Amazingly, Thanksgiving Day has already come and gone. As I write this, then, the somewhat euphemistic “holiday season” has begun. In a bizarre testament to the priorities of our culture, many are spending Black Friday - rather than in cozy, familial repose - in full-contact, retail roller derby. We have convinced ourselves that the right digestif for our signature annual indulgence is combat with other shoppers to purchase things friends and relatives likely don’t need and often don’t want, obligating them to reciprocate in kind if only out of remorse. The Got Junk guys are presumably looking on with anticipatory glee, knowing their payday reliably follows.
Our culture tells us this is how it ought to be, and we are nuts enough to go along with it. Nuts, then, are, today’s theme.
We begin with walnuts, which, on the off chance you didn’t get the memo, are really good for you. The literature on the health benefits of walnuts is extensive. My colleagues and I have contributed to that literature several times before, and just did so again with a paper in BMJ Open Diabetes Research & Care.
In our study, we followed up on prior evidence that walnuts appear to confer benefits in people with, and at risk for, type 2 diabetes. This time, we enrolled 112 overweight adults with prediabetes, the metabolic syndrome, or other clear evidence of high diabetes risk. Our principal aim was to see if walnuts could be added to the daily diet over an extended timeframe (6 months) to improve overall diet quality, without resulting in weight gain. Prior study has suggested that walnuts, despite their high calorie content, tend to have a favorable effect on appetite and weight, presumably because they are very satiating. Calories count, but counting them is certainly not the best way to combine satisfaction with weight control. Highly satiating foods, which help us get full and stay full, are best for that.
Secondarily, we were interested in the effects of walnut intake on various measures of cardiometabolic status and body composition. Finally, we wanted to find out if people given roughly 350 calories from walnuts daily automatically “made room” for those calories, or if they needed a bit of dietary counseling to do so.
Our results largely affirmed the hypotheses we were testing. Daily intake of walnuts significantly improved overall diet quality, measured objectively, and did so without causing weight gain. There is both an obvious and subtle component to this effect. The obvious contribution is direct; walnuts are highly nutritious, and adding them to the diet is apt to improve diet quality somewhat. The subtle contribution is indirect; if we add walnuts without gaining weight, it suggests that something is being displaced from our diet to make room. If that something is much less nutritious than the nuts, the benefit may be amplified: more of a good food, plus less of a “bad” (or at least less good) food. Our results suggest this effect.
With regard to dietary counseling, we found initial evidence of added benefit. When a dietitian provided study participants explicit guidance about making room for the walnut calories in their daily diets, waist circumference went down significantly, by about an inch on average. Without dietary counseling, both waist size and weight trended up slightly, although the changes seen were not significant.
As with our prior studies, we saw evidence of improvement in overall cardiometabolic health with walnut consumption. Here, our main measure was endothelial function, which essentially assesses the capacity of arteries to dilate and enhance blood flow. This improved significantly from baseline with walnuts, but did not differ from our control group, because they, too, showed some improvement, albeit less. This is a common effect in lifestyle intervention studies. People enrolled into such trials are, naturally, very focused on their health-related behaviors. If they wind up in the control group, they tend to make improvements in those behaviors even if asked not to do so. That tendency blunts our ability to isolate the intended treatment effects, and see between-group differences.
Our data painted a clear enough picture just the same. Walnuts are very good for people with and at risk for diabetes, and for that matter the rest of us. They can be added to the diet routinely without much if any risk of weight gain, because of their high satiety index. Some counseling from a dietitian about how best to make room for walnuts may enhance benefits, especially related to weight. We are, of course, left with many unanswered questions about optimal dose, frequency, and placement in the diet to name a few. Some questions can be answered with more analysis of the data we have; most await further study.
One other quick comment about walnuts before moving on. I have been privileged to attend several meetings of the Scientific Advisory Board of the California Walnut Commission, our research funder in this area. The group has funded high-quality studies of walnuts, overseen by this board, to the tune of some $15 million. To satisfy our societal preoccupation with active ingredients, many of the studies have attempted to isolate the beneficial factors in walnuts from among the obvious candidates: omega-3 fat; monounsaturated fat; vitamins; minerals; antioxidants; and fiber, to name a salient few. Whereas almost all results with walnuts have been impressive, the results with isolated components have been much less so. The active ingredient in walnuts is, apparently, walnuts.
Nuts remind us how we went wrong with regard to dietary fat. For one thing, we got carried away, and tossed out the baby with the bathwater. Nuts were the baby, rich in health-promoting unsaturated fats. At the height of our cultural fat phobia, nuts were off the menu, and this was clearly mistaken. For another, we made the even graver mistake, propagated for profit by Big Food, that any alternative to dietary fat was a good alternative. This was benighted nonsense from the start, with on-going reverberations today. Low-fat junk foods, for which Snackwells are a flag bearer, still abound. And we are told routinely that America runs on the offerings of a company most indelibly linked to doughnuts. As friend, colleague, and 2015 Dietary Guidelines Advisory Committee member, Dr. Frank Hu of Harvard said at the meeting of the American College of Lifestyle Medicine in Nashville: by and large, all nuts are good for us, with the obvious exception of doughnuts.
Which brings us to the wingnuts. Their voices have predominated in our dietary dialogues for far too long. They offer us fixations on nutrients that cost us the view of the forest through the trees. They offer us quick-fix fad diets that are to health what get-rich-quick schemes are to wealth. They offer us misinterpretations of science, and misguided advice - such as eating more meat, butter, and cheese, when the weight of evidence clearly says otherwise. They routinely ignore the confluent interests in diet of people, and the planet.
My request and plea this holiday season, which takes us from the debauchery of Thanksgiving to the penitence of the New Year’s resolution, is to renounce the wingnuts, and think about swallowing, at long last, what we know reliably about diet and health. I am not alone in pitching this proposition; I was privileged to co-chair a conference that elucidated the common ground of leading nutrition experts around the world, from vegan to Paleo. Where that conference ended, a campaign devoted to that consensus has just begun. In making a plea for dietary sense to prevail at last, my voice is just one in a large, global chorus.
We would likely all benefit by eating nuts, walnuts perhaps in particular, more often. We would benefit by eating doughnuts less so. We would benefit most by denying the wingnuts and hucksters an audience. May their dwindling influence figure among the gifts in the offing this holiday season.
David L. Katz, MD, MPH, FACPM, FACP, FACLM, is the Founding Director (1998) of Yale University’s Yale-Griffin Prevention Research Center, and current President of the American College of Lifestyle Medicine. He has published roughly 200 scientific articles and textbook chapters, and 15 books to date, including multiple editions of leading textbooks in both preventive medicine, and nutrition. He has made important contributions in the areas of lifestyle interventions for health promotion; nutrient profiling; behavior modification; holistic care; and evidence-based medicine. David earned his BA degree from Dartmouth College (1984); his MD from the Albert Einstein College of Medicine (1988); and his MPH from the Yale University School of Public Health (1993). He completed sequential residency training in Internal Medicine, and Preventive Medicine/Public Health. He is a two-time diplomate of the American Board of Internal Medicine, and a board-certified specialist in Preventive Medicine/Public Health. He has received two Honorary Doctorates.