David Katz, M.D.
I have a good -- or, depending on your appetite for large volumes of email, truly bad -- vantage point from which to observe both genuine and illusory controversies in nutrition. I am on a long list of list-servs and receive just about all the diet news that's fit to email.
Over recent months, a disproportionate volume of this traffic has been devoted to the exoneration, and at times, it seems, the canonization, of saturated fat.
In my view, this is one of the illusory nutrition controversies. Because the answers being espoused with ever greater passion and conviction are in response to the wrong question. The question being asked, it seems, is: Is saturated fat truly harmful? The right question is: Is all saturated fat created equal?
It is not. Saturated fat is not a compound, but a class of compounds. And we have long had strong indications that the class is home to both baby and bath water.
Before specifying the baby/bath water distinction and reaching actionable conclusions based on it, let's review the relevant history, for the usual reasons. The history of nutritional hyperbole is riddled with folly we would be well advised to learn from -- and avoid repeating.
In the beginning, dietary fat was all good. I do mean the beginning of our species, or as a recent proxy for it, the Stone Age. The best informed guesses of paleoanthropologists all point to the routine consumption by our many-times-over-great-grandparents of all the organ meats and bone marrow into which they could sink their teeth.
Why? There are, and have always been, only three macronutrient classes: fat, protein and carbohydrate. Carbohydrate provides four kcal per gram. Protein provides the same, or arguably, a bit less. Fat provides nine.
So for every gram of fat found and consumed, the caloric reward was more than twice that of the only alternatives. Since throughout most of human history, calories were relatively scarce and hard to get, a double dose was a true survival advantage. Survival imperatives, hard-wired into the Homo sapien hypothalamus, account for a prevailing penchant for dietary fat.
Why organ meats and bone marrow? Because fat was scarce just about every place else. There was some in nuts and seeds, and a bit in eggs. We may think of meat as a good source, but that's because the meat we eat today is the marbled muscle of domesticated animals, not the sinewy stuff of their wild forebears.
Turning again to the work of paleoanthropologists, they tell us that the meat we have eaten throughout most of our history was nothing like the meat we often eat today. For instance, beef from a modern, grain-fed steer may contain as much as 35 percent of its calories in fat, and much of that fat is saturated. In contrast, the flesh of antelope -- thought to be far more like the meat on which our species used to cut its teeth -- contains only about 7 percent of its calories in fat, almost all of which is unsaturated. And some of that fat is even omega-3.
While we tend now to refer to omega-3 oils as "fish oil," that's only because we have domesticated them out of other animals. Ungulates grazing on a diversity of wild grasses take in some alpha linolenic acid, and just like fish that get the same from algae and other sources, turn it into DHA and EPA. Modern fish-farming practices do at times, by the way, threaten a reduction or even elimination, of fish oil from fish. We are what we feed what we eat ...
But back to the Stone Age. Dietary fat was at a premium and highly valued. It was hard to get, rich in calories and an excess was not a threat -- nor even an option. Meat was lean, and until just 12,000 years ago at most, the only dairy that figured into the human diet was breast milk.
For quite a long time after the beginning, dietary fat stayed good. Right up to the pre-modern era, in fact, butter and cream were available to the affluent only, elusive for everyone else. Fat, when scarce, was a good thing -- just like calories.
But then like so much else in the modern era, dietary fat became mired in the perils of excess. Affluence and high-tech farming techniques converged to make access to fat easy and inexpensive for all. Then came ever more fried food, fast food and oil-containing processed foods. And then along came Ancel Keys, who looked out at all this and concluded that it was bad.
Keys, a researcher looking at cardiovascular disease in the 1950s, wasn't the only one with concerns about an excess of dietary fat, but he was among the earliest and most prominent to make his concerns public, most famously in the 7 Countries Study. Keys' work was then corroborated byWilliam Castelli and the Framingham Study, and fat became public health enemy #1.
As advice about restricting dietary fat proliferated, so did obesity and diabetes. But this had nothing to do with cutting fat, because we never actually did so! Data from the NHANES trials show we just diluted fat as a percent of total calories by eating ever more questionable carbohydrates! While a return to more plant-based eating might well have yielded the public health benefits the anti-fat faction was seeking, our collective turn to Snackwell cookies certainly did not!
And so along came Atkins, to tell us that fat had never been the problem in the first place -- the problem was carbohydrate. Atkins, of course, went further, suggesting that all fat was fine, and the more the better. The image with which his rise to stratospheric fame is most indelibly associated is a fatty pork chop adorned with a large pat of butter.
