Fats are lipids. These compounds tend to be oily or waxy, and are not soluble in water. They include:

• fats, which tend to be solid
• oils, which are liquid
• and cholesterol

Gram for gram, fats produce slightly more than double the amount of energy that carbohydrates produce. Lightweight and energy dense, fat burns slowly and gives off an enormous amount of heat energy. Every gram of fat burned creates 9 calories of heat energy.

If people stored all their energy reserves in carbohydrates, our bodies would be much larger than they are! That is because fats contain no water in their molecules, whereas carbs are carbon plus water.

Think of diving into a pool with your clothes and running shoes still on. Those clothes seemed to weigh nothing when dry but are an enormous burden when wet! Glycogen, the storage form of carbohydrates, is much bulkier than fat.

Other Functions
Besides storing energy, fats, cholesterol and other lipids perform many vital functions. Cholesterol is the chemical backbone for sex hormones such as estrogen and testosterone, anti-inflammatory hormones such as cortisol, and bile needed for fat digestion. The layer of fat under the skin provides a thermal blanket for the body much like the insulation in your attic. Fats are also required for the absorption and storage of the fat-soluble vitamins, A, D, E and K. People who consume extremely low fat diets may be susceptible to deficiencies in these vitamins. Fats are responsible for the particular mouth feel and flavour of many foods. They also contribute to a feeling of fullness, a signal to stop eating.

After energy storage, the most critical role that fats play is in the formation of cellular membranes. All the membranes in the cell are composed mainly of compound fats called phospholipids and cholesterol. These membranes are the site for energy production within the cell and protein production. They also serve as the gatekeepers for the entry of nutrients and the exit of toxic wastes. Phospholipids are also involved in blood-clotting.

Saturated and Unsaturated Fats
Fats are composed of fatty acids joined to a small molecule called glycerol. Each glycerol molecule can hold up to three fatty acids. When it contains three fatty acids it is called a triglyceride. Fat is stored in our body in the form of triglycerides. Your doctor may decide to measure the amount of triglycerides in your blood when you go for a physical examination. Fatty acids are straight chains of carbon atoms. The chains can be anywhere from 4 to 22 carbon atoms long. Saturated fatty acids, the ones you should limit in your diet, contain as many hydrogen atoms as the carbons can hold on to. In other words, the carbon chain is saturated with hydrogen. If any of those hydrogen atoms are removed, the fatty acid becomes unsaturated.

One double bond in a fatty acid makes it monounsaturated. More than one and it is polyunsaturated. Olive oil is monounsaturated oil and corn oil is polyunsaturated. Saturated fats are very stable, do not change when heated, and do not easily go rancid. Unsaturated fatty acids are vulnerable to attack by heat, light, moisture and air. Most of the fats found in foods have a combination of saturated and unsaturated fatty acids. The fats of animals are mostly saturated. Saturated fats are found in beef, pork, dairy products, lamb, and chicken.

Vegetable oils that have been hydrogenated, or hardened, to create shortening and most margarines, are saturated. Hydrogenation creates trans fats, which are not made by the body and have no known health benefits. These unsaturated fats have been straightened out at the double bonds. By altering the essential shape of the molecules, trans fats are biologically inactive, and detrimental to health. They act more like saturated fats, sticking to artery walls. Plants tend to have unsaturated fats with the exception of tropical oils. Since palm and coconut trees are exposed to extreme heat, humidity, and intense sunlight in their tropical setting – all conditions that can damage double bonds – nature gave them saturated fats without double bonds!

Although tropical oils are saturated, they contain medium-chain fatty acids and micronutrients that support well being. Their major fatty acids are used for energy nearly as quickly as sugars, and are less likely to be stored as fat. You can probably find 100% palm oil at your local health food store, labeled as "trans-fat free, organic shortening."

Essential Fatty Acids
If most of the fats in our bodies are saturated fats, then why are we told to limit saturated fats and eat unsaturated fats instead?

