Dr. David Katz
Director, Yale University Prevention Research Center
President, American College of Lifestyle Medicine
Founder, True Health Initiative
Medical Research: What is the background for this study? What are the main findings?
Dr. Katz: the evidence that nuts in general, and walnuts in particular, have health promoting properties is vast and conclusive. In our own prior research, we have shown that daily ingestion of walnuts ameliorates overall cardiac risk in type 2 diabetics (http://www.ncbi.nlm.nih.gov/pubmed/19880586) and that the same intervention improves cardiac risk and body composition in adults at risk for diabetes (http://www.ncbi.nlm.nih.gov/pubmed/23756586). Our prior studies, and work by others, suggest that despite their energy density, walnuts may exert a favorable influence on calorie intake and weight, because of their very high satiety factor. We also know that walnuts are highly nutritious overall, and suspect that those who add walnuts to their diets are apt to ‘bump’ something less nutritious out, thereby improving the overall quality of their diets as measured objectively.
Accordingly, we designed the new study to look at the effects of daily walnut ingestion on diet quality, weight, and cardiac risk measures in a larger cohort of adults at risk for type 2 diabetes (ie, central obesity, indications of insulin resistance) over a longer period of time. We also wondered whether the addition of some 350 daily calories from walnuts would result in the displacement of a comparable number of calories from other sources, so we compared the effects of the intervention with, and without, counseling to help people ‘make room’ for the walnut calories.
We found again that walnuts improved overall cardiac risk status, as measured by endothelial function- essentially, a direct measure of blood vessel health and blood flow. We also found that adding walnuts to the diet significantly improved overall diet quality, and did not lead to weight gain. Walnuts also improved the lipid profile. When walnut intake was combined with counseling for overall calorie intake, there was a significant decline in waist circumference.
Medical Research: What should clinicians and patients take away from your report?
Dr. Katz: Walnuts are a highly nutritious, satiating food. Their addition to the diet is apt to improve diet quality overall, and key measures of cardiometabolic health. Those benefits are apt to be enhanced if patients get some counseling about ‘making room’ for the calories from the nuts. In particular, the benefits of adding walnuts to the diet are apt to be amplified if clinicians address the issue of dietary substitution, namely: “eat more of this, and make room for it by eating less of that…” this approach has the potential to enhance diet, and health, in two ways: by adding high quality foods, and by removing lower quality foods. Walnuts in place of common snack foods, for instance, would potentially produce health effects based both on what is added, and what is removed.
There appears to be particular benefit of walnut ingestion among adults with risk factors for diabetes, which is an enormous segment of the population.
We did see some increase in body fat when walnuts were consumed daily without calorie counseling, so we add the proviso that dosing is important, and that even an excellent food, if overeaten, or if added to a diet excessive in total calories, can contribute to weight gain.
However, walnuts seem to be highly satiating, and appear to have great potential to help control appetite, and total calorie intake- and more research is warranted to look specifically at how walnuts can be used to help facilitate energy balance over time.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Katz: As noted, we are very intrigued at the prospect of improving diet quality and health, and with the same strategy, facilitating weight control by enhancing satiety. So we are now looking at protocols that dose walnuts in various ways to enhance satiety, and potentially combine the beneficial metabolic effects we’ve seen thus far with even greater effects on weight loss/weight control, and improvements in body composition.
Nutrition – Obesity: Body Composition:
Valentine Njike, Rockiy Ayettey, Paul Petraro, Judith Treu, and David Katz
Walnut Ingestion in Adults at Risk for Diabetes: Effects on Diet Quality, Body Composition, and Cardiac Risk MeasuresFASEB J April 2015 29:747.15