But, of course, Atkins ignored the fact that everything from lentils to lollipops is made of carbohydrate -- and that both salmon and salami are fatty, but hardly the same. He turned a blind eye on studies suggesting harms of saturated fat. His advice, for the health of people and planet, was seriously misguided.
At this point, one might argue that things began to improve. We started to recognize and acknowledge that some fats were beneficial, prominent among them monounsaturated fat and omega-3 fat; and some clearly harmful, notably trans fat and -- it seemed -- saturated fat. We started to see some attention to the fact that not all carbohydrate is created equal, either.
But we now find ourselves on the brink of more folly, as our penchant for all-or-none, active ingredient, silver-bullet scenarios wins out over vast experience with truth in shades of gray.
This is where the effort to exonerate saturated fat resides. We do, indeed, have evidence that saturated fat is not, and never was, our lone dietary peril. Excesses of calories, sugar, refined starch, sodium and trans fats -- among others -- share in that indictment.
But more importantly, we have evidence that not all saturated fat is created equal.
Stearic acid is a long saturated fat molecule and seems to exert no harmful effects. It is one of the fats found in meat and the predominant saturated fat found in dark chocolate. The 2010 Dietary Guidelines Advisory Committee very reasonably recommended that when we speak of restricting saturated fat intake, stearic acid need not be included.
There is less, but increasing evidence that lauric acid -- a very short saturated fat molecule -- may also be innocuous. It is the kind of saturated fat that predominates in coconut oil -- and the reason why the jury is still out on the health effects of its use.
I consider the evidence strong that palmitic and myristic acids, two of the commonly consumed saturated fats, are, indeed, potentially harmful, contributing to inflammation, elevated lipids, atherogenesis and vascular disease.
Note that even the exonerated SFAs appear to be harmless, rather than health-promoting per se. Nowhere in any of the evolving science is there a basis for the active promotion of saturated fat intake, which I am nonetheless hearing from certain quarters.
Now for three key points before we cross the finish line. First, we have innumerable studies showing that saturated fats -- notably palmitic and myristic acids which are found in dairy, meat and many processed foods -- can increase blood lipids and contribute to inflammation. While it's true that such fats may tend to raise HDL along with LDL, recent research raises questions about whether that's the benefit it appeared to be. And while it's also true that an excess of omega-6 polyunsaturated fats, and/or a deficiency of omega-3s can contribute to inflammation, that doesn't mean that saturated fats don't! It also seems likely that harms of saturated fat are very much compounded by the company they keep. Processed meat, for instance, is more clearly linked to bad health outcomes than just plain beef or pork.
Second, all oils are a mix of fatty acid types. While we think of olive oil as monounsaturated, it in fact contains monounsaturated, polyunsaturated and saturated fatty acids. Oleic acid, a monounsaturate, merely predominates. Since oils and foods contain a mix of fatty acids, we are almost never making pure comparisons of one type of fat to another, and for this reason, we might expect to see some overlap in health effects. Consider that if olive oil is good for health, there is a bit of saturated fat caught up in that conclusion. In the real world, "all good" vs. "all bad" is reliably more about salesmanship than data.
Third, and most important, we have very compelling evidence regarding the kinds of foods and diets that are associated with reduced risk of premature death and chronic disease -- and they are not diets high in saturated fat! The Lyon Diet Heart Study compared a Mediterranean-style diet rich in monounsaturated fats to a "typical French" diet much richer in saturated fat among people who had had a first heart attack. The rate of second heart attack was 70 percent lower among those on the Mediterranean diet! So much for the French paradox. The same results have been achieved on a plant-based diet, very low in total fat. No such results have ever been seen with any diet high in saturated fat.
Dietary fat was never all good or all bad; carbohydrate was never all good or all bad; and saturated fat is not now all good after having formerly been all bad. It depends on the specifics, which in turn depend on the foods you choose.
Choose wisely -- foods close to nature, mostly plants -- and you will avoid a host of ills, from the wrong kinds of fat, to excesses of sugar, salt, starch and calories. By choosing wholesome foods, you construct a wholesome diet -- with a good chance of adding both years to your life and life to your years. Vegetables, fruits, whole grains, walnuts, almonds, lentils, beans, seeds, olives, avocados and fish are all among the foods most decisively recommended for health promotion and all are low in saturated fat. That is by no means their only virtue, but it is among them.
While the science has moved incrementally into the realm of subtleties, we have remained mired in pop-culture fickleness about nutrition. But look around, and you will see what a fat lot of good it has done us to fall in and out of love with entire macronutrient classes!
Shifting that silliness to sub-classes, such as saturated fat, will do us no more good -- so let's not. Instead, let's learn from the follies of nutritional history and avoid repeating them.
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