Fats
Fats, or lipids, are vitally important elements of our diet that aid in the absorption of the fat-soluble vitamins (A, D, E, and K) and provide energy reserves, insulation, and protection for the body. You might be thinking, "If fat is so important to health, why do nutritionists always talk about the danger of too much fat in the American diet?"
The problem lies in the types and quantity of fat that most Americans consume. Many health problems, such as obesity, diabetes, some forms of cancer, and heart disease, are associated with excessive fat intake, particularly the saturated fats found in meat and butterfat as well as in hard margarine, commercially fried foods, and most processed food. A few saturated fats come from plant sources, such as palm, palm kernel, and coconut oils, and cocoa butter. Some sources estimate that average Americans consume over 40% of their daily caloric intake from fat, or between 900 and 1,350 calories daily. Nutrition experts recommend limiting our total fat consumption to the more appropriate range of 10-30% (we recommend 20%) and reducing the amount of saturated fat to below 5%.
Dietary lipids include cholesterol and three kinds of fats: saturated, polyunsaturated, and monounsaturated fatty acids. Only saturated fats, along with cholesterol itself, raise blood cholesterol. Cholesterol in the diet primarily comes from animal sources: meats, eggs (only the yolks), dairy (fat-free products have only very small amounts), fish, and poultry. Experts agree that Americans should reduce their daily intake from around 500 mg daily to 300 mg daily, or slightly more than the amount in one extra-large egg.
Vegetable fats such as grain, seed, and nut oils tend to be less saturated and less harmful than animal fats such as butter and lard, but they are equally calorie-dense. Research has proven that polyunsaturated fats help the body get rid of newly formed cholesterol and reduce cholesterol deposits in artery walls. Monounsaturated fats also reduce blood cholesterol, but only when the overall diet is very low in saturated fat. In order to realize these risk-reducing benefits, it is imperative that you reduce your intake of all types of fat. If you are on a weight-loss regimen, it is also very important to limit all fats to no more than 20% of total calories, which is equal to 240 calories on a 1200-calorie diet. This amounts to about 27 grams of total fat, or 2.5 tablespoons per day.
Another reason to reduce fats in the diet has to do with a fatty acid called arachidonic acid. This substance may aggravate inflammatory reactions that worsen joint pain and stiffness and at locations in the arteries that have been previously damaged by plaques (hardened deposits of fat and cholesterol that stick to the sides of the arteries and reduce blood flow). Animal fats such as butter, lard, and meat fat contain high amounts of this acid, and the common vegetable oils such as corn, sunflower, and safflower are easily converted to the same arachidonic acid. This is one reason why I recommend using monounsaturated oils, such as olive, canola, or peanut oil, instead of other vegetable oils. "Extra-virgin" olive oil has an additional benefit of providing some antioxidant protection. (Antioxidants are nutrients that join with so-called "free radicals," or unattached oxygen molecules, to prevent them from enlarging plaques.)
Experts agree that hydrogenated fats found in processed vegetable oils can raise blood cholesterol, particularly when the processing produces trans fatty acids. Foods most likely to contain too much trans fatty acids are hard margarines, vegetable shortening, and frying oil, especially in commercial bakeries and restaurants. Hydrogenation is a process whereby liquid vegetable oil becomes more saturated and chemically modified to become more stable. The advantage to food processing companies and fast-food establishments is that these more stable oils have a long shelf life, they can be used for high temperature cooking, and they become more solid, like butter. Many commercial food products contain hydrogenated or partially hydrogenated vegetable oils.
Some people believe that no table is completely set without butter or margarine, and few restaurants fail to deliver one or the other with the complimentary bread basket. Unfortunately, in either case, it is a food likely to increase cholesterol. Some newer margarines are now manufactured with more liquid oil to reduce trans fatty acid content, but few people need more of such oils in their diet. Brands vary widely in cholesterol-raising saturated and trans fat content due to full to partial hydrogenation; besides, margarine has the same calorie content as butter.
You must have heard our message by now: Reduce fat! If you cannot face life without yellow spread on bread, limit its use as much as possible. And when you must have it, use the more liquid or tub margarines rather than stick forms.
You may have heard about omega-3 fatty acids and their importance to health. The body requires two essential fatty acids for adequate biological function: linoleic acid and linolenic acid, collectively referred to as Vitamin F. They are both polyunsaturated fats contained in plant oils, nuts, and seeds. They are usually found together in food sources, although specific foods have higher concentrations of one over another. The body generally requires more linolenic acid (omega-3) than linoleic acid (omega-6), in a ratio of about 2:1, but the vast proportion of the two in the diet consists of the omega-6 fats from common vegetable oils such as corn, safflower, and sunflower.
Linolenic acid is important to heart health, because it is the precursor of two other omega-3 fatty acids (abbreviated as EPA and DHA) found in fish oils. Populations that consume large quantities of fish seem to have a lower incidence of heart disease, presumably due to higher intake of these two omega-3 fatty acids, though there are many other lifestyle and diet differences that also may contribute to the better heart health. The omega-3 fatty acids are precursors in the body of prostaglandins: hormone-like substances that affect the inflammatory process and may help to reduce plaques in the arterial walls. They also reduce the risk of the formation of blood clots, help to lower cholesterol and triglyceride levels, and raise HDL cholesterol. The body can metabolize linolenic acid into EPA. Although this conversion is not 100% efficient, individuals who do not eat fish can substitute a teaspoon per day of plant seed oil, such as flaxseed, that contains linolenic acid. Check food labels for good sources of it (often abbreviated ALA, for alpha-linolenic acid). It is also found in dark green leafy vegetables, pumpkin seeds, walnuts, and several beans, including soy, kidney, lima, navy, and great northern.
A word of caution: digestion of the common omega-6 vegetable oils uses the same enzymes that are needed to convert linolenic acid to EPA, so you also need to decrease your consumption of those oils. Substituting olive, canola, and peanut oil for corn for other vegetable oils is the best way to do this, and it is consistent with obtaining the majority of your dietary fat from unsaturated sources.