Good Oils, Bad Oils

Make Sure You Know the Difference

By Sara Tiner

The Chemistry of Oil

Oil is primarily fat, with some trace vitamins and minerals. While that may not sound too impressive, it's an excellent food for our body: Fat is the most efficient source of energy, every cell membrane in the body contains fat, skin and hair are fed with it, and it helps us absorb fat-soluble vitamins. To understand how to make the best oil choices to support our body's needs, we need to delve into how the fats in oil are structured.

Oils are made up of fat, which is (in part) made up of fatty acids. Fatty acids are simply chains of hydrogen and carbon atoms. Fatty acids with only single chemical bonds between carbon atoms are "straighter" and can be packed together tightly, meaning that they're solid at room temperature. These are saturated fatty acids and usually come from animal sources.

Unsaturated fatty acids, usually from vegetable sources, have a double bond between carbons called a "cis" bond. This double bond means the carbon molecules aren't holding onto as many hydrogen atoms as they could. This bond also puts a "kink" in the fatty acid that prevents it from lining up as tightly, so unsaturated fatty acids are liquid at room temperature. If a fatty acid has one double bond it is a "monounsaturated" fatty acid; if it has more than one, it is a "polyunsaturated" fatty acid.

When an unsaturated fat is chemically changed to have a "trans" bond instead of a "cis" bond, it's is called a "trans fat" or "trans fatty acid." This converts it from a liquid into a solid, and it begins to act more like a saturated fat, although it affects health differently. While trans fats do occur naturally, the vast majority are used in processed foods to extend shelf life or improve texture. Trans fats may also be labeled as "hydrogenated" or "partially hydrogenated."

How Fats Function in the Body

Fatty acids are broken apart during digestion and absorbed primarily in the small intestine. They're handled differently from other food components like carbohydrates or proteins. The fat we eat is broken apart into its components (such as triglycerides) and repackaged into "lipoprotein" packets (mixtures of cholesterol, protein and triglyceride). You're probably familiar with the following:

Low-density lipoprotein (LDL) cholesterol or "bad cholesterol" contains the highest amount of cholesterol of the lipoproteins. LDL carries cholesterol from the liver to the rest of the body.

High-density lipoprotein (HDL) cholesterol or "good cholesterol" contains the highest amount of protein of the lipoproteins. HDL picks up cholesterol in the bloodstream and any deposits of LDL and takes it all back to the liver for disposal.

These packets flow into vessels that transport them around the body, where cells can pull the triglycerides or cholesterol from the lipoprotein packets as needed.

How Fats Affect Health

Quantity is key: If too many lipoprotein packets are circulating, they can stick to body tissues (like organs or artery walls). Over time, these deposits can contribute to cardiovascular disease. Additionally, excess fat is stored in fat cells and contributes to health problems associated with obesity.

So, too much fat is bad, but too much "bad" fat can make a bad situation worse. Saturated fats raise HDL, but they also raise LDL. Trans fats actually increase LDL, and research suggests they may also lower HDL and increase triglycerides in the blood. This research is backed up by epidemiological studies suggesting that a diet high in trans fats contributes to heart disease and the risk of developing diabetes. On the other hand, evidence suggests monounsaturated and polyunsaturated fats may protect against these diseases.