saturated fats

The Truth About Saturated Fat

The Truth About Saturated Fat

There is a booming cottage industry these days peddling the argument that saturated fat is suddenly good for us, with some fairly prominent health professionals involved. Unfortunately for those of you eagerly awaiting a license to eat unlimited quantities of pepperoni, the argument is invalid.

We could slog through a whole lot of scientific detail here, but it’s not necessary. The relevant literature has already been summarized for us in some rather famous, if not infamous, systematic reviews. The very purpose of systematic reviews, and their quantitative counterpart, meta-analysis, is to help establish conclusions based not just on any one study, but the overall weight of evidence. Systematic reviews and meta-analyses about saturated fat and health outcomes are readily available.

There are, in particular, two such reviews that turn up most often when the case is being made that we should all eat more meat and put butter in our coffee. The first dates from 2010; the second from 2014. They differ in many details, but they effectively address the same basic issue. Both examined the variation in heart disease across a range of saturated fat intakes (generally measured as a percent of total calories).

What did they find? Rates of heart disease were high, and almost exactly the same, at the high and low ends of the saturated fat intake range. The currently popular argument seems to be that rates of heart disease did not go down when saturated fat intake went down; and therefore, saturated fat must be good for us now.

This is absolute nonsense. We could use exactly the same data, and just the same « logic, » to argue that rates of heart disease did not go down when saturated fat intake went up; and therefore, saturated fat must be bad for us (still).

The simple fact is that neither of these assertions is valid. If heart disease rates don’t change across the range of saturated fat being examined, all it does is raise additional questions. How much variation is there in saturated fat intake in the first place? If there isn’t much, it’s no surprise that outcomes affected by saturated fat don’t vary much either (not much change in X leading to not much change in Y falls well short of a revelation). When saturated fat intake goes down, what is replacing it – and what is happening to the overall diet quality?

We have the answers to these questions, kept in the shadows impressively well by the peddlers of pepperoni and bacon. Since I have no charcuterie to sell you, I am happy to share them:

  • The range of saturated fat intake examined is pretty narrow. In the first meta-analysis, the top and bottom of the range often differed by only a few percentage points, and even the bottom of the range was above current recommendations. The later meta-analysis compared the top third of the population to the bottom third and, again, the difference was small.
  • To the extent saturated fat intake has gone down over time in the U.S. – and it hasn’t gone down much – it has mostly been replaced by sugar and refined carbohydrates.

A generally neglected consideration is that overall diet quality was comparably bad at the « extremes » of the rather narrow saturated fat range observed. That’s about what we would expect if the main alternatives to saturated fat from burgers, pizza and ice cream were refined carbohydrate and sugar from soda, cookies, fries and donuts.

The available evidence suggests exactly that. Data from both the U.S. Department of Agriculture and the Centers for Disease Control and Prevention suggest that animal fat intake in the U.S. has stayed fairly constant over recent decades, while sugar intake, refined carbohydrate intake and total calories have gone up.

The crucial question neither oft-cited meta-analysis answered is this: How does variation in saturated fat intake affect rates of heart disease when the alternatives to saturated fat calories are assessed? A 2015 paper provides the answer. In roughly 125,000 people over nearly 30 years, heart disease rates went from bad to even worse if trans fat replaced saturated fat, stayed the same when sugar and refined carbohydrates replaced saturated fat and declined significantly when saturated fat calories were replaced with either calories from whole grains or calories from unsaturated fats coming from nuts, seeds, olive oil, avocado, fish and seafood. A more recent study of comparable size and methods appended this: Rates of heart disease go up when more of total dietary fat is saturated, and go down as more of total dietary fat is unsaturated.

Shockingly at odds with the current case for saturated fat, what all of these data seem to indicate is just what both science and sense suggested all along: A diet made poor by an excess of saturated fat from the usual sources – think beef, processed meats, fast food and processed dairy – is almost exactly as bad for health outcomes as a diet made poor by an excess of sugar and refined carbohydrate from the usual sources. There is more than one way to eat badly – and we seem dedicated to exploring them all.

That’s tragic because the fundamentals of a genuinely healthful diet are clear, supported by vast and diverse evidence and a matter of global consensus. They translate into dietary patterns of wholesome foods in any of various sensible combinations that are inevitably low in added sugar, refined carbohydrate and saturated fat alike. Applied routinely, they could add years to lives, and life to years – and benefit the planet too.

It’s certainly true that saturated fat is not, and never was, the one and only thing wrong with our diets. It’s also true that not all saturated fats are created equal. But those are not the propositions that are being peddled so effectively. The premise that we must choose the one, true dietary scapegoat from either saturated fat or sugar is benighted nonsense.

The very science most often invoked to argue the case for more saturated fat actually shows it to be almost exactly on par with sugar. How ironic and absurd that of all things, the truth about saturated fat should be sugarcoated.

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