Recognizing factors controlling the balance between food intake and energy expenditure is important in understanding the physiology of obesity. Energy metabolism works through a series of coupled reactions. This means that energy released by breaking down fats, carbohydrates and proteins are captured in other reactions such as making ATP (a high energy chemical) or storing fats and carbohydrates. Uncoupling occurs when the energy from food breakdown is released as heat instead of capturing it as ATP.
The human body contains small amounts of brown fat and uncoupling proteins that convert energy directly into heat. Polish researchers from the Institute of Animal Reproduction and Food Research at the Polish Academy of Sciences in Warsaw in a study on rats found that bile acids produced in the liver as part of digestion triggered uncoupling proteins to increase energy expenditure. This study shows another mechanism the body uses to control bodyweight.