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Ending the Big, Fat Debate

The cap on dietary fat has, indeed, long outlived any utility it ever had. So, too, has a big, fat debate that has diverted us for far too long to nutrients, from the foods that would be a far more constructive, and healthy focus.
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Achieving a clear understanding of the health effects of dietary fats requires a challenging slog through a thick tangle of opinions. These days, it's rare to get through any given news cycle without contentions about dietary fat, expert and otherwise, coming at us from every quarter. The preoccupation, especially intense now, has a rather long lineage.

Call to Action: Let's End the Big Fat Debate

  • It is time to end the big, fat debate- by focusing less on nutrients, and more on foods.
  • Some of the most nutritious foods are extremely low in fat (e.g., broccoli, spinach, blueberries) and some, high (e.g., walnuts, almonds, flaxseeds, avocado, salmon). Some of the world's most nutritious diets contain little fat (e.g., most vegan diets), and some, rather a lot (e.g., most Mediterranean diets).
  • Focusing just on fat, or any other nutrient, does not lead reliably to a wholesome, health-promoting diet. Focusing instead on a dietary pattern of wholesome foods in sensible combinations does lead reliably to an appropriate balance of all nutrients.
  • Let's talk less about nutrients, and more about foods. If we get the foods right, the nutrients will take care of themselves!
  • Source: Katz DL, Meller S. Can we say what diet is best for health? Annu Rev Public Health. 2014;35:83-103

Ancel Keys began suggesting we should restrict our intake of dietary fat, saturated fat in particular, as far back as the 1940s. Other notables joined that chorus soon after. Robert Atkins first suggested we should liberalize our fat intake and cut carbohydrates instead in the 1970s, although his message made its greatest impact when reprised two decades later. Recent years have brought us point and counter-point about fat and other nutrients with increasing frequency, and apparent acrimony.

The better part of a decade and a half ago, we were told that everything we had heard about dietary fat might be a Big, Fat Lie. After a dozen years to chew on that, we received much the same memo last year, as if new, and told it should it all come as a Big, Fat Surprise. So it is the big fat debate has raged for decades, and all the while our population has generally gotten fatter, and sicker.

Is butter back, or isn't it? Should there be any cap at all on our intake of dietary fat, and if not, is more now better? Why the seemingly interminable Big, Fat Debate- and what really is the truth about dietary fat and our health?

Recent opinion pieces in both JAMA, and reiterated in the New York Times, ostensibly call for an end to the "ban" on a limited intake of total dietary fat. In doing so, the authors invoke the report of the 2015 Dietary Guidelines Advisory Committee, which does indeed relegate to the dustbin of dubious ideas the proposition that we should honor some specific cap for total fat. The DGAC report preferentially emphasizes the foods we should eat for better health, some of which, like nuts, are natively high in fat, and correspondingly deemphasizes nutrients, although they are, of course, addressed.

Inevitably, the attendant commentaries go mostly the other way, focusing primarily on fat, and secondarily on the foods delivering it. In the context of competing claims about dietary fat, considerable clamor, and general confusion, that focus is understandable. I favor the former approach, however- foods over nutrients. Either way, a cap on dietary fat intake has clearly outlived any utility it ever had.

That is not to say all dietary fats are good for us. Some, like the trans fats being expelled from the food supply by the FDA, are quite simply toxic. The proliferation of trans fat through the food supply, as replacement for highly saturated tropical oils, was intended to advance public health. We have long had evidence that the opposite was achieved; trans fat is clearly more potently inflammatory and atherogenic (i.e., contributes to the formation of atherosclerotic plaque in arteries) than any naturally occurring fat in our diets.

As for the saturated fat that prompted the trans fat boondoggle in the first place, it is neither as sinister as its most ardent detractors contend, nor as saintly as its New-Age apologists propose. Saturated fat represents a complex and diverse family of compounds of quite variable character. Some members are still convincingly linked to important adverse health effects, notably increased risk of cardiovascular disease. Others, notably stearic acid, have been rather robustly vindicated of any ill effects. Still others, like lauric acid predominant in coconut oil, remain the focus of unresolved scrutiny, with the jury leaning toward exoneration. In no case, however, has saturated fat been decisively linked to health benefit.

In the aggregate, then, the contentious discourse on saturated fat demonstrates the signature peril of unending debate, and its Newtonian cadence: for every argument, an equal and opposite counter-argument. Lost in the cacophony of such exchange is a temperate truth in the middle: not all saturated fat is created equal; not all saturated fats are harmful; none to date is convincingly beneficial. Much, predictably, depends on dietary context, and specific food choices.

Much the same is true, albeit in the opposite direction, of unsaturated oils. This family of compounds is even larger, and more diverse, encompassing both monounsaturated and polyunsaturated oils. The former, the predominant fat type in olive oil, is indelibly linked to the health-promoting Mediterranean diet, and has been identified among the "active ingredients" of that diet, responsible for its salutary effects.

The latter group, polyunsaturated fats, is home to the only fats we truly need: essential fatty acids. Those, in turn, come in several varieties, the best known referred to as omega-6 and omega-3 fats. Predictably, much noise has been made about both. The prevailing intake of omega-6 fat in modern diets tends toward excess, resulting in at times exaggerated claims of attendant harms. Intake of omega-3 fats tends toward deficiency, resulting in comparably exaggerated claims of benefit. The reality is that these fats exert favorable effects in a balance best achieved by a sensible diet of wholesome foods.

