Expert Opinion on Dietary Fat: Is the Apparent Disagreement Real?

Expert Opinion on Dietary Fat: Is the Apparent Disagreement Real?
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Answers are seldom, if ever, better than the questions that invite them. We will return to that in due course. (And yes, that luscious Lamborghini figures in it -- sort of.)

I had the enormous privilege over the past two days of co-chairing a genuinely groundbreaking nutrition conference in Boston. Sponsored by Oldways, the conference convened very diverse experts from around the world, and tasked us all with mapping out the "common ground" of healthy eating. We did so, in gratifyingly decisive style.

But the relevant electrons had only just submitted to the discipline of word processing, and I had not yet left the conference venue when I received an email from one of the attending journalists, hoisting the proverbial red flag. She alerted me that she had received a question from one of her many readers about the best dietary approach for addressing dyslipidemia, and avoiding statins. Specifically, the reader inquired: Should I, or shouldn't I, adopt a low-fat diet?

The journalist, in turn, took advantage of her circumstance to pose that question directly to two of the scientists at the meeting, members of the group that had allegedly just come to agreement. One of the two is widely known for studies of, and devotion to, low-fat, plant-based diets. The other is a prominent nutritional epidemiologist without any obvious allegiance to a specific dietary pattern, but seemingly most inclined toward the Mediterranean diet.

So, when the reader's question -- should I use a low-fat diet to address my dyslipidemia? -- was posed by the journalist to these two august members of our assembly, one said "yes," and the other said "no."

There are few responses with less ostensible overlap than "yes" and "no," and the journalist shared her concern with me accordingly. Given this response, in the immediate aftermath of our purported consensus, was the claim of consensus valid?

Yes, it was. The deficiency here is less a matter of diverging answers, and more a matter of a divisive, and ultimately misdirected, question. In other words, the trouble here is not want of consensus. The trouble here, to borrow from Cool Hand Luke, is a failure to communicate well.

The reader's question here, a question we have taught the public to pose by fixating on nutrients rather than foods for decades, invites mutually exclusive replies from experts with differing preferences. That does not belie the true consensus; it merely obscures it. Consider, for instance, asking top engineers from, say, Lamborghini and Bentley: Are the world's best performance cars made in Italy (or if you prefer, England)? The Lamorghini engineer, deeply invested in that culture, would doubtless say yes (for Italy). The Bentley engineer would just as reliably say no, defending the handcrafted virtues of her own brand. Again we have the unbridgeable divide between "yes" and "no" from two experts.

But the problem here obviously resides with the question. If both engineers were instead asked -- what are some of the world's most finely engineered performance automobiles? -- we might quite reasonably expect that each would mention the other's brand, along with their own, and several others, however begrudgingly.

So, too, I believe, for dietary fat. Some researchers have devoted entire careers to studies of outstanding, plant-based diets that are, along with many other attributes, low in total fat. Health outcomes have been excellent in such trials, and those invested in this line of inquiry would, naturally, recommend a low-fat diet for modifying cardiac risk. What they actually mean, however, is an outstanding diet, composed of wholesome, highly nutritious foods -- that happens to be low in total fat.

Other researchers have devoted entire careers to studies of the Mediterranean diet, the best variants of which are also outstanding, and composed of wholesome, highly nutritious foods. Such diets also happen to be relatively high in total fat. Experts with careers devoted to inquiry in this area would naturally recommend a Mediterranean diet for cardiac risk mitigation.

Note that both agree on the subordinate details, as does the larger universe of nutrition experts. All variants on the theme of optimal eating reliably exclude manufactured trans fats, and are low in total saturated fat -- if only by virtue of the foods they emphasize. They are, into the bargain, low in added sugars and sweeteners; low in refined grains and starches; and not more than moderate in total sodium. These matters are not belabored here for they are uncontentious, and largely self-evident.

Imagine asking the expert devoted to plant-based, low-fat diets: MUST a diet be low in total fat to be excellent? I am confident that most who truly warrant the "expert" designation would say no, while perhaps appending that they believe the diet may be made even more excellent by keeping total fat low. Conversely, were the Mediterranean diet expert asked -- MUST a diet be high in total fat to be excellent? -- I am again fairly confident they would concede it need not be, while perhaps appending that a generous intake of the right dietary fats might well make a diet even more excellent.

