Fat is necessary but not in the quantities most Americans consume it. You need it to transport fat-soluble vitamins, insulate you in winter, and cushion your falls. For good health, it’s important to understand and choose the right kind of fat.

Fat is a macronutrient, providing you with a concentrated source of energy and vital calories. The chemical name for this group of nutrients is lipids, and it includes fat, oil, and lecithin. Lipids are found in both plants and animals. In general, when stored at room temperature, fat is solid and oil is liquid.

Fatty Acids

Fatty acids are the building blocks of fat. They are linked together in long chains of carbon and hydrogen atoms. If a fatty acid chain is filled to capacity with hydrogen atoms, it is called saturated. This fat is thick, like butter.

If hydrogen is missing, it is called unsaturated. The amount of missing hydrogen determines whether the fat is monounsaturated or polyunsaturated. This type of fat is thin, as in oil.

All fat, including the fat you find in food, is made of a mixture of saturated and unsaturated fats. The majority of the fat a food contains determines its classification as saturated or unsaturated.

Fat is difficult for your body to digest and utilize because fat and water do not mix. Bile is the key to our utilization of fat. Made by the liver and secreted by the gallbladder, bile can break the triglycerides into their components, fatty acids and glycerol, for absorption.

Saturated Fats

This type of fat is found mainly in animal-based foods. It can easily be identified, because the foods are solid at room temperature. You’ll find saturated fat in meat, butter, cheese, and lard.

These are the most dangerous types of fat because they appear to raise blood cholesterol levels. They may inhibit the liver’s ability to clear out low-density lipoproteins (LDL) and actually stimulate their production. The result is an increased likelihood of atherosclerosis and coronary artery disease.

Saturated fats are found mainly in animals and seldom in plants. The exceptions are palm oil and coconut oil. These plants contain a large amount of saturated fatty acids, which are solid at room temperature. They are free of trans fat, and as such are often encouraged for use in place of hydrogenated oils. Additionally, they are easier for your body to absorb than trans fat.

Unsaturated Fats

These fats are liquid at room temperature. They are generally referred to as oils, and they come mainly from plant sources. These fats have a shorter shelf life, and are more likely to spoil.

There are two types of unsaturated fats: monounsaturated and polyunsaturated. Monounsaturated fats occur in olive, canola, and nut oils, including peanut oil. Polyunsaturated fats include plant oils like safflower, sunflower, cottonseed, sesame, corn, and soybean. Unsaturated fats have been shown to actually lower the low-density lipoproteins (LDL) in your blood.

The only animal oil that is not saturated is polyunsaturated fish oil. These oils contain healthy omega-3 fatty acids, and are an essential part of a healthy diet. If you do not eat fish at least twice a week, it’s a good idea to take fish oil supplements, to ensure you’re getting your omega-3s.

Trans Fat

This is the worst kind of fat. Trans fat has been shown to both lower the good cholesterol, and raise the bad. Not a healthy prospect. To make matters worse, in recent years trans fats have been used extensively in a manufactured foods.

To make hydrogenated fat, extra hydrogen is added to unsaturated vegetable fat. Trans fats and partially hydrogenated fats are listed on labels.

Since trans fats are artificially saturated, the “E” tails of fatty acids are not straight like natural saturated fats, so they do not line up and pack together tightly. You can see this by comparing the way butter (which has no trans fat) and margarine (which is pure trans fat) spread when chilled.