Sorting Out the Fats

Our health is influenced by both the amount and the type of fat that we eat. Fats are molecules; they are classified according to the chemical structures of their component parts. But you don't need to be a chemist to understand the connection between the various fats in foods and the effect these fats have on the risk for disease. Some definitions will help.

Dietary fats, or triglycerides, are the fats in foods. They are molecules made of fatty acids (chain-like molecules of carbon, hydrogen, and oxygen) linked in groups of three to a backbone called glycerol. When we eat foods that contain fat, the fatty acids are separated from their glycerol backbone during the process of digestion.

Fatty acids are either saturated or unsaturated, terms that refer to the relative number of hydrogen atoms attached to a carbon chain. Fat in the foods that we eat is made up of mixtures of fatty acids—some fats may be mostly unsat-urated, whereas others are mostly saturated (see sidebar: A Comparison of Fats, page 27).

Monounsaturated fatty acids are fatty acids that lack one pair of hydrogen atoms on their carbon chain. Foods rich in monounsaturated fatty acids include canola, nut, and olive oils; they are liquid at room temperature. A diet that provides the primary source of fat as monounsaturated fat (frequently in the form of olive oil) and includes only small amounts of animal products has been linked to a lower risk of coronary artery disease. This type of diet is commonly eaten by people who live in the region surrounding the Mediterranean Sea (see Chapter 1, page 14).

Polyunsaturated fatty acids lack two or more pairs of hydrogen atoms on their carbon chain. Safflower, sunflower, sesame, corn, and soybean oil are among the sources of polyunsaturated fats (which are also liquid at room temperature). The essential fatty acids, linoleic and linolenic acid, are polyunsaturated fats. Like monoun-saturated fats, polyunsaturated fats lower blood cholesterol levels and are an acceptable substitute for saturated fats in the diet.

Saturated fatty acids, or saturated fats, consist of fatty acids that are "saturated" with hydrogen. These fats are found primarily in foods of animal origin—meat, poultry, dairy products, and eggs—and in coconut, palm, and

A Comparison of Fats

U Percent polyunsaturated fat

Percent monounsaturated fat

Percent saturated fat

Canola Safflower Sunflower Corn oil Olive oil Soybean Peanut Chicken oil oil oil* oil oil fat

Lard Palm oil Beef fat Butterfat Coconut oil

*Total is not 100% because of the presence of other, minor fat compounds.

palm kernel oil (often called "tropical oils"). Foods that are high in saturated fats are firm at room temperature.

Because a high intake of saturated fats increases your risk of coronary artery disease, nutrition experts recommend that less than 10 percent of your calories should come from saturated fats. To find out how to calculate your fat allowance, see the sidebar Recommended Fat Intake, page 28, and to determine the total and saturated fat contents of some foods, see the sidebar Where's the Fat? page 28.

Omega-3 fatty acids are a class of polyunsaturated fatty acids found in fish (tuna, mackerel, and salmon, in particular) and some plant oils such as canola (rapeseed) oil. These fatty acids have made the news because of the observation that people who frequently eat fish appear to be at lower risk for coronary artery disease. Omega-3 fatty acids also seem to play a role in your ability to fight infection.

Hydrogenated fats are the result of a process in which unsaturated fats are treated to make them solid and more stable at room temperature. The hydrogenation process, which involves the addition of hydrogen atoms, actually results in a saturated fat. Trans-fatty acids are created by hydrogenation. An increase in consumption of these fats is a concern because they have been associated with an increased risk of coronary artery disease. Hydrogenated fat is a common ingredient in stick and tub margarine, commercial baked goods, snack foods, and other processed foods.

Cholesterol is a waxy, fat-like substance that is a necessary constituent of cell membranes and serves as a precursor for bile acids (essential for digestion), vitamin D, and an important group of hormones (the steroid hormones). Our livers can make virtually all of the cholesterol needed for these essential functions. Dietary cholesterol is found only in foods of animal origin, that is, meat, poultry, milk, butter, cheese, and eggs. Foods of plant origin, that is, fruits, vegetables, nuts, seeds, legumes, grains, and the oils derived from them, do not contain cholesterol. Eggs are the food most often associated with cholesterol, because the average large egg contains about 210 milligrams of cholesterol (only in the yolk), and the recommended daily cholesterol intake is 300 mg or less. However, for most people, meat contributes a higher proportion of cholesterol to the diet than do eggs, because cholesterol is found in both the lean and fat portions

Recommended Fat Intake

Health experts recommend consuming no more than 30percent of our calories from fat—with no more than 10percent from saturated fat. Here is a chart to help you determine how much fat you should eat.

Calories

Total Fat (grams)

Saturated Fat (grams)

Most women & older adults

About 1,600

S3

Less than 17

Most men, active women, teen girls & children

About 2,200

73

Less than 24

Active men & teen boys

About 2,S00

93

Less than 31

Note: These are guidelines for healthy individuals. If you have heart disease or high blood cholesterol or triglyceride levels, or if you are overweight, ask your health care professional to recommend the types of fat and amounts most appropriate for you.

of meat. Shellfish have acquired an undeserved reputation for being high in cholesterol. Their cholesterol and total fat contents are actually comparatively low (see sidebar: Cholesterol Content of Foods, page 29).

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