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David Katz: The truth about saturated fat

A Mediterranean-style diet low in saturated fat is associated with reduced risk of disease and premature death. Photo/Getty Images

The fad for saturated fats is another example of our fickle approach to nutrition, writes researcher David Katz. Instead of focusing on food sub-classes, a balanced, plant-based diet holds the key.

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% 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% of its calories in fat, almost all of which is unsaturated. And some of that fat is even omega-3.

Back in 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 in the human diet was breast milk.

For quite a long time after the beginning of our species, dietary fat stayed good. Right up to the pre-modern era, in fact, butter and cream were available to the affluent only. 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.

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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, was among the first, and quite possibly the first, to consider that it might relate to diet and lifestyle, and not just be an inevitable consequence of ageing. Although his initial observations suggested a possible association between total dietary fat and heart disease, his own, famous, seven-countries study convinced him that association was limited to saturated fat.

Despite the voluminous commentary indicting Keys for America’s misguided foray into poorly conceived, low-fat eating, his actual position did not figure in that boondoggle. Keys advocated particularly for limiting saturated fat rather than total fat, and personally favoured a Mediterranean diet. His position was translated with fidelity into public health programming in North Karelia, Finland, and, there, was associated with rather stunning health improvements. In the US, when Keys’ work was corroborated by William Castelli and the Framingham Study, dietary fat – without much nuanced attention to variety – became public health enemy No 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! We just diluted fat as a percentage of total calories by eating ever more questionable carbohydrates. Thus, the health trajectories of North Karelia and North America parted ways decisively.

Then along came Dr Robert Atkins to tell us that fat had never been the problem in the first place: the problem was carbohydrates. Atkins, of course, went further, suggesting that all fat was fine, and the more the better.

Not all fat is equal

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 carbohydrates and that both salmon and salami are fatty, but hardly the same. He turned a blind eye to studies suggesting harms of saturated fat. His advice, for the health of people and planet, was, in my view then and now, seriously misguided. We have moved on since, and now do seem to recognise that all dietary fat is not created equal, and that kind and source matter. But our “all or nothing” mentality still tends to take over all too readily.

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 fundamentally, not all saturated fat is created equal. Saturated fat is not a compound, but a class of compounds, with variable properties. 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, although that advice did not make it into the official dietary guidelines.

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. Nowhere in any of the evolving science is there a basis for the active promotion of saturated-fat intake, which we nonetheless hear from certain quarters. I have searched for evidence that health benefits can result from the wilful addition of saturated-fat sources to the diet, and have not found anything convincing. That may be contrasted with strong evidence for vegetables, fruits, whole grains, beans, legumes, nuts, seeds and seafood, some of which is rich in unsaturated fat, none of which is concentrated in saturated fat.

We have innumerable studies showing that saturated fats, which are found in dairy, meat and many processed foods, can increase blood lipids and contribute to inflammation. Although 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 though 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 do not. It also seems likely that the 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, and there is much more nutritionally awry with processed meat than its saturated-fat content.

David Katz.

Misguided and misleading

Saturated fat from its customary sources (meat and dairy) has not earned the advocacy it now enjoys. The prominent studies many claim showed benefits of saturated fat showed no such thing. Two widely cited meta-analyses basically showed that across a realistic range of saturated fat in the diet, heart-disease rates were rather high and fairly constant.

What this really suggests is that diets higher or lower in saturated fat found different ways to be bad, a conclusion verified by an observational cohort study at Harvard. When saturated-fat calories are replaced with whole grains, or unsaturated fats from nuts and seeds, health improves. When those calories are replaced by sugar and refined starches, health outcomes are bad both times.

The misguided and misleading clamour about saturated fat being “good” for us resulted in the unusual publication by the American Heart Association of a presidential advisory in June 2017. The multidisciplinary panel of authors weighed saturated fats in every relevant way, measured them with every pertinent metric, and found them wanting.

There are no saturated fatty acids shown to be better than “harmless at best” and those we consume most often and abundantly in fatty meats, processed meats, fast foods, dairy and processed dairy products are decisively worse than that. They are bad for us.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% 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.

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.

Make wise choices

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, but some are quite high in total fat. These are by no means their only virtues, but they are 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 particular varieties of 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 by actually eating well this time.

From The Truth About Food: Why Pandas Eat Bamboo and People Get Bamboozled, by David Katz. Available through Amazon.com in paperback and e-book. Katz is the founding director of Yale University’s Yale-Griffin Prevention Research Centre and founder/president of the True Health Initiative, a non-profit organisation set up to promote a healthy, sustainable diet and lifestyle.

This article was first published in the February 9, 2019 issue of the New Zealand Listener.