What is Fat?

What is Fat?

Fat belongs to the group of nutrients called lipids and they are available in three forms. Fat is the preferred fuel source during aerobic activities.

What Is Fat?

Fat belongs to the group of nutrients called lipids and they are available in three forms but only one yields energy, triglycerides!

Stored body fat is an ideal fuel source for aerobic metabolism (long duration/low-to-medium intensity exercise) since fat has the highest energy density (9kcal/g). The three forms of lipids are:

  1. Triglycerides
  2. Phospholipids
  3. Sterols


Triglycerides are fats and oils and in foods 95% of fats are triglycerides. In the body 99% of fats are stored as triglycerides!

They are composed of 3 fatty acids (OH) attached to 1 glycerol (“ol” = alcohol) molecule and fatty acids are the primary type of fat used by muscle cells during aerobic metabolism.

Fatty acids are stored in the body as triglycerides and triglycerides are mainly stored in fat cells and to a lesser degree in skeletal muscle cells.

If need be, triglycerides can be broken down into fatty acids and glycerol as a source of energy. This process is called lipolysis (triglycerides → 3 fatty acids + 1 glycerol).

The enzymes that control lipolysis are called lipases. The glycerol portion of lipolysis is not a direct form of energy but the liver uses the glycerol to synthesize glucose, which of course yields energy.


What Is Fat?
What Is Fat?

Phospholipids are not a source of energy used by the body during exercise. Instead, they provide an insulating layer around nerve cells!

Lecithin is an emulsifier, a substance that allows mixing of water and oil. It is present in cell membranes and helps fat moving in and out of the cells because phospholipids are water – and fat-soluble.

Phospholipids allow fat-soluble substances, like hormones and vitamins, to pass easily in and out of cells.


Sterols do not provide any energy during exercise. They are alcohol derivates with a steroid ring structure and the most famous sterol is cholesterol.

Foods derived from both plants and animals contain sterols but only those sterols derived from animals contain cholesterol!

“Good” cholesterol does not refer to a type of cholesterol found in foods. “Good” cholesterol refers to how the body transports cholesterol in the blood!

Cholesterol is not some bad ingredient of food but a compound made by the body (the liver) and used by the body. The cholesterol that is made in the body is called endogenous (“endo” = within; “gen” = arising). Cholesterol that comes from outside the body is called exogenous (“exo” = outside the body).

The liver produces its own cholesterol (800 – 1500mg/day) and the daily value of cholesterol that should be consumed is 300mg/day. So, the liver actually produces most of the daily cholesterol needs itself!

Excessive amounts of cholesterol in the blood can clock the arteries, a disease called atherosclerosis (athero = “porridge or soft”; scleros = “hard”; osis = “condition”) that causes heart attacks and strokes!

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What is Glycogen?
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