Fats are a group of chemical compounds that contain fatty acids. Energy is stored in the body mostly in the form of fat. Fat is needed in the diet to supply essential fatty acids, substances essential for growth but not produced by the body itself. There are three main types of fatty acids: saturated, monounsaturated and polyunsaturated.
All fatty acids are molecules composed mostly of carbon and hydrogen atoms. A saturated fatty acid has the maximum possible number of hydrogen atoms attached to every carbon atom. It is therefore said to be ‘saturated’ with hydrogen atoms.
Some fatty acids are missing one pair of hydrogen atoms in the middle of the molecule. This gap is called an ‘unsaturation’ and the fatty acid is said to be monounsaturated’ because it has one gap. Fatty acids that are missing more than one pair of hydrogen atoms are called ‘polyunsaturated’. Saturated fats (which contain saturated fatty acids) are mostly found in foods of animal origin.
Polyunsaturated fatty acids are of two kinds, omega-3 or omega-6. Scientists tell them apart by where in themolecule the ‘unsaturations’, or missing hydrogen atoms, occur.
Cholesterol is sort of a ‘cousin’ of fat. Both fat and cholesterol belong to a larger family of chemical compounds called lipids. The liver makes all the cholesterol the body needs. It is used to build cell membranes and brain and nerve tissues. Cholesterol also helps the body produce steroid hormones needed for body regulation, including processing food, and bile acids needed for digestion.
People don’t need to consume dietary cholesterol because the body can make enough cholesterol for its needs. But the typical U.S. diet contains substantial amounts of cholesterol, found in foods such as egg yolks, liver, meat, some shellfish and whole-milk dairy products. Only foods of animal origin contain cholesterol.
LDL-cholesterol and HDL-cholesterol act differently in the body. A high level of LDL-cholesterol in the blood increases the risk of fatty deposits forming in the arteries, which in turn increases the risk of a heart attack. Thus, LDL-cholesterol has been dubbed ‘bad’ cholesterol.
The 1992 NIH panel of experts advised that individuals with high total cholesterol or other risk factors for coronary heart disease should have their triglyceride levels checked along with their HDL- cholesterol levels. Triglyceride is another form in which fat is transported through the blood to the body tissues. Most of the body’s stored fat is in the form of triglycerides. Another lipoprotein, very low-density lipoprotein, or VLDL, has the job of carrying triglycerides in the blood. NHLBI considers a triglyceride level below 250 mg/dl to be normal.
It is not clear whether high levels of triglycerides alone increase an individual’s risk of heart disease. However, they may be an important clue that someone is at risk of heart disease for other reasons. Many people who have elevated triglycerides also have high LDL-cholesterol or low HDL-cholesterol. People with diabetes or kidney disease, two conditions that increase the risk of heart disease, are also prone to high triglycerides.
On the other hand, an elevated level of HDL-cholesterol seems to have a protective effect against heart disease. For this reason, HDL-cholesterol is often called ‘good’ cholesterol. Recently a new term has been added to the fat lexicon: trans fatty acids. These are byproducts of partial hydrogenation; a process in which some of the missing hydrogen atoms are put back into polyunsaturated fats. ‘Partially hydrogenated vegetable oils’ such as vegetable shortening and margarine, are solid at room temperature.
At one time, many nutrition experts recommended increasing consumption of monounsaturated and polyunsaturated fats because of their cholesterol-lowering effects.
Now, however, the advice is simply to reduce dietary intake of all types of fat. (Infants and young children, however, should not restrict dietary fat.)
The ‘bottom line’ is actually quite simple, according to John E. Vanderveen, Ph.D., director of the Office of Plant and Dairy Foods and Beverages in FDA’s Center for Food Safety and Applied Nutrition. What we should be doing is removing as much of the saturated fat from our diet as we can. We need to select foods that are lower in total fat and especially in saturated fat. In a nutshell, that means eating fewer foods of animal origin, such as meat and whole-milk dairy products, and more plant foods such as vegetables and grains.