Dear Eating Right: For years I was told that margarine was better for your heart than butter. But recently I heard about a study that found margarine raises cholesterol. Does this mean I should go back to butter? Is tub margarine a problem too?
--MOLLY HOLLIS, Santa Monica
Dear Molly: Although the recently published study in the New England Journal of Medicine appears to be significant, it's too soon to make adjustments in your diet. Perhaps the most important point the study raises is that simply choosing plant fats over animal fats is no longer adequate. We now know that for protection against heart disease, it is important to cut back on fats of all types--polyunsaturated, monounsaturated and especially saturated ones.
It has been proven that saturated fats have a role in raising blood cholesterol, and high blood cholesterol can increase the risk for heart disease. That's why health experts have been urging consumers to substitute vegetable oils and vegetable oil-based margarine and shortening, which are polyunsaturates, for butter and lard, both saturates.
The problem is that many of the polyunsaturates we consume are hydrogenated. This process makes liquid oils into solids (such as margarine, salad dressing and mayonnaise), and the recent study observed that hydrogenation has the same blood cholesterol-raising effect observed in saturates.
In general, the more unsaturated a fat is, the more liquid it is at room temperature and the more susceptible it is to spoilage. During hydrogenation, hydrogen atoms are added to the fat molecules in unsaturated oils (such as corn, cottonseed, soybean or safflower oil). This rearrangement of molecules creates trans-fatty acids, which raise the melting point of the oil and make it more resistant to oxidation and, therefore, less perishable. It also makes the oil more spreadable.
Oils can be hydrogenated at varying degrees depending upon the intended use in food. For example, oils used in processed cakes, cookies, crackers, pie crust, cake mix, shortenings and institutional cooking are partially hydrogenated. So is margarine. But softer margarines require less hydrogenation than stick margarine. Liquid margarine is very lightly hydrogenated, as are tub and diet margarines. Air or water is whipped in during processing to give them their characteristically smooth texture.
The recent study is the first to show that in the body, these reconfigured polyunsaturates--trans-fatty acids--act like saturates: They decrease high-density lipoproteins (the "good" cholesterol) and raise low-density lipoproteins (the "bad" cholesterol). However, the participants in the experiment consumed more trans-fatty acids than the average American normally eats (trans-fatty acids represent only about 3% to 4% of the calorie intake for most Americans). Also, the margarine used was different from margarine consumed in the United States.
For those reasons, Dr. Scott Grundy of the University of Texas Southwestern Medical Center said in an editorial that accompanied the study that while the investigation sheds new light on the impact of trans-fatty acids on human beings, it ". . . further complicates the question of which diet is best for lowering cholesterol levels." Only patients with a high risk for atherosclerosis are advised by the researchers in the study to watch their intake of trans-fatty acids.
For the rest of America, keeping total fat calories to 30% of the day's entire calorie count is still a matter of "trade-offs," says Bettye Nowlin, a registered dietitian and spokesperson for the American Dietetic Assn.
Rather than complete elimination, she suggests that consumers allow no more than 10% of their total calories for saturated fats such as butter and other animal foods. Hydrogenated fats and chocolate should be included in this amount. Then, the remaining fat calories can be divided among monounsaturated and polyunsaturated sources such as olive, peanut, canola, peanut butter and avocado.
"Taste is a factor," Nowlin says. "So you should have a few different fat choices in your head, then you'll know if you make a particular choice on this day, it's OK. It's a mind set."
This recipe for Grilled Swordfish with Creamy Avocado Sauce replaces sour cream- or butter-based sauces with a rich, smooth - tasting avocado sauce made from avocado, nonfat yogurt and chicken broth. Cilantro, lime and garlic add flavor.
\f7 GRILLED SWORDFISH WITH CREAMY AVOCADO SAUCE
3 tablespoons lime juice
3 tablespoons cilantro leaves
1 tablespoon thinly sliced green onion
2 to 3 pounds swordfish fillets
Creamy Avocado Sauce
Combine lime juice, cilantro and green onion in blender container. Blend until well mixed. Season fish to taste with salt and pepper.
Brush with lime juice mixture and grill to desired doneness. Baste occasionally with lime juice mixture. Serve with 2 tablespoons Creamy Avocado Sauce. Makes 8 servings.
Creamy Avocado Sauce
2 medium ripe avocados, mashed
1/2 cup nonfat plain yogurt