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The Final (Maybe) Verdict on the Low-Fat Diet

Whoever said that nothing is simple must have been thinking about fats in the diet. You've been told often enough that "low-fat" is the key to a heart-healthy diet—meaning that fat should provide less than 30% of your total calories. But how can you make such a calculation? Unless you have a dietician in residence, it's impossible to figure out what your total calorie intake is, let alone what percentage of those calories comes from fat. It's just as hard to know which fats you eat: maybe you keep canola or olive oil in your pantry, but what's in all those restaurant meals you eat?

And you've undoubtedly heard some experts say that oils such as olive and canola are heart-protective, since they are rich in monounsaturated fats. In September, in fact, the American Heart Association (AHA), the most influential backer of low-fat eating, fine-tuned its advice on fats to allow for more monounsaturated fat—at least under some circumstances—because of its potential health benefits. Does this mean you should eat more of these oils?

Make up your minds already!

Nutrition experts don't agree about the benefits of the standard low-fat, high-carbohydrate diet. There is some evidence that, in some people, this kind of diet over the long term promotes high blood sugar levels and high triglycerides (fats in the blood) and lowers HDL ("good") cholesterol. Thus, some nutritionists have been recommending eating more monounsaturated oils, not more carbohydrates. They cite the example of Italy, where the typical diet is rich in monounsaturated fats (mostly from olive oil) and heart disease rates are low.

Other researchers insist that consuming too much of any fat is bad, since fats are high in calories and thus promote obesity. Some actually recommend a very-low-fat diet, with less than 15% of calories derived from fat. Dr. Dean Ornish and others belong to this school of thought. They, in turn, point to Japan and China, where fat intake and heart disease rates are low. Studies have shown that very-low-fat diets can help treat those who already have heart disease.

The WELLNESS LETTER has always agreed with the AHA's long-standing advice, recommending a diet low in fat (less than 30% of calories from fat) and rich in carbohydrates. We do agree with the association's new advice about monounsaturated fats.

What does this mean for you?

For most people, it's best to stick to a low-fat diet, with the following nuances:

• The bulk of your calories should come from carbohydrates—provided by fruits, whole grains, legumes, vegetables, and nonfat or low-fat dairy products, not by sugary, highly processed foods. Eat small servings of skinless chicken and turkey breast and/or lean meat. You needn't give up high-fat foods such as cheese, but eat them only occasionally and in small amounts.

• Be careful about the kind of fat you consume. The AHA has long recommended that less than one-third of your fat calories should come from saturated fatty acids, less than one-third polyunsaturated, and the rest monounsaturated (see box at right for more about these kinds of fats). Now it emphasizes reducing saturated fats even more and replacing them with monounsaturated fats. Exact calculations are impossible in real life, but you can move in the right direction, for instance, by replacing butter with a highly monounsaturated oil such as canola or olive oil (or peanut, walnut, or almond oil). All it takes is a small change: replacing just two tablespoons of butter with the same amount of olive or canola oil may be enough to shift your daily fat balance to meet the new AHA recommendation. Small amounts of peanuts, almonds, or peanut butter are also healthy choices.

• Eat fish once or twice a week, for its heart-protective omega-3 fatty acids (polyunsaturated). Also consume some foods rich in the omega-3 called alpha-linolenic acid—studies suggest that it also helps protect the heart (see WELLNESS LETTER, May 1999). Not many foods are rich in alpha-linolenic acid—only canola, flaxseed, and soybean oils, as well as walnuts and walnut oil. In a recent study, women who consumed the equivalent of a daily tablespoon of canola oil, half an ounce of walnuts, or a little ground flaxseed had a one-third to one-half lower risk of a fatal heart attack than those consuming little alpha-linolenic acid.

• Limit your intake of hydrogenated oils, found in many packaged foods, including stick margarine, puddings, crackers, cookies, and potato chips. Hydrogenation makes some of the unsaturated fats more saturated, and also results in "trans fats," which act like saturated fat, boosting blood cholesterol and increasing the risk of heart disease. Manufacturers hydrogenate—that is, add hydrogen to—highly polyunsaturated vegetable oils in order to give them (and the processed foods made with them) a more solid consistency and a longer shelf life. It's nearly impossible to tell exactly how much trans fat you're eating, since it isn't listed on food labels. That will change, probably in the year 2001, because the FDA recently announced that it plans to require food makers to list the amount of these fats on labels.

Bottom line: If the standard low-fat diet seems to be keeping you healthy, that's great. But if, despite it, you have high triglycerides or low HDL, or if you are diabetic or are at high risk for diabetes or heart disease, see if consuming more canola or olive oil helps. Just don't go overboard: eating like an Italian doesn't mean simply adding tablespoons of olive oil to your American-style meals. The oil has to replace other fats—otherwise you'll gain weight, which would cancel out the potential heart benefits. Nuts and avocados are other good sources of monounsaturates.

What about all those trendy high-fat diets? See our article on the Atkins diet.

Fat is not fat is not fat

All fats are combinations of saturated and unsaturated fatty acids, which is why fats are described with terms such as "highly saturated" or "highly polyunsaturated." For instance, only about half the fatty acids in beef are saturated, but that's a high proportion. Fatty acids vary in length and in degree of saturation (that is, how many hydrogen atoms they carry), both of which help determine whether a fat is solid or liquid (oil) at room temperature.

Saturated fatty acids carry all the hydrogen atoms they can hold. Highly saturated fats come chiefly from animal sources and include butter, milk fat, and the fat in meats. Two vegetable oils—coconut and palm kernel oils—are also highly saturated.

Unsaturated fatty acids do not have all the hydrogen atoms they can carry. If one pair of hydrogen atoms is missing, the fatty acids are called monounsaturated (olive, peanut, and canola oils are largely mono-unsaturated). If two pairs or more of hydrogen atoms are missing, the fatty acids are called polyunsaturated (corn, safflower, and sesame oils are primarily polyunsaturated). Plants and fish are important sources of un-saturated fats. These fats generally are liquid at room temperature.