All Fats Are Not Created Equal

By:
Nancy Snyderman, M.D.

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We need a little fat in our diets for good health, and some fats are better for you than others. Fatty acids, the building blocks for fat, are divided into three chemical classes according to their hydrogen content: saturated, monounsaturated, and polyunsaturated. Here’s a rundown.

Saturated Fatty Acids

Saturated fats are the main culprit in raising low- density lipoproteins (LDL, or “bad” cholesterol). They are found primarily in meats and dairy products. Many of these foods also contain cholesterol. Cutting down on saturated fat means going easy on beef, veal, lamb, pork, beef and poultry fat, butter, cream, whole milk, and cheeses as well as other dairy products made from whole milk. Saturated fatty acids are also found in plant-based products, including palm and coconut oils and cocoa butter. The American Heart Association recommends that you limit your saturated fat intake to less than 10 percent of total calories each day. The less the better. This is a “bad” fat.

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Polyunsaturated Fats

These are typically found in the liquid oils that come from vegetables. Common sources include sesame, sunflower, and safflower oils; sunflower seeds; and corn and soybeans and their oils. Only the polyunsaturated fats are considered “essential,” meaning they cannot be manufactured by the body. Like minerals and vitamins, they must be ingested as food. If we don’t eat enough, then we won’t get enough. And that would be unfortunate, for these compounds—principally linoleic acid and linolenic acid— are vital to the maintenance of cell membranes and to the manufacture of potent chemical messengers that regulate everything from blood pressure to the firing of nerves.

When essential fatty acids are in short supply, the body compensates by substituting other types of fatty acids that have a less supple biochemical structure. As polyunsaturates are replaced by these other compounds, cell membranes become more rigid, leading to progressive hardening of the arterial walls. Polyunsaturated fats should make up 10 percent or less of your total daily calories. They are “good” fats.

I should also emphasize another type of essential polyunsaturated fat: omega- 3 fatty acids. These are found in fatty fish, like salmon, tuna, and trout, as well as in canola oil and flaxseed. Known as eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA, they help maintain and protect your heart, blood vessels, and brain function. Two fish meals a week will supply you with the right amount of these fats.

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Monounsaturated Fatty Acids

Monounsaturated fats come from avocados and olive, canola, and peanut oils, as well as from nuts. For more than thirty- five years, studies have shown that diets containing monounsaturated fats, such as the traditional Mediterranean diet, are good for the heart. These fats can help lower cholesterol, blood pressure, and blood sugar levels.

The Mediterranean diet is moderately high in fat (about 30 percent of fat calories mostly from olive oil) and emphasizes fresh fruits and vegetables, whole grains, legumes, nuts, and a high intake of fish and little red meat. If your HDL (high- density lipoprotein, or “good”) cholesterol is low (35 or less), add a daily serving or two of canola or olive oil, nuts, avocado, or fatty fish (like salmon). In exchange, subtract a serving or two of sweets or refined bread, pasta, crackers, or cereal.

These “good” fats should make up about 15 percent of your total calories. Both polyunsaturated and monounsaturated fats are better than saturated fats because they may aid in lowering cholesterol. But remember they are fats and should still be used sparingly. They are not a license to add oil; their calories do count.

Trans Fats

One type of bad fat to eliminate entirely is trans fat, also known as partially hydrogenated vegetable oil. Trans fats are formed during a process called hydrogenation, which transforms liquid oil into shelf- stable solid fat. Trans fats clog arteries, and are found in many packaged cookies, crackers, snacks, and other processed foods.

 

Excerpted from:
Diet Myths That Keep Us Fat by Nancy Snyderman, M.D.
© 2009, Crown.

 

 

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