost the entire volume of each fat cell consists of a single lipid (fat or oil) droplet. Adipose tissue forms an insulating layer under the skin, storing energy in the form of fat, which is obtained from food.