Last updated: Aug 05, 2014
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Is dietary fat good or bad for us? Is saturated fat harmful to the heart? There's no bite-size answer to either of these questions. Back when we believed that all dietary fat was bad, we were wrong. But when we adopt the opposite view—that all dietary fat has been unfairly maligned and is actually beneficial—we are wrong again.


To understand how fat became so controversial, we need a quick history lesson. In the mid-20th century, the American physiologist Ancel Keys, PhD, compared health outcomes among countries around the world and discovered there were higher rates of heart disease in societies that ate a lot of meat and dairy and much lower rates in societies with mostly plant-based diets. His advice in a nutshell: Eat less of the higher-fat foods that predominated in America in the 1950s—including hamburgers and hot dogs, butter and ice cream—and eat more naturally low-fat foods, emphasizing vegetables and fruits.

RELATED: A Guide to Good and Bad Fats

What happens when you make this change? In 1990, my friend Dean Ornish, MD, showed in dramatic fashion that a very low-fat, mostly plant-based diet can shrink the plaque in coronary arteries, actually reversing heart disease. And it could even modify gene expression and slow, stop and reverse the progression of certain cancers.

Cutting fat, adding calories
Unfortunately, Americans never did anything remotely like what these scientists recommended. We didn't include more produce in our diet. In fact, we never even trimmed our fat intake, according to national dietary data. Instead, we simply added more low-fat processed foods, high in refined starch and added sugar. As a result, we did reduce our fat intake as a percentage of total calories—but only because our total calories went up, not because our fat intake went down.

Of course, this didn't improve our health. Rates of obesity and diabetes rose, and "cutting fat" was blamed. The notion that Ancel Keys was profoundly wrong has been evolving into New Age gospel since the Atkins Diet era.

RELATED: 22 Worst Foods for Trans Fat

Keys' message was imperfect. For example, we now better understand that not all fatty foods are bad for us: Walnuts, almonds, wild salmon and avocados may be high in dietary fat, but they are also superfoods. Overall, though, if we had followed Keys' advice—to eat foods naturally lower in fat—our health as a nation would almost certainly have improved and our weight would have declined.

Making sense of the controversy
Yet now the "all fat is good" message is gathering strength. The latest example: the wildly excessive response to a meta-analysis (a pooling of previous studies) published in the Annals of Internal Medicine in March. The research team looked at people's intake of specific fatty acid categories (saturated, monounsaturated, polyunsaturated and trans) and subtypes within those categories (such as omega-3 and omega-6 polyunsaturates) and how that corresponded to coronary heart disease rates. The part that got the most attention: They found no appreciable difference in coronary heart disease rates between people who had the highest saturated fat intake and those who had the lowest.

Headlines blared, "Fat Is Good for You." But the fact is that around the world, diets heavy in saturated fats are associated with higher rates of heart disease. Other studies show that certain saturated fatty acids prevalent in dairy and meat—palmitic and myristic acids—induce inflammation, which is linked to atherogenesis (the process that gums up our arteries).

RELATED: 15 Recipes Low in Saturated Fat

To further confuse the issue, not all saturated fats are equal. Research suggests that other saturated fatty acids, such as stearic acid (found prominently in dark chocolate) and lauric acid (found in coconut oil), may be innocuous.

So why did that news-making study find no benefit from diets with less saturated fat? People don't simply stop eating saturated fat and leave a big hole in their diet. They make up for it by eating more of something else. The question this review never asked: What was that something else? Replacing saturated fat with starch or sugar could mean making your diet worse.



How to eat now
Time and time again, research has shown that the diets that promote health are rich in vegetables and fruits, beans and legumes, nuts and seeds and whole grains, with or without fish, eggs, seafood, lean meats and dairy (I recommend low-fat or nonfat).

RELATED: 50 Fattiest Foods in the States

This eating style is low in saturated fat (without having to fixate on it) and virtually devoid of unhealthy trans fat; it also gives a good balance of polyunsaturated and monounsaturated oils. And since most of the foods are close to nature, it contains little added sugar and moderate sodium.

RELATED: Simple Swaps to Cut 500 Calories

Bottom line: The secret to choosing the ideal fats is to pick better-for-you foods in the right proportions. It really is that simple.

Your Fat Decoder
Can't tell a PUFA from palm kernel oil? Check out our cheat sheet.

Trans fat is usually found in processed foods (packaged snacks and desserts), fried foods and shortening. It also occurs naturally in small amounts in some foods. You'll recognize it on the ingredients list under the name "partially hydrogenated vegetable oil." It's linked to higher LDL, or "bad," cholesterol levels and lower HDL, or "good," cholesterol levels.

Saturated fat is found mostly in foods that come from animals, like red meat, poultry and dairy products. It's also in some plant foods, like coconut oil and palm kernel oil. Certain types of saturated fat are worse for your health than others.

Polyunsaturated fatty acids (PUFAs) include omega-3 fatty acids (found in fatty fish like salmon and plant foods like walnuts and flaxseed) and omega-6 fatty acids (in vegetable oils like corn oil). They can help lower cholesterol and cut your risk of heart disease.

Monounsaturated fatty acids (MUFAs) are in plant foods like nuts, avocados and olive oil. They have been shown to lower LDL levels and reduce heart disease risk.