Fat is a great way to store energy.  The problem is that most of us don’t need to store so much.  We store energy as glycogen (K) and store enough of it to be in very good shape, energy speaking.


When all the energy needs are met and the glycogen stores have been filled, the excess glucose is stored as fat.  That means the carbohydrate rich bagel you ate for breakfast has the potential (a very great potential) of being stored as fat.  It isn’t the full fat cream cheese smear you put on your breakfast that is making you fat, it is the fat free carbohydrate sponge that is putting the poundage in your thighs.

Just like glycogen, triglycerides are packages, folded up all nice and neat, so that a high level of energy can be stored.  Because triglycerides are more compact, they are the preferred storage over glycogen and therefore will be burned after the glycogen is gone.  Storage of energy as fat triglycerides  is also unlimited- you can just keep adding to the fat.

Sometimes the terminology gets a little confusing here so I’ll do a quick list of terms:

  • Fatty acids- a free form of fat which circulates in the bloodstream as fuel.
  • Triglycerides-are a stored form of fat locked in fat cells.
  • Adipose- connective tissue in the body used to store energy in the form of fat.
  • Adipocyte- cells that make up the adipose tissue.

The excess glucose is moved back to the liver and this left over glucose is taken up by the hepatocytes for synthesis of fatty acids.  Fatty acids are small enough to move through the cell walls without special transport and thus flow freely in and out.  When the fatty acids are made, they are exported to provide free fatty acids for use in other tissues.  The other tissues will use them along with glycerol to synthesize triglycerides.

Triglycerides are a much larger molecule and therefore are unable to move through the cell walls.  They consist of three fatty acids with a backbone of glycerol.  Once the triglyceride is made, it is unable to move back out of the fat cell without being broken down first.   So essentially they are built up to be stored, then broken down to be used, and built back up to be stored again if not used.  This conversion back and forth is driven by the presence of insulin, glucose, and glycerol-3-phosphate (also called alpha glycerol phosphate at times).

An important player in this whole process is glycerol-3-phosphate.   In its presence, any fatty acids in the cell are converted in to triglycerides.  It is produces when glucose is burned to produce ATP in glycolysis.  So for fat to be stored, glycerol-3-phosphate must be present and for glycerol-3-phosphate to be present, insulin must move glucose in to the cells to be burned for fuel.

Without an insulin response or glucose, no fat storage happens.

In the same flow, for triglycerides to be broken down to fatty acids and utilized by the body and burned, glucose, insulin, and glycerol-3-phosphate must not be present.

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