It's just not fair: Fat got a bad rap decades ago because scientists assumed, based on the misinterpretation of a couple of large studies, that eating foods containing fat would lead directly to obesity and heart disease. Fatty foods were made out to be our sole dietary vice, responsible for raising our cholesterol levels, clogging our arteries, and causing us to get, well, fat.
And that made a kind of intuitive sense—why wouldn't the fat you consume wind up as the fat you see on your butt and thighs? But "the low-fat diet backfired," said Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health. "America's obesity epidemic skyrocketed even while our fat intake went down." So experts are getting off the "fat is evil" bandwagon these days—and we should, too.
The upside of eating fat
Like carbohydrates and protein, fat is an essential nutrient. This means that your body requires it for key functions, such as absorbing the fat-soluble vitamins A, D, E, and K. "Fat is also an important energy source and is vital for keeping your skin and hair healthy and smooth," said Bonnie Taub-Dix, author of Read It Before You Eat It.
Even more surprising: Research is revealing that eating the right fats can actually lower your risk of diabetes, heart disease, and obesity, and improve your cholesterol levels. That's because all fats are not created equal, Hu pointed out.
It's not the total amount of fat in your diet that affects how much you weigh or whether you're at risk for heart disease, according to rigorous studies from the past decade. What matters is the type of fats you choose (and, when it comes to dropping pounds, the total number of calories you eat). Here's a breakdown.
Monounsaturated fatty acids (MUFAs)
Found in plant foods like nuts, avocados, olive oil, and canola oil, and in poultry
MUFAs can actually lower cholesterol levels, and, in doing so, your risk of heart disease. In fact, a Journal of the American Medical Association study showed that replacing a carb-rich diet with one high in monounsaturated fats can do both, and reduce blood pressure, too.
Polyunsaturated fatty acids (PUFAs)
Found in fatty fish such as salmon and mackerel, and corn and soybean oils
Like MUFAs, PUFAs have been shown to improve cholesterol levels and reduce heart disease risk. One type is the omega-3 fatty acid, which is plentiful in some kinds of fish—not to be confused with omega-6 fatty acids, found in meats, corn oil, and soybean oil. Some research finds that Americans eat about 20 times more omega-6 than omega-3; we should be aiming to get closer to four times as much. To do so, Hu said, sub in fish for meat when you can.
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Found in meat and dairy products such as cheese, butter, and milk
We've been warned for decades to eat less saturated fat—after all, it raises "bad" (LDL) cholesterol levels, and thus, it was assumed, ups your risk of heart attack and stroke. Lately, though, research has begun to vindicate it.
For instance, a 2010 American Journal of Clinical Nutrition review of 21 studies was unable to find a link between saturated fat consumption and heart disease or stroke. Some types have been entirely exonerated: "Stearic acid, found in dark chocolate, is clearly non-harmful," said Dr. David L. Katz, director of the Yale University Prevention Research Center. The same may be true of lauric acid, a type of saturated fat abundant in coconut oil, but there's not enough evidence to say for sure, Katz said.
While some experts, like Katz, say there's no downside to cutting out saturated fats, others believe keeping them in the mix helps us avoid getting too many bad-for-you refined carbohydrates instead. Bottom line: You don't need to ban them. Just make sure most of your fat intake is unsaturated, eat red meat only once or twice a week, and use olive oil instead of butter when possible.
Found in some fried foods, shortening, and packaged snacks like crackers and desserts
Trans fat gained notoriety several years ago when one state and a handful of cities banned the artificial kind—found in partially hydrogenated vegetable oil—from restaurants. (Trans fats also occur naturally in small amounts in some foods.)
Research has found that artificial trans fats raise LDL cholesterol and lower HDL cholesterol—and a high LDL/low HDL combination can increase your risk of heart attack and stroke. Still, partially hydrogenated oil remains a fairly common ingredient in processed foods, in part because adding hydrogen to vegetable oil gives it a longer shelf life.
Experts agree that you should cut out trans fat altogether—and thankfully, that's not so hard to do. "Limit your intake of processed foods, commercial snacks, and fast food, and you'll avoid trans fat," Katz said.
Don't assume you're in the clear if your packaged snack says "0 trans fats" on the label. "Food manufacturers are allowed to put '0 trans fats' in the nutritional information if the item has up to 0.5 grams of trans fat per serving," said Taub-Dix. "Look at the ingredient list: If you see the word 'hydrogenated,' then the food has trans fat and you should skip it."
Eat fat, lose weight
We know what you're thinking: How do you control calories if you're downing chocolate, olive oil, and nuts? After all, fat packs 9 calories per gram, compared to 4 cals per gram of carbs or protein. Well, for one thing, when you eat a food that contains some fat, you're likely to feel satisfied faster than when eating something fat free. That means you'll consume less of it and will likely be less tempted to snack later on.
Some studies have also indicated that certain fats work to help you stay slim: For instance, Harvard researchers found that people who ate nuts regularly gained less weight over a four-year period than those who didn't. Plus, foods labeled "reduced fat" or "fat free" can actually contain more calories than their full-fat counterparts, because the fat has been replaced with sugar, starch, and other fillers with little to no nutritional value to add back flavor.
As for dairy, we've all heard that drinking milk (and eating yogurt) can boost bone health and even lower blood pressure and promote weight loss. If you're getting the multiple servings of milk you should each day, consider making some of it low fat to keep saturated fat and calories down. When it comes to cheese, Hu recommended indulging in the full-fat stuff occasionally; it has more flavor than low-fat cheese, so a little goes a long way.
So how much "good" fat you should get? The American Heart Association recommends that unsaturated fats make up 18 to 28 percent of the calories in our diets, with no more than 7 percent of our daily calories coming from saturated fat. But here's an easier rule of thumb: "I just make sure that the fats I eat come from healthy food sources—like vegetable oils, fish, legumes, nuts, and other plant-based foods," said Hu. "If you do that, then there's no need to count."