Dietary Fat: the Good, the Bad and the Ugly

For your best health, get the right balance of real foods

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There was a time, not long ago, when all dietary fat was bad for our health. It was not truly bad, of course, but we talked ourselves into believing it was. How we responded behaviorally to that belief never made any sense, but that's a topic for other columns, past and future. For now, it suffices to note that we labeled all fat bad, and we were wrong.

Eat + Run -- David Katz
David Katz
One would think, and certainly hope, that having engendered years of public policy and massive shifts in the food supply and prevailing behavior with a misguided boondoggle, we would be extremely cautious about doing it again. But not so! Repeating the follies of dietary history has become something of an honored vocation, if not a national pastime.

Even in the aftermath of having been wrong about dietary fat in general, competing views about specific members of that large and diverse nutrient class are asserted with undiminished conviction.

The case has been made by one research group, for example, that dietary cholesterol (and therefore eggs) is as harmful as tobacco. This would be astounding, if true, because tobacco has long been recognized as an even more important cause of disease and premature death than poor diet. So, in other words, if this assertion about cholesterol were true, it would leave almost no room for any other aspect of diet to account for any harm, because all dietary harm would be accounted for already. Figuring this out is not rocket science.

The assertion about cholesterol is almost certainly wrong for this reason alone. But there are others. The study was led by an ardent proponent of vegan eating, and cholesterol, of course, is only found in animal foods. The study methods were extremely vulnerable to bias. And, there is a large body of evidence that, in the aggregate, all but eggsonerates the egg. Let's move on.

[See Cholesterol Management]

When we began to recognize that all fat wasn't evil, we needed a new villain. We chose saturated fat, and not unreasonably so. Around the world, diets high in saturated fats are associated with high rates of heart disease. But, of course, diets that derive lots of their calories (and, consequently, saturated fat) from meats, dairy, fried foods and so on, must derive less of their calories from alternatives—such as vegetables, fruits, nuts, seeds, beans, lentils and so on.

One of the perennial blind spots in nutrition epidemiology is that eating more of A either just means eating more altogether, which brings ills of its own—or eating less of B. And thus, the harms of A may be partly explained by losing the benefits of B. In our perennial rush to judgment, such subtleties are routinely trampled.

Simple reflections of this sort begin to suggest how we might have exaggerated the harms of saturated fat. Switching saturated fat to starch or sugar or trans fat could well be trading sideways, or even down.

But that would not necessarily fully absolve saturated fat, as many voices are now suggesting with unfounded zeal. The evidence we have about saturated fat is not limited to population studies. It includes mechanistic studies showing that certain prevalent saturated fatty acids found in dairy and meat—palmitic acid and myristic acid—induce inflammation and atherogenesis (the process that gums up our arteries).

[See Dr. Weil's Anti-Inflammatory Diet]

But the same kind of evidence indicates that other saturated fatty acids such as stearic acid, found prominently in dark chocolate but also in meat, and lauric acid, found in coconut, may be innocuous. All saturated fat is not created equal. We once applied this mistaken "can't differentiate baby from bath water" appraisal to all dietary fat. Instead of learning from it, we now apply the same broken method to classes of fat.

And that now extends to polyunsaturated fat of the omega-6 class. Among my more adamant and persistent of my correspondents are those trying to convince me that what we once thought true of saturated fat—namely, that it's bad—is actually true of omega-6 fat. I am told several times a week that it's this bad polyunsaturated fat that is the REAL cause of heart disease, cancer and our various other prevailing woes. Such thinking has even been distorted to the point of recommending bacon over tilapia.

[See Best Heart-Healthy Diets]

But this is just the same old misguided nonsense, tossed in a new direction. Omega-6 polyunsaturated fat is, in fact, essential for normal human function. Along with polyunsaturated fat of the omega-3 class, these groups make up the "essential fatty acids."

It's true that omega-6s induce inflammation. Omega-3s, in contrast, tend to be anti-inflammatory. Neither is good nor bad. They are nutritional yin and yang. We need them in balance, and both in balance with other nutrients.

