Weight is lost through the break down of triglycerides in the adipocytes into fatty acid, which are in turn broken down through a complex biochemical pathway, called Fatty Acid Oxidation, to produce acetyl CoA (a common fatty acid like oleic acid, 18 carbons long, could be used to acetylate 9 molecules of Coenzyme A). Acetyl CoA is shunted into the Krebs cycle (TCA cycle) in the mitochondria where it is used to generate energy, releasing carbon dioxide (two molecules of CO[SIZE=-2]2[/SIZE] per molecule of acetyl CoA). So the end product of fat catabolism is CO[SIZE=-2]2 [/SIZE], which is exhaled from the lungs during exercise.