How and When Do We Remove Fat from Our Fat Cells?

The fat stored in fat cells is available to us when food energy is not being absorbed (fasting) and when we exercise. Just as the hormone insulin promoted the storage of fat when energy was coming into our body, the process of mobilizing fat from fat cells is promoted by the hormones released into our blood when we are fasting and/or exercising (Figure 5.8). These hormones are glucagon, epinephrine, and cortisol, and all promote the release of fat from fat stores.

In order for fat to be released from fat cells, fat is first broken down to fatty acids and glycerol, which then enter our blood and circulate. However, because of their general water insolubility, the fatty acids will hitch a ride aboard a protein in the blood called albumin. On the contrary, glycerol is fairly water soluble and can dissolve into blood. In fact, researchers will measure the level of glycerol in the blood to estimate how much fat is being broken down.

Body fat is broken down to serve as energy in-between meals and during exercise.

Circulating fatty acids are removed by cells, especially skeletal muscle and our heart, liver, and other organs and then used by those tissues primarily for energy. However, keep in mind that cells of the brain and red blood cells (RBC) cannot use fatty acids for energy and will continue to use glucose. Conveniently the glycerol released from fat tissue can be used to make glucose in the liver and released into circulation to help maintain a desirable level of circulating glucose during prolonged exercise and fasting.