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What Do Fats Do in the Body?

Lipid droplets

These lipid droplets store fat in the cells of the tobacco hornworm, Manduca sexta.
Photo: Estela Arrese.

To Find Out More

When you have your cholesterol checked, the doctor typically gives you your levels of three fats found in the blood: LDL, HDL and triglycerides. High levels of LDL and triglycerides can lead to disease, and a healthy diet involves watching how much fatty food we eat. However, our bodies need a certain amount of fat to function—and we can't make it from scratch.

Triglycerides, cholesterol and other essential fatty acids—the scientific term for fats the body can't make on its own—store energy, insulate us and protect our vital organs. They act as messengers, helping proteins do their jobs. They also start chemical reactions that help control growth, immune function, reproduction and other aspects of basic metabolism.

The cycle of making, breaking, storing and mobilizing fats is at the core of how humans and all animals regulate their energy. An imbalance in any step can result in disease, including heart disease and diabetes. For instance, having too many triglycerides in our bloodstream raises our risk of clogged arteries, which can lead to heart attack and stroke.

Fats help the body stockpile certain nutrients as well. The so-called "fat-soluble" vitamins—A, D, E and K—are stored in the liver and in fatty tissues.

Knowing that fats play such an important role in many basic functions in the body, researchers funded by the National Institutes of Health study them in humans and other organisms to learn more about normal and abnormal biology.

Despite fat's importance, no one yet understands exactly how humans store it and call it into action. In search of insight, Oklahoma State University biochemist Estela Arrese studies triglyceride metabolism in unexpected places: silkworms, fruit flies, and mosquitoes.

The main type of fat we consume, triglycerides are especially suited for energy storage because they pack more than twice as much energy as carbohydrates or proteins.

Once triglycerides have been broken down during digestion, they are shipped out to cells through the bloodstream. Some of the fat gets used for energy right away. The rest is stored inside cells in blobs called lipid droplets. When we need extra energy—for instance, when we run a marathon—our bodies use enzymes called lipases to break down the stored triglycerides. The cell's power plants, mitochondria, can then create more of the body's main energy source: adenosine triphosphate, or ATP.

Arrese works to identify, purify, and determine the roles of individual proteins involved in triglyceride metabolism. Her work could teach us more about disorders like diabetes, obesity, and heart disease. But before any of that can happen, says Arrese, "We need to study a lot and have information at the molecular level."

Thanks to the National Institute of General Medical Sciences ( (NIGMS), part of the National Institutes of Health (, for supplying this article.

Measuring Cholesterol Levels

Everyone age 20 and older should have his or her cholesterol measured at least once every five years. A blood test called a lipoprotein panel can help show whether you're at risk for coronary heart disease by looking at substances in your blood that carry cholesterol. This blood test is done after a 9-to-12-hour fast (no eating) and gives information about your:

  • Total cholesterol—a measure of the total amount of cholesterol in your blood, including low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol.
  • LDL (bad) cholesterol—the main source of cholesterol buildup and blockage in the arteries
  • HDL (good) cholesterol—HDL helps remove cholesterol from your arteries
  • Triglycerides—another form of fat in your blood that can raise your risk for heart disease

See how your cholesterol numbers compare to the table below:

Total Cholesterol Level


Less than 200mg/dL


200-239 mg/dL

Borderline high

240mg/dL and above


LDL (Bad) Cholesterol Level

LDL Cholesterol Category

Less than 100mg/dL



Near optimal/above optimal

130-159 mg/dL

Borderline high

160-189 mg/dL High
190 mg/dL and above Very High

HDL (Good) Cholesterol Level

HDL Cholesterol Category

Less than 40 mg/dL

A major risk factor for heart disease

40—59 mg/dL

The higher, the better

60 mg/dL and higher

Considered protective against heart disease

Spring 2013 Issue: Volume 8 Number 1 Page 20-21