According to the law of conservation of mass, matter is neither created nor destroyed, but it may alter its form through chemical reaction. Essentially, that tells us that while we lose mass in our bodies by burning up fat, it does not just disappear. It simply changes form, like water and steam.
When we eat, the glucose and other sugars harnessed from carbohydrates are the first fuel sources. The liver stores the glucose in the form of glycogen and releases it into the bloodstream as necessary to keep our body trucking along. Think of your bloodstream as an interconnected conveyor belt that takes necessary nutrients to the body parts that need them. Once that glucose runs out, fat takes over. Harnessing energy by burning fat is referred to as ketosis.
Hormones regulating our blood sugar levels activate an enzyme in the blood vessels of fat tissue called lipase. Lipase ignites fat cells to release macromolecules called triglycerides, which are what make fat cells fat. Triglycerides are made of glycerol and three fatty acid chains. When they receive the signal from lipase to exit the fat cells, the triglycerides break up into their respective components and enter the bloodstream for use. The liver snatches up the glycerol to break it down for energy, and some of the fatty acids move to the muscles that can farm them for energy as well.
This action of breaking down triglycerides into usable energy is called lipolysis. Once inside the mitochondria, or power source, or muscle or liver cells, the components of the glycerol and fatty acids are shuffled and reshuffled to harness their energy potential, producing heat, water, carbon dioxide and adenosine triphosphate (ATP). ATP hauls potential energy in its molecular bonds for use when we exercise like cellular carb loading. The water exits our bodies as sweat and urine, and we exhale the carbon dioxide.
Now that the body has relieved fat cells of some glycerol and fatty acids, the cells get smaller. But if the fat tissue shrinks, what happens to our skin?