These two responses still represent the differing priorities of distinct experts, but they allow quite handily not only for common ground, but more ground in common than uncommon to both. That was the very intent of the conference, to demonstrate the predominance of common ground, not to disallow for additional real estate where we might find room to disperse, and ruminate in private.

Better still than this approach to the reader's question is an approach that looks past the issue of macronutrient thresholds in the first place. Outstanding diets can be higher or lower in total fat, higher or lower in total carbohydrate, and higher or lower in total protein. They cannot fail, however, to emphasize wholesome foods in sensible combinations, a preferential focus on plants. They cannot fail to avoid hyper-processed, glow-in-the-dark junk.

So, imagine an answer to the reader's question that goes like this:

Some experts would direct you to a low-fat diet, and some to relatively high-fat diet, but most would suggest you not think about total dietary fat at all, but rather what kind of fat, and from which foods. What experts agree on is that diets that happen to be low fat, because they are made up of wholesome, healthful foods that are low in fat; and diets that are much higher in fat, because they are made up of wholesome, healthful foods that are higher in fat -- have both been associated with astonishing improvements in overall health, including the reversal of cardiac risk factors, and the prevention of heart attacks. Both such dietary patterns have been associated with the effects on blood lipids you are seeking. A particular diet tested for effects on serum lipids to rival those of statin drugs did not focus on fat at all, but rather on soluble fiber and plant sterols.

So: Start out by eating a dietary pattern that emphasizes unprocessed and minimally processed vegetables, fruits, whole grains, beans, lentils, nuts, and seeds. This will tend to be rather low in fat. You might, then, choose to place particular emphasis on the nuts; add avocado, olives, olive oil, fish, and seafood -- and perhaps some dairy -- and your fat intake might well wind up rather high. But you are still safely in the realm of evidence-based disease prevention/health promotion by dietary means. Drink water when thirsty, by the way; and perhaps modest alcohol, preferentially red wine, to enhance the pleasure of meals and cardiovascular health as well. Everything else is rather discretionary. You might or might not choose to include some lean meat; some poultry; some eggs. These foods can be included at certain levels in very healthful diets, but these foods do not seem to be what make any given diet healthful -- so the emphasis should clearly be elsewhere.

Experts are people, and people will inevitably tend to favor the variant on some theme to which they have devoted their careers and lives. That's the very reason the "common ground" matters. There are, in fact, low and high fat regions of it, but there are NO "bad fat" regions of it. When fat is high, it comes from foods that even low fat proponents mostly endorse; when fat is low, it is because of foods that high fat proponents endorse.

I have heard colleagues, notably from Harvard, say "there is no evidence for low-fat diets." This statement, however, is so readily falsifiable as to be a non sequitur. In fact, even Medicare, generally about as open-minded and persuadable as a Spanish Inquisitor, acknowledges such evidence, and reimburses on the basis of it.

What I believe these colleagues actually mean is that: There is no evidence that a diet must be low in total fat to produce health-promoting, disease-preventing effects. There is no evidence that when excellent, low-fat diets achieve outstanding health effects, it is specifically because they are low in total fat. Both of those statements are, to the best of my knowledge, eminently defensible if not just plain true. The difference between the assertion and what it really means is, as noted, less about content expertise, and more about the subtleties of communication, where much of our failure resides.

Similarly, I have heard colleagues argue the virtues of low-fat diets, but they are, ineluctably, talking about excellent diets that happen to be low in fat because of the native characteristics of the foods that predominate. Broccoli is not good for us because it is low in fat; broccoli is good for us because it is broccoli.

Which brings us full circle: There are no good answers to dubious questions. Questions about total fat intake, or fixations on any single nutrient for that matter, tend to be rather dubious, and invite answers that are divisive. They do not belie the common ground -- but they do ask us to retreat to our exclusive patches of real estate, and sing out their competing virtues.

There truly is common ground among the world's leading nutrition experts. The journalist's reader may favorably adjust her lipid profile with an excellent diet that happens to be higher, or lower, in total fat. The seemingly irreconcilable experts would be able to give complementary rather than conflicting answers were we to overcome the challenges of communication, and learn to start asking better questions.


Director, Yale University Prevention Research Center; Griffin Hospital

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