Dr. David Katz
MedicalResearch.com Interview with:
David L. Katz, MD, MPH, FACPM, FACP, FACLM
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.