Monday, July 27, 2015
Nutrients, nutritionism, and historical nuttiness
The current issue of JAMA features a commentary by two colleagues, calling for an end to what they term the “ban” on total dietary fat. More specifically, the authors are endorsing the report of the 2015 Dietary Guidelines Advisory Committee, of which I too am a fan, in which there is no specific reference to an upper limit for total dietary fat intake.
There are a number of important implications in this.
First, the case for abandoning an emphasis on limiting total dietary fat intake is clearly legitimate and overdue. The world's healthiest populations vary widely in their total dietary fat intake, but vary far less in the basic theme of their diets. In all cases, they consume diets of wholesome foods in sensible combinations; real foods, not too much mostly plants- to borrow from Michael Pollan.
We have long had abundant evidence that reference to total dietary fat was a stark failure to differentiate baby and bathwater. Some classes of fat, notably manufactured trans fats, are consistently and uncontestably harmful. Some classes of fat contain specific members that are harmful and others that may be innocuous; this is where the evidence currently stands for saturated fat. The current enthusiasm for attributing health benefits to saturated fats may be a product of wishful thinking, reactionary excess, or ulterior motives, but is not a product of the current weight of scientific evidence. Of note, the Dietary Guidelines Advisory Committee report, and the new commentary in JAMA, both preserve the recommendation to limit total saturated fat intake.
Some fats may be beneficial or harmful, depending on total dose and proportion to their counterparts; this is our current understanding of omega-6 polyunsaturates. Like omega-3 fats, omega-6 fats are essential nutrients; but we are prone in modern diets to a relative deficiency of the former, and a relative excess of the latter. Because our intake of omega-3 polyunsaturates tends to be relatively low and these fats are essential nutrients, more would be better in most cases. Monounsaturated fats, indelibly associated with the Mediterranean diet, are generally thought to be health promoting.
Second, as noted in the JAMA piece, we have other nutrients of concern these days. Our fixation on fat for many years resulted in marked increases in our intake of refined grains and added sugars. These are both major liabilities of the modern diet, and an obsolete emphasis on limiting total fat intake may lead inadvertently to ills in this other direction.
Third, there has long been a disconnect between the lingering reference to total fat and recommendations for specific foods. Fish, especially fatty fish, are consistently associated with health benefits, and are recommended in the Dietary Guidelines for Americans. The health benefits of the very-high-fat avocado are widely recognized. And, in particular, nuts and seeds are consistently and decisively associated with health benefits, and recommended rather prominently in both the 2010 Dietary Guidelines for Americans, and the 2015 advisory committee report. It does not make a lot of sense to advise limiting intake of nutrients while advising increased consumption of foods in which those nutrients are found.
Fourth, and finally, there is the precautionary tale of our recent nutritional history, which has been, in a word, nutty. For literal decades now, we have fixated on some particular nutrient while looking right past foods, and overlooking the overall dietary pattern. We have managed to invent an unending variety of junk foods, each under the halo of some particular nutrient “virtue:” low fat; low carb; low fructose; vitamin fortified; gluten free. We have invented a parade of ways to eat badly, and are, predictably, mostly fatter and sicker as a result.
So while the plea in JAMA to lift the “ban” on total dietary fat is valid, the silence on the topic in the DGAC report may be even more so. The DGAC decided to de-emphasize nutrients altogether, and instead to emphasize the very items we have been overlooking, foods and dietary patterns. Their 572-page report is perhaps best encapsulated by this passage from the executive summary: “The overall body of evidence examined by the 2015 DGAC identifies that a healthy dietary pattern is higher in vegetables, fruits, whole grains, low- or non-fat dairy, seafood, legumes, and nuts; moderate in alcohol (among adults); lower in red and processed meats; and low in sugar-sweetened foods and drinks and refined grains. Additional strong evidence shows that it is not necessary to eliminate food groups or conform to a single dietary pattern to achieve healthy dietary patterns. Rather, individuals can combine foods in a variety of flexible ways to achieve healthy dietary patterns, and these strategies should be tailored to meet the individual's health needs, dietary preferences and cultural traditions. Current research also strongly demonstrates that regular physical activity promotes health and reduces chronic disease risk.”
While a cap on total dietary fat intake has proven to be unhelpful, it's worth noting that the wide range of variations on the theme of eating for optimal health all fall within a predictably judicious range. While some of the world's “best diet” contenders are very low in fat, and some as high as 40% of calories or more, none is extremely high. In all cases, though, this balance is achieved by an emphasis on foods. Diets proven in both research and real-world settings to be good for life-long health all emphasize vegetables, fruits, beans, lentils, and whole grains, all of which are natively low in fat. When these are prominent, or predominant, in a diet, there is a limit to how high in total fat that diet can be.
History is the best judge of our actions and inclinations. The judgment of our proclivity for mono-nutrient fixations has been rendered, and it is quite harsh; we have been harming ourselves with its unintended consequences for decades. In contrast, the 8 years of history since Michael Pollan wrote about “nutritionism” in the New York Times have judged his insight to be of profound importance. Get the foods right, and nutrients will take care of themselves; focus on any given nutrient, and there is good chance of inventing yet another way of eating badly.
When we know that some dietary fats are rather sinister, and others quite salutary, failure to unbundle the two is obsolete nonsense. When we know we are prone to remove healthful fats from our diets and replace them with sugar, an emphasis on total fat intake in dietary guidance is obsolete nonsense. A clear verdict has been rendered in the case of nutritionism, and it is guilty of crimes against humanity.
But let's be careful. The right response is not to canonize the nutrients we once vilified, but to de-emphasize nutrients and emphasize wholesome foods. Recommending for the intake of nuts, but against the fat content of nuts, was always just plain nutty. Failure to learn from the follies of our nutritional history would be even more so.
David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.
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