Humans can manufacture all but two of the fatty acids our bodies require, using excess carbohydrates and protein. These two fatty acids, linoleic acid and linoleic acid, are called Essential Fatty Acids (EFAs) because they are essential to health and must be obtained from the diet. Both are polyunsaturated and found in plant foods. Once again we are dependent on plants for essential nutrients. Good sources are whole grains, seeds, nuts, dried beans, and dark green leafy vegetables.

Polyunsaturated oils pressed from corn, sunflower, sesame, soybean and flaxseed are potentially excellent sources of EFAs. Unfortunately, once these oils are pressed, they are very perishable. For example, whole flax seeds can be safely stored in a cool, dry place for up to one year, but flax oil must be refrigerated in a dark container and used within two weeks of opening.

To extract seed oils and prevent spoilage, food processors put cooking oils through an extensive process of heating, bleaching and deodorizing. To ensure a nutritious product, look for cold-pressed polyunsaturated oils. Do not use these oils for cooking. Keep them refrigerated in dark containers. They make excellent oils for salad dressings. For cooking, monounsaturated, cold-pressed extra virgin olive oil is a delicious and healthy choice. The best advice – get your EFAs (essential fatty acids) from whole foods. Eating rancid or altered fats is worse than eating saturated fats.

The Cholesterol Conundrum
There are two sources of this waxy-like substance – the cholesterol we consume in our diet, obtained only in animal products, and the cholesterol produced by the liver. Cholesterol is essential for good health yet we are bombarded by news about its health hazards. High levels of blood cholesterol are a serious risk factor in heart disease and stroke. Then we’re told there is “good cholesterol” and “bad cholesterol.”

Our brains do not work very well without cholesterol. And without cholesterol, our body cannot make several hormones, bile for digestion or cell membranes. Since cholesterol and triglycerides are not soluble in the watery medium of the blood, they are transported by a class of compounds called lipoproteins, which prevents them from floating to the surface like the oil in an oil and vinegar salad dressing.

There are different types of lipoproteins. All contain cholesterol and triglycerides at the centre and an outer coating of protein and phospholipid to make them soluble. They differ in the amounts of these components. HDL (high density lipoprotein), or the “good cholesterol” contains the most protein and the least cholesterol and triglyceride. LDL (low density lipoprotein) or “bad cholesterol” contains comparatively more cholesterol and triglyceride and less protein.

To help yourself remember which is better, think of keeping your “LDL Low” (low because it’s the bad one) and “HDL High” (high because it’s the good one). LDL cholesterol carries cholesterol and triglycerides to the cells to produce hormones or energy or membranes, etc. Unfortunately, LDL cholesterol seems to have a greater tendency to attach to artery walls, contributing to arteriosclerosis, or hardening of the arteries. About 50% of all cholesterol is transported by LDL. HDL cholesterol acts in the opposite direction, picking cholesterol up from artery walls and returning it to the liver. There it is incorporated into bile, and begins its journey out of the body through the intestinal tract. As you can see, both types of cholesterol are necessary to good health, but like everything else in nature, it is the balance that is important.

Cholesterol & Saturated Fats–the Connection
Diets high in saturated fats and cholesterol have been associated with increased risk of heart disease. Health authorities advise us to decrease the total amount of dietary fat, and especially cut down on saturated fats and cholesterol. What is the link when cholesterol contains no fatty acids at all, saturated or unsaturated, and in fact it is a completely different type of lipid?

There is a reason for the recommendation. A diet high in saturated fat seems to encourage the liver to produce more cholesterol internally. This leads to an increase in LDL or “bad cholesterol.” The Omega 3 oils in cold-water fish and some seed oils such as flaxseed or hemp oil seem to increase levels of HDL and decrease levels of LDL. Beware of products that advertise “cholesterol free.” They may still be very high in total fat, and if they contain hydrogenated vegetable oils, they may be high in trans fats too, which are detrimental to health.