Adipose tissue, body fat, or just fat may be a loose animal tissue composed mostly of adipocytes additionally to adipocytes, fat contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells, and a spread of immune cells like fat macrophages. Adipose tissue is derived from preadipocytes. Its main role is to store energy within the sort of lipids, although it also cushions and insulates the body. Far from being hormonally inert, fat has, in recent years, been recognized as a serious endocrine organ, because it produces hormones like leptin, estrogen, resistin, and cytokine (especially TNFα). The two sorts of fat are white fat (WAT), which stores energy, and brown fat (BAT), which generates body heat. The formation of fat appears to be controlled partially by the adipose gene. Adipose tissue – more specifically brown fat – was first identified by Swiss naturalist Conrad Gessner in 1551.