CLA is a mixture of conjugated dienoic derivatives of linoleic acid from safflower oil. Conjugated linoleic acid is found mainly in meat and dairy foods; however it can also be found in certain vegetable oils. Its presence in human tissue comes not only from dietary sources, but also from in vivo oxidation of linoleic acid. Although CLA’s activity as a potent metabolic modulator was first recognized in studies of its anticarcinogenic properties in fried hamburger, research of its metabolic activity has now expanded to include its ability to modulate lipid and energy metabolism, particularly control of body fat and muscle, as well as atherosclerosis. Research in several animal models has demonstrated that CLA reduces body fat accumulation. Some studies have shown that the reduction in body fat occurs regardless of whether the diet is high or low in fat. It appears that increased energy expenditure is responsible for the decreased fat accumulation. Researchers have observed an increase in fat oxidation, but not a decrease in fat biosynthesis. Mice fed a high fat diet with 1% CLA exhibited a 50% reduction in weights of adipose depots, but no significant effects on body weight or energy intake. Energy expenditure persistently increased almost 8% through the trial period. This chronic increase in metabolic rate is thought to be responsible for the reduction in body fat stores. Uncoupling protein gene expression in the mice’s brown fat may be partially responsible for this increased metabolic rate. CLA’s anti-obesity effects have also been suggested to involve an inhibition and/or apoptosis of (pre)adipocytes.