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Miriam E. Nelson, Ph.D Responds:
Miriam E. Nelson, PhD, of Tufts University and the best-selling author of the Strong Women book series, responds: We all need fat in our diets—even those of us trying to lose weight. Fat supplies essential nutrients, helps absorb fat-soluble vitamins, and aids with satiety. Because it carries flavor and breaks down more slowly than protein or carbohydrates, fat can actually help us feel full longer after a meal. But fat becomes a problem when we eat too much of it. Unfortunately, that's easy to do, because fat is more calorie-dense than protein or carbohydrates; fat contains 9 calories per gram, while carbs and protein contain 4. The type of fat also matters. Certain fats have health-promoting properties, so it's worthwhile to choose those. Here's what you need to know about the fundamental types of fats.
Saturated fats are solid or almost solid at room temperature and come mostly from animal and dairy products, but also some plant sources. Diets high in saturated fat may increase cholesterol, which is a risk factor for heart disease. Butter, lard, and palm oil contain mostly saturated fat.
Trans fatty acid is vegetable oil that has been made solid by a manufacturing process called hydrogenation. (Look for “hydrogenated vegetable oil” on the label.) In the body, trans fatty acids have effects similar to those of saturated fats. That is why there is little health difference between “stick” butter, which contains saturated fats, and “stick” margarine, which contains trans fatty acids. Baked goods, fried foods, chips, and crackers may also have trans fatty acids.
Monounsaturated fat is liquid at room temperature, but becomes partly firm if chilled. Many experts believe that substituting monounsaturated fat for saturated fat in the diet promotes improved cholesterol levels. Olive oil and olives, avocados, and canola oil contain monounsaturated fat.
Polyunsaturated fat is liquid unless you put it in the freezer. Most important is that it also appears to have health-promoting properties. Omega-3 fatty acid is probably the most well-known polyunsaturated fat. Scientists believe that omega-3 fatty acids may reduce the risk of blocked blood vessels and heart attacks by preventing platelets from clotting and sticking to artery walls. Foods that contain omega-3s are flaxseed, walnuts, soybeans, and cold-water fish such as salmon, sardines, lake trout, albacore tuna, and mackerel.
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Miriam E. Nelson
Ph.D
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