Paleoanthropologists tell us that our native intake of omega-6 and omega-3 was in a ratio of between 1-to-1 and 4-to-1. In modern diets, we eat 11 to 20 times as much omega-6 as omega-3. Is that a problem? Yes. Does it make omega-6 bad? No. Being out of balance is bad.

This situation can likely be improved by eating more omega-3, and/or eating less omega-6, along with eating more monounsaturated fat. But we have no evidence that it would be improved by eating more saturated fat, as many now argue based on next to nothing.

For those preoccupied with omega-6s, cutting them is the one true answer. For those preoccupied with saturated fat or cholesterol, those remain the real problems. Those focused on omega-3s argue that increasing those should be the priority.

Even as factions skirmish over competing views of dietary fats, others see a basis for battle on a different war front altogether. Some contend that the only thing meaningfully wrong with our diets is the sugar, while others argue it's the dairy, and still others, the gluten. Others still argue it's all about carbs, or animal foods, or animal protein, or glycemic load, or lecithin. Some argue it is salt, others calories—while others still seek to exonerate both salt and calories entirely. And everyone, it seems, is sure they're right.

[See Use and Abuse of the Glycemic Index]

For the most part, those vindicating this or vilifying that are smart and well-intentioned people. The only thing I seem to have latched hold of that they have missed is this: If any one of them is right, then all the others are wrong.

Let that sink in. All of the world's major (and probably minor) religions count among their congregations devout, pious people who believe their group knows the true nature and intentions of the almighty. If any one of those groups is right, then all of the others are wrong. And, so, alas for the equally pious, devout people who happen to be seeking the wrong truth in the wrong temple!

In the parable of the Blind Men and the Elephant, John Godfrey Saxe allows for all of the competing religious views to be a little right, but mostly wrong. What's mostly wrong, of course, is that they don't allow for the possibility that others are at least as right.

For what it's worth, I have the same concerns about privileged claims to absolute truth in the realm of religion. Look at the hatred and troubles competing versions of absolute truth bring us. But religion is not my professional realm, and I will let others wrestle with theology. Epidemiology keeps me plenty busy—particularly as the same problem overtakes us.

It is a mistake—a grave mistake—to infuse the imperfections of an ever-evolving science with religious zeal. Let me state the obvious: No one has claim to absolute nutrition truth, or complete knowledge. No one. And be reminded that the wise and thoughtful and cautious allow for doubt, while hucksters and the deluded have a constant monopoly on certainty.

Renouncing claim to absolute knowledge of every tree does not leave us lost in the woods. We know what diets are associated with the best health outcomes. What do these diets tell us? Is it all fat, or saturated fat? Fructose or carbs? Cholesterol or omega-6s?

None of the above. The problem is imbalance. Bad combinations of questionable foods.

We know that a diet rich in vegetables and fruits; beans and legumes; nuts and seeds; whole, unrefined grains; fish; eggs; with or without seafood, lean meats, and dairy—and variations on such a theme—promotes health. Such a diet is relatively low in saturated fat, but not fixated on it. Such a diet is virtually devoid of trans fat, as that is found preferentially in processed junk.

[See Plant-Based Diets: A Primer]

Such a diet provides a balance of omega-6s (from nuts, seeds, grains and oils) and omega-3s (from nuts, seeds, fish and seafood). It provides monounsaturated oil from nuts, seeds, olives and avocado. It provides little added sugar, because most foods are close to nature. It provides for moderate sodium intake, because most sodium is added during food processing.

Focus on the forest of foods, in other words, and the trees will sort themselves out. Climb a tree, barking mad—and enjoy the show as the forest burns down.

The best way to choose the best fats is to choose the best foods in the right proportions. If you are expecting to find your way to better eating and health by selecting a single villain or savior, well—fat chance.

Some dietary fats are good for us. Balance and proportion are good for us. Some dietary fats are bad for us. Deficiencies, excesses and imbalances are bad for us.

Sweeping generalizations, exaggerated claims and a silly sequence of vindications and vilifications are downright ugly. It's far past time to chew the fat accordingly, and spit out what history abundantly proves is indigestible nonsense.

[See Recipe for Health]

Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.

David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.