As with so much else about nutrition, the truth about fat is a bit more nuanced than the dumbed down, hyped up assertions that all too often prevail would suggest. There is no real evidence that any benefit results from restricting total dietary fat intake per se, but on the other hand, most real-world dietary patterns associated with good health outcomes fall within a rather temperate range of total dietary fat. Reducing our intake of saturated fat has not produced the health benefits expected, but this is almost certainly due more to what we started eating instead, and less because saturated fat was mischaracterized. Certain oils, and the foods in which they are native, are clearly health promoting. Certain fats, notably trans fat, are decisively harmful. There is good, bad, and ugly in the mix. Much as we seem to wish for black and white truths on the topic, there are shades of gray.

There are four principal reasons decades of debate about dietary fats have done more to undermine understanding than advance it:

1) We have routinely conflated baby and bathwater.

When adverse effects of certain high-fat diets were observed, we somehow listed toward a focus on cutting fats wholesale. The result, utterly benighted in retrospect, was to embrace low-fat foods no matter their composition, while banishing from our diets all high-fat foods, some of which, notably nuts, seeds, and fatty fish are clearly linked to health benefit.

2) We gave away the Keys to the kingdom.

Leaving aside the divergent opinions about the career and contributions of Ancel Keys, we may reliably accept that he never recommended Snackwell cookies. When Keys and others first recommended we reduce our intake of dietary fat, low-fat cookies and junk food had not yet been invented. They were, in fact, invented in response to the recommendation. The result was that a message born of epidemiology was coopted by Big Food, and converted into something never intended. We never replaced sausage with spinach; we started eating Snackwells with a misguided sense of impunity.

3) We failed to learn from the follies of history.

Having gone badly wrong when first cutting fat, we had an opportunity to focus instead on food choice and dietary pattern. Instead, counter-claims of debate invited a sequential focus on one nutrient at a time that prevails to this day. We cut fat, and invented a way to eat badly. We cut carbs, and did much the same. These days, a growing bounty of gluten-free junk foods is readily available. These repeated trials and disappointments have led only to a relative distrust of, if not disgust with, dietary guidance.

4) We gave everyone a megaphone.

With the advent of cyberspace and the blogosphere, we gave everyone a megaphone. That took a diversity of opinions, some expert and some clearly not, and turned them into an endless cacophony of echoes. We've created a situation in which it is very hard to discern any reliable signal above the volume of static we produce.

To the extent a debate is about both sides making competing noise, its consummation after all these years may depend on relative quiet. The 2015 Dietary Guidelines Advisory Committee wisely chose to deemphasize nutrients, and instead to emphasize foods. A diet of wholesome foods in sensible combinations, predominantly plants, reliably sorts out fat intake along with all other nutrients. Focus on any given nutrient, and the resulting foods and dietary pattern are as apt to turn out badly as well; more so, if history is reliably indicative.

Some of the best foods for health- vegetables, fruits, beans, lentils- are natively low in fat. Some- nuts, seeds, avocado, salmon- are quite high in fat. Some of the world's best diets are quite low in fat, others quite a bit higher. What they share is a focus on food, not too much, mostly plants.

The cap on dietary fat has, indeed, long outlived any utility it ever had. So, too, has a big, fat debate that has diverted us for far too long to nutrients, from the foods that would be a far more constructive, and healthy focus.

Fat-Savvy Check List:

  • Total fat content: The world's longest-lived, healthiest populations have diets that vary widely in total fat content, but in all cases emphasize minimally processed foods, mostly plants. The total fat content of a diet is not a reliable indicator of diet quality; health-promoting diets can be quite low, or rather high, in total fat content.
  • Unsaturated fat: A balanced intake of unsaturated fats from nuts, seeds, avocado, olives/olive oil, and fish has consistently been associated with health benefits.
  • Saturated fat: Saturated fat is a diverse class of compounds, some of which may be neutral in their health effects. This class of fat, however, has not been associated with specific health benefits.
  • Trans fats: With its recent action, the FDA has effectively "banned" trans fat from routine use in the U.S. food supply; these fats will be exiting over the next several years. In the interim, partially hydrogenated oil may still be found in some baked goods, chips, fried foods, refrigerator dough, creamers and margarine. Look for it on ingredient lists, and avoid it.
  • Recommended eating: The short list of foods most decisively and consistently associated with health benefit includes foods both low (vegetables, fruits, whole grains, beans, legumes) and high (nuts, seeds, olive oil, fish) in fat.
  • Sources: Katz DL, Meller S. Can we say what diet is best for health? Annu Rev Public Health. 2014;35:83-103; Buettner D. The Blue Zones Solution: Eating and Living Like the World's Healthiest People. National Geographic: 2015; Scientific Report of the 2015 Dietary Guidelines Advisory Committee:; Katz DL, Hu F. Knowing What to Eat, Refusing to Swallow It. The Huffington Post; 7/2/14


Director, Yale University Prevention Research Center; Griffin Hospital

Editor-in-Chief, Childhood Obesity

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