Brown Adipose Tissue or brown fat, I saw a science documentary about this in the early 70's maybe, and it was about the hypothesis that brown fat "burns" glucose to provide body heat in warm blooded animals. It seemed reasonable to me since the brown fat is attached to all the internal organs which are well supplied with blood, heating the blood like a central heating boiler, the blood then circulating around the body like a heating system. The hypothesis was scorned at the time, now it seems to be accepted science. From Wikipedia:
The mitochondria in a eukaryotic cell utilize fuels to produce energy (in the form of ATP). This process involves storing energy as a proton gradient, also known as the proton motive force (PMF), across the mitochondrial inner membrane. This energy is used to synthesize ATP when the protons flow across the membrane (down their concentration gradient) through the ATP synthase enzyme; this is known as chemiosmosis.
In warm-blooded animals, body heat is maintained by signaling the mitochondria to allow protons to run back along the gradient without producing ATP. This can occur since an alternative return route for the protons exists through an uncoupling protein in the inner membrane. This protein, known as uncoupling protein 1 (thermogenin), facilitates the return of the protons after they have been actively pumped out of the mitochondria by the electron transport chain. This alternative route for protons uncouples oxidative phosphorylation and the energy in the PMF is instead released as heat.
To some degree, all cells of endotherms give off heat, especially when body temperature is below a regulatory threshold. However, brown adipose tissue is highly specialized for this non-shivering thermogenesis. First, each cell has a higher number of mitochondria compared to more typical cells. Second, these mitochondria have a higher-than-normal concentration of thermogenin in the inner membrane.
Phew I didn't get much of that, but it seem all are cells are capable of generating heat from glucose by the action of the mitochondria within the cell, however brown fat is particularly well adapted for this and appears to have no other function. We warm blooded creatures, burn a large portion of our daily intake just to keep warm. I believe the efficiency of brown fat varies in people, I've known guys who can eat what they like and their weight remains absolutely constant, but even while they are eating they break sweat, as if the boiler turned up the heat and they sweat it off. Some people at the other end of the spectrum are conservative with energy and store energy rather than waste it as heat.
Will it ever be possible to control the rate of burn in brown fat, obesity, just take a pill, sweat it off, eat what you like. Before that will quacks get on the bandwagon trying sell ways of turning on brown fat.
BROWN FAT CURES OBESITY PANDEMIC