I came across some new terms today while I was reading up on how our bodies store and manage fat. There are two types of fat in our bodies, white fat and brown fat. White fat is important in energy metabolism, heat insulation and mechanical cushioning.Brown fat is found mostly in newborn babies, between the shoulders, and is important for thermogenesis (making heat). Since adult humans have little to no brown fat, we'll concentrate on white fat in this article. See the bottom of this page for more on brown fat. Take a few minutes to read this really well written article by Dr. Craig Freudenrich Ph. D. (How Stuff Works.com) that explains the importance of these fats.

Body Fat Basics

The human body contains two types of fat tissue:
  • White fat is important in energy metabolism, heat insulation and mechanical cushioning.
  • Brown fat is found mostly in newborn babies, between the shoulders, and is important for thermogenesis (making heat). Since adult humans have little to no brown fat, we'll concentrate on white fat in this article. See the bottom of this page for more on brown fat.
Fat tissue is made up of fat cells, which are a unique type of cell. You can think of a fat cell as a tiny plastic bag that holds a drop of fat. White fat cells are large cells that have very little cytoplasm, only 15 percent cell volume, a small nucleus and one large fat droplet that makes up 85 percent of cell volume.

How Fat Enters Your Body When you eat food that contains fat, mostly triglycerides, it goes through your stomach and intestines. In the intestines, the following happens: 

  1. Large fat droplets get mixed with bile salts from the gall bladder in a process calledemulsification. The mixture breaks up the large droplets into several smaller droplets called micelles, increasing the fat's surface area.
  2. The pancreas secretes enzymes called lipases that attack the surface of each micelle and break the fats down into their parts, glycerol and fatty acids.
  3. These parts get absorbed into the cells lining the intestine.
  4. In the intestinal cell, the parts are reassembled into packages of fat molecules (triglycerides) with aprotein coating called chylomicrons. The protein coating makes the fat dissolve more easily in water.
  5. The chylomicrons are released into the lymphatic system -- they do not go directly into thebloodstream because they are too big to pass through the wall of the capillary.
  6. The lymphatic system eventually merges with the veins, at which point the chylomicrons pass into the bloodstream.

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