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'Good' Fat Better Than No Fat?


From packages on supermarket shelves that scream "fat free" to our nation's dietary guidelines, it's clear that fat is Public Enemy No. 1. And you've heard the message for so long that it's become a mantra: the less fat in your diet, the better.

But now a controversial study by Harvard researchers has thrown the nutrition community on its ear--and may likely change the way we eat. The new report, concluded after a 14-year study of some 80,000 female nurses, states that it's not how much fat a person eats, but rather the types of fat that are most important in determining heart health. "Total fat is not one entity. It's a composite," says Dr. Frank Hu, lead author of the study published recently in the New England Journal of Medicine. "Different types of fat have different effects."

Of course, we've known for years that certain types of fats are more healthful than others. For instance, saturated fat, found in meats and dairy products, has long been considered one of the main culprits in heart disease; monounsaturated fat, found abundantly in olive and canola oils, is actually protective against heart disease. The recommendation, however, was still to avoid fats whenever possible. What makes this study so groundbreaking is the finding that, for preventing heart disease, it's better to eat foods containing healthful fats than to choose foods with no fat at all.

This assertion is quite radical and has champions of low-fat eating up in arms, such as Dr. Dean Ornish, whose extremely low-fat diets are said to have helped reduce cardiac risk for people with severe heart disease. But there is further evidence to support it: A recent study published in the Journal of the American Medical Assn. showed that men on low-fat diets actually fared worse than those on moderate-fat diets, with the low-fat group's HDL ("good") cholesterol levels dropping and harmful triglyceride levels rising.

What's the problem with very low-fat diets? It's that we, in our efforts to lower fat intake, replace fat with carbohydrates--a twofold dilemma. First of all, while replacing fatty foods with carbohydrate-rich foods such as pasta, rice, potatoes and bread does lower total cholesterol, it also lowers HDL cholesterol levels, increasing heart-disease risk more than diets that replace saturated or trans fats with unsaturated fats.

Replacing fat with carbohydrates may also contribute to diabetes by increasing blood-insulin levels. But before you rush to your pantry to throw out all your starchy foods, consider this: Carbohydrates are not unhealthful and should make up 55% to 65% of your daily calories. It's only when people overload on them and drastically reduce their fat intake that this eating approach becomes a problem.


Call it a food revolution, if you will. Not only are we being told that we don't need to obsess about how much fat we eat as long as we eat the right fats, but we're also being told that replacing "bad" fat with "good" fat is more healthful than replacing it with carbohydrates. There is, however, one more piece to this puzzle that you'll need to know to make informed decisions at the supermarket: Which is worse, saturated fat or so-called trans fat?

Trans fats are made by taking fats we generally think of as healthful--poly- and monounsaturated vegetable oils--and converting them chemically so they become solid at room temperature. Because they cost little and resist spoiling, they're found in myriad processed foods such as white bread, cookies and crackers.

These "artificial" fats became increasingly popular in the late 1980s, when they seemed such a good replacement for highly saturated tropical oils in processed foods and fast-food fryers. This trade-off may have had major health consequences, though. While we eat only a small amount of trans fats (about 5% of our fat intake), they appear to pose a big problem: Trans fats act very much like saturated fats in increasing levels of LDL ("bad") cholesterol, but they also reduce levels of HDL (good) cholesterol and raise levels of triglycerides, a triple-whammy for the heart.

Actually, it seems that smaller amounts of trans fats are more harmful than larger amounts of saturated fat. Case in point: In the nurses' study, replacing a small amount of carbohydrates with saturated fat caused a 17% increase in coronary artery disease, whereas replacing the same amount of carbohydrate with trans fat caused a 93% increase.

"Increases in coronary heart disease rates in this country parallel the consumption of trans fats in the American diet," says Dr. Walter Willett, a study coauthor who has been concerned about the health effects of trans fats since the 1970s and who thinks these artificial fats should be eliminated from foods.

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