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Dietary fats: Know which types to choose
From MayoClinic.com
Special to CNN.com

Most foods contain several different kinds of fat — including saturated, polyunsaturated, monounsaturated and trans fat — and some types are better for your health than others are.

It's not necessary that you completely eliminate all fats from your meals. Rather, choose the best types of fat and enjoy them in moderation.

Fat: A necessary nutrient

Your body needs fat to function properly. Besides being an energy source, fat is a nutrient used in the production of cell membranes, as well as in several hormone-like compounds called eicosanoids. These compounds help regulate blood pressure, heart rate, blood vessel constriction, blood clotting and the nervous system. In addition, dietary fat carries fat-soluble vitamins — vitamins A, D, E and K — from your food into your body. Fat also helps maintain healthy hair and skin, protects vital organs, keeps your body insulated, and provides a sense of fullness after meals (satiety).

But too much fat can negatively impact your health. Eating large amounts of high-fat foods adds excess calories, which can lead to weight gain and obesity. Obesity is a risk factor for several diseases, including diabetes, heart disease, cancer, gallstones, sleep apnea and osteoarthritis. And too much of certain types of fat — such as saturated fat or trans fat — can increase your blood cholesterol levels and your risk of coronary artery disease.

Healthy fats

When choosing fats, your best options are monounsaturated and polyunsaturated fats. These fats, if used in place of others, can lower your risk of heart disease by reducing the total and low-density lipoprotein (LDL) cholesterol levels in your blood. Cholesterol, which your body produces for building cells, is the main substance in fatty deposits (plaques) that can develop in your arteries. Plaques that build up can reduce blood flow through your vessels, increasing your risk of heart disease and stroke.

One type of polyunsaturated fat, omega-3 fatty acids, may be especially beneficial to your heart. Omega-3s appear to decrease the risk of coronary artery disease. They may also protect against irregular heartbeats and help lower blood pressure levels.

Here are the differences among these healthy fats as well as the best food sources for each type:

  • Monounsaturated fat remains liquid at room temperature but may start to solidify in the refrigerator. Foods high in monounsaturated fat include olive, peanut and canola oils. Avocados and most nuts also have high amounts of monounsaturated fat.
  • Polyunsaturated fat is usually liquid at room temperature and in the refrigerator. Foods high in polyunsaturated fats include vegetable oils, such as safflower, corn, sunflower, soy and cottonseed oils.
  • Omega-3 fatty acids are polyunsaturated fats found mostly in seafood. Good sources of omega 3s include fatty, cold-water fish, such as salmon, mackerel and herring. Flaxseeds, flax oil and walnuts also contain omega-3 fatty acids, and small amounts are found in soybean and canola oils.

Harmful fats

Saturated and trans fats are less healthy kinds of fats. They can increase your risk of heart disease by increasing your total and LDL ("bad") cholesterol. Dietary cholesterol isn't technically a fat, but it's found in food derived from animal sources. Intake of dietary cholesterol increases blood cholesterol levels, but not as much as saturated and trans fats, and not to the same degree in all people.

Here are how these fats differ and what their common food sources are:

  • Saturated fat. Usually solid or waxy at room temperature, saturated fat is most often found in animal products — such as red meat, poultry, butter and whole milk. Other foods high in saturated fat include coconut, palm and other tropical oils.
  • Trans fat. Also referred to as trans-fatty acids, trans fat comes from adding hydrogen to vegetable oil through a process called hydrogenation. This makes the fat more solid and less likely to turn rancid. Hydrogenated fat is a common ingredient in commercial baked goods — such as crackers, cookies and cakes — and in fried foods such as doughnuts and french fries. Shortenings and some margarines also are high in trans fat. As of January 2006, food manufacturers are required to list trans fat content on nutrition labels. Amounts less than 0.5 grams per serving is listed as 0 grams trans fat on the food label.
  • Dietary cholesterol. Your body naturally manufactures all of the cholesterol it needs, but you also get cholesterol from animal products, such as meat, poultry, seafood, eggs, dairy products, lard and butter.

A daily limit for fat intake

The U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (HHS) recommend that fat make up no more than 35 percent of your daily calories. This means that if you consume 1,800 calories a day, consume no more than 70 grams of fat a day. (To figure: Multiply 1,800 by 0.35 to get 630 calories, and divide that number by 9, the number of calories per gram of fat, to get 70 grams of total fat.) Keep in mind, however, that this is an upper limit and that most of these fat calories should come from monounsaturated and polyunsaturated sources.

In addition, the USDA and HHS recommend these upper limits for saturated fat and dietary cholesterol for healthy adults:

Type of fat Recommendation
Saturated fat Less than 10 percent of your total daily calories
Dietary cholesterol Less than 300 milligrams a day

Though the USDA and HHS haven't yet established an upper limit for trans fat, they do suggest that you keep your trans fat intake as low as possible. The American Heart Association, on the other hand, has set an upper limit for trans fat — no more than 1 percent of your total daily calories.

Be aware that many foods contain different kinds of fat and varying levels of each type. For example, butter contains unsaturated fats, but a large percentage of the total fat is saturated fat. And canola oil has a high percentage of monounsaturated fat, but also contains smaller amounts of polyunsaturated fat and saturated fat.

Tips for choosing the best types of fat

Limit fat in your diet, but don't try to cut it out completely. Focus on reducing foods high in saturated fat, trans fat and cholesterol, and select more foods made with unsaturated fats. Consider these tips when making your choices:

  • Saute with olive oil instead of butter.
  • Use olive oil instead of vegetable oil in salad dressings and marinades. Use canola oil when baking.
  • Sprinkle slivered nuts or sunflower seeds on salads instead of bacon bits.
  • Snack on a small handful of nuts rather than potato chips or processed crackers. Or try peanut butter or other nut-butter spreads — nonhydrogenated — on celery, bananas, or rice or popcorn cakes.
  • Add slices of avocado, rather than cheese, to your sandwich.
  • Prepare fish such as salmon and mackerel, which contain monounsaturated and omega-3 fats, instead of meat one or two times a week.

Monounsaturated and polyunsaturated fats have few adverse effects on blood cholesterol levels, but you still need to consume all fats in moderation. Eating large amounts of any fat adds excess calories. Fat contains 9 calories per gram, compared with 4 calories per gram for protein and carbohydrates. Also make sure that fatty foods don't replace more nutritious options, such as fruits, vegetables, legumes or whole grains.

  • Trans fat: Avoid this cholesterol double whammy
  • Buying beef? A guide to choosing the leanest cuts
  • Butter vs. margarine: Which is better for my heart?
  • Canola oil: Is it harmful to your health?
  • Low-fat diets: Still beneficial despite study results?
  • Eggs: Are they good or bad for my cholesterol?
  • Healthy diet decisions: Do you know what to eat?
  • June 22, 2006

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