Daily consumption of walnuts, rich in polyunsaturated fatty acids, may improve the health of blood vessels, thereby decreasing the risk of heart disease, says a new study from Yale. Supplementing the diet of middle aged diabetics with 56 grams of walnuts led to significant improvements in the function of the blood vessel lining (endothelium), and there was also a trend towards improved cholesterol levels, according to findings published in Diabetes Care.

The study adds to a growing body of science supporting the health benefits, and the heart benefits in particular, of increased consumption of nuts. Previous studies have reported benefits for almonds, macadamia, and pistachios.

Indeed, a recent study funded by the California Walnut Commission found that the fatty acids present in walnuts and fish oil may work in different ways to reduce the risk of coronary heart disease. According to findings published in the American Journal of Clinical Nutrition (May 2009, Vol. 89, pp. 1657S-1663S), a diet supplemented with walnuts led to reductions in cholesterol levels, while a fish diet led to reductions in blood levels of triglycerides.

For the new study, David Katz and his co-workers from the Yale University School of Medicine recruited 24 type-2 diabetics with an average age of 5, and randomly assigned them to a diet with or without 56 grams of walnuts for eight weeks.

At the end of the intervention period, blood flow was measured using flow-mediated dilatation (FMD) and found to have “significantly improved” by 2.2 per cent in the walnut group, compared to 1.2 per cent in the non-supplemented group.

Furthermore, blood sugar levels, and total cholesterol levels were also decreased from baseline values. However, these values did not reach significance compared to the non-walnut eating group. “A walnut-enriched diet improves endothelium-dependent vasodilatation in type 2 diabetics, suggesting a potential reduction in overall cardiac risk,” concluded the researchers. Further studies are needed to further elucidate the effects of walnuts in type-2 diabetics and larger studies are required to support the findings of this small study.

Diabetic stats

An estimated 19 million people are affected by diabetes in Europe, equal to 4% of the total population. This figure is projected to increase to 26 million by 2030. In the US, there are almost 24 million people with diabetes, equal to 8% of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.

Effects of Walnut Consumption on Endothelial Function in Type 2 Diabetics: A Randomized, Controlled, Cross-Over Trial.

Objective: To determine the effects of daily walnut consumption on endothelial function, cardiovascular biomarkers, and anthropometric measures in type 2 diabetics. Methods: This study was a randomized, controlled, single-blind, cross-over trial. Twenty-four participants with type 2 diabetes (mean age 58 years; 14 women, 10 men) were randomly assigned to one of the two possible sequence permutations to receive an diet enriched with 56 g (366 kcal) of walnuts per day and an diet without walnuts for 8 weeks. Subjects underwent endothelial function testing (measured as flow-mediated dilatation or FMD) and assessment of cardiovascular biomarkers before and after each 8-week treatment phase. The primary outcome measure was the change in FMD after 8 weeks. Secondary outcome measures included changes in plasma lipids, HbA1c, fasting glucose, insulin sensitivity, and anthropometric measures. Results: Endothelial function significantly improved after consumption of a walnut-enriched diet compared to an diet without walnuts (2.2 +/- 1.7 % vs. 1.2 +/- 1.6 %; p=0.04). The walnut-enriched diet increased fasting serum glucose, lowered serum total cholesterol and low-density lipoprotein cholesterol from baseline (10.0 +/- 20.5 mg/dL; p=0.04, -9.7 +/- 14.5 mg/dL; p<0.01; and -7.7 +/- 10 mg/dL; p<0.01 respectively), though these changes were not significant when compared to an diet without walnuts. There were no significant changes in anthropometric measures, plasma HbA1c, and insulin sensitivity. Conclusions: A walnut-enriched diet improves endothelium-dependent vasodilatation in type 2 diabetics, suggesting a potential reduction in overall cardiac risk.

Diabetes Care. 2009 Oct 30

PMID: 19880586