Unsaturated, saturated, and trans fat: the good and the bad

by Steven Kang, M.D. Health Professional

After thoroughly bashing trans fatty acids in my last blog on dietary fat and cholesterol, I thought it only fair to round out the field with a brief comment on fat in general and how it affects cholesterol.

What is fat? Fat is a naturally occurring substance that is made of carbon, hydrogen, and oxygen atoms bonded together. It is one of the highest dietary energy sources available, the other significant sources being sugars and carbohydrates, and it is an essential part of our diet.

Fats are described as saturated or unsaturated, depending upon whether the carbon atoms are full of hydrogen atoms (saturated) or have room for more (unsaturated). This level of saturation determines the physical structure of the fat. For example, animal lard has a high amount of saturated fat and is therefore a solid at room temperature. Olive oil, on the other hand, has a high amount of unsaturated fat is therefore a liquid at room temperature.

To further complicate matters, unsaturated fat can also be described as either mono or polyunsaturated. This just refers to the number of a certain type of chemical bond found in the fat. And lastly, unsaturated fats can be saturated with additional hydrogen atoms and thereby be converted into saturated fats. This process is called "hydrogenation" or "partial hydrogenation" and creates a saturated fat called trans fatty acid.

It has been commonly thought that high fat diets contribute to bad cholesterol levels and increased risks of heart attack, stroke, cancer, and death. As I alluded to in one of my earlier blogs, this not necessarily the case. Why do the people of Crete have one of the lowest rates of heart disease with good cholesterol profiles and yet their diet is very high in fat? The answer lies in the type of fat they are consuming and not necessarily in the amount. The people of Crete eat a tremendous amount of olive oil, a monounsaturated fat. Monounsaturated fats such as olive or canola oil have a good effect on cholesterol by raising the good HDL and lowering the bad LDL.

Polysunsaturated fats which can be found in fatty fish (tuna), shellfish (shrimp), nuts (walnuts), and oils made from safflower, sunflower, corn, or fish also can have a positive effect on cholesterol.

On the other hand, saturated fats have the opposite effect by mainly increasing LDL. These fats are found in red meat, dairy products, and certain oils such as coconut or palm.

Trans fatty acids are the worst offenders and can be found in commercially baked goods (doughnuts, cookies, chips) and fast food. They raise LDL and lower HDL. Remember, high LDL and low HDL have been associated with an increased risk of a heart attack.

In summary, eating fat is not necessarily a bad thing. After all, your body, and likely your taste buds, need it. What's important to keep in mind is you should try to eat the good unsaturated fat, minimize the bad saturated fat, and avoid the ugly trans fat.

How do I know the fat content of what I'm eating? The answer is on the packaging. The FDA requires that the "Nutrition Facts"label breakdown the type and content of fat in food.

A word of caution, though. Remember that fat is a very high energy source and excess consumption of fat will contribute to you becoming fat. Since most of us already are eating a fair amount of fat in our diet, we probably shouldn't try to eat more fat, but rather replace the bad with the good.

Steven Kang, M.D.
Meet Our Writer
Steven Kang, M.D.

Steven Kang, M.D., is a general cardiologist and cardiac electrophysiologist who believes that the best way to treat heart disease is to prevent it. He wrote for HealthCentral as a health professional for Heart Disease, High Blood Pressure, and High Cholesterol.