Eating Fat to Get Thin?

Once upon a time, weight and health were not talked about in the same breath—or even the same drag of a cigarette. In fact, smoking—the mother of all bad health habits—was once thought of as a good way to keep weight down. 

In 1928 the American Tobacco Company launched an ad campaign in which attractive, slender women smoked Lucky Strikes. “Reach for a Lucky instead of a sweet,” advised one. “Light a Lucky and you’ll never miss the sweets that made you fat,” claimed another. Certainly even today many of us diet less out of concern for our health than to look like the emaciated fashion models in magazine ads (and, alas, fashion models still smoke to stay thin).

But more and more people are trying to lose weight to improve their cardiovascular health. The increased interest in weight issues among doctors and medical researchers over the past few years has been inspired primarily by the goal of preventing heart disease.

Because of the current emphasis on weight and its relation to heart disease (as well as diabetes and other conditions) the message overweight people have received about what they should eat has changed. Years ago it was thought that a calorie was a calorie and the idea was to eat fewer of them. Cutting back on fats was considered a good weight loss strategy since fat is more calorie dense (9 cal/gram) than carbohydrates and protein (both 4 cal/gram).

Overall calorie reduction – controlling portion size—is still essential to losing weight, but fat is not the villain it once was. For one thing, because fat is so rich in calories, we have evolved to find it tasty and satisfying and so it is difficult to stay on any diet in which fat is severely restricted. Second, certain fats are actually good for you.

Studies in the 1950s showed that countries where people ate a lot of saturated fat — the sort of fat in meat and dairy products — were more likely to have higher heart disease rates. Because saturated fat got a bad name, all fat did.

But the connection between overall fat intake and bad health outcomes turns out to be pretty tenuous. Neither of the two large epidemiological studies based at Harvard, the Nurses’ Health Study and the Health Professionals Follow-up Study, has found a link between the overall percentage of calories from fat in a diet and three of our biggest health woes: cancer, heart disease, and weight gain. The verdict has been the same from plenty of other large studies.

The studies comparing countries done in the 1950s weren’t wrong about saturated fat being bad for the heart. Replace carbohydrates with saturated fat, and your “bad” LDL cholesterol levels will go up. So will your “good” HDL levels, although not enough to cancel out the LDL increase.

The different types of fat

But if you replace those same carbohydrates with unsaturated fat found primarily in vegetable oils, you get the best of both cholesterol worlds: a decrease in LDL and an increase in HDL. Harvard researchers have estimated that if we were to replace a small amount of the carbohydrates we eat (the equivalent of 5% of our total calorie intake) with polyunsaturated fat, we’d lower our risk of developing heart disease by 30% to 40%.

But, as usual, it’s not quite so simple. Most of the saturated fat in our diets comes in one of four varieties: lauric acid, myristic acid, palmitic acid, or stearic acid. Their effect on LDL cholesterol varies, so among the saturated fats, there are degrees of bad. Stearic acid seems to be the least bad because it’s rather quickly converted into a healthful monounsaturated fat and doesn’t increase LDL levels very much, if at all. That’s good news for steak lovers: Half of the saturated fat in beef is stearic acid. Chocolate, already enjoying health accolades because of its blood pressure–lowering effects, looks even better when you consider that a third of the fat in cocoa butter is stearic acid.

Some trans fat occurs naturally in meat and dairy foods but most is artificial. Trans fat is produced by partially hydrogenating — that is, adding hydrogen atoms to — vegetable oils. Starting in the early 1990s, experiments showed that trans fat raised LDL levels like saturated fat and lowered HDL. It’s now seen as the really bad fat. Beyond its effect on cholesterol, trans fat seems to make platelets “stickier” (making blood clots more likely), stir up inflammation, and promote the production of extra-small LDL particles that are especially damaging to arteries. Studies have linked high intake of trans fat to diabetes, dementia, gallstones, heart disease, and infertility.

In 2006 the FDA started requiring food manufacturers to include trans fat in nutrition labeling. Because of the label requirement — and bans like those in New York City and elsewhere — many food manufacturers and restaurants have stopped using trans fat.

The bottom line

Calories still count, but increasing the percentage of fat--up to 40% of total calories— in your diet and decreasing carbohydrates may help curb overeating and benefit your cholesterol profile. The fats should be mostly mono- and polyunsaturated (for example, olive oil and canola oil), occasionally saturated (about the equivalent of a scoop of ice cream or a small cheeseburger) and never, if possible, trans. Dr. Walter Willett, chair of the Harvard School of Public Health’s nutrition department, even advocates violating an old dieting taboo of leaving the skin on when cooking chicken.

But don’t smoke Luckies—or any other brand.

Dr. Suzanne Koven practices internal medicine with a special interest in weight issues at Massachusetts General Hospital in Boston, and teaches at Harvard Medical School.

Eat, Drink, and Be Healthy
Millions of Americans concerned about healthy eating take their cues from the U.S. Department of Agriculture's Food Guide Pyramid. But according to renowned Harvard nutrition researcher Dr. Walter C. Willett, "That's a shame, because the USDA Pyramid is wrong…Indeed, it actually steers you away from foods that can improve your long-term health."

Dr. Willett’s national bestseller Eat, Drink, and Be Healthy serves as an alternative—and antidote—to the flawed new USDA Pyramid. The book explains how proper nutrition contributes to better health and longer life, and features a full range of recipes to help get you started.

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