Eating walnuts daily can ward off diabetes and heart disease in at-risk individuals, a new study has found.

Researchers from the Yale-Griffin Prevention Research Center in Connecticut found that daily intake of 56 g of walnuts improves endothelial function in overweight adults with visceral adiposity.

The study included a sample of 46 adults aged 30-75.

Participants had a Body Mass Index larger than 25, and a waist circumference exceeding 40 inches for men and 35 inches for women.

They were also required to be non-smokers, and all exhibited one or more additional risk factors for metabolic syndrome, a precursor of diabetes and cardiovascular disease.

The group was randomly assigned to two 8-week sequences of either a walnut-enriched ad libitum diet or an ad libitum diet without walnuts.

Those chosen for the walnut diet were instructed to consume 56 g of shelled, unroasted English walnuts per day as a snack or with a meal.

"We know that improving diets tends to be hard, but adding a single food is easy," explained Dr David Katz, Director of the Yale-Griffin Prevention Research Center and lead author of the research team.

"Our theory is that if a highly nutritious, satiating food like walnuts is added to the diet, there are dual benefits: the benefits of that nutrient rich addition and removal of the less nutritious foods," Katz said.

The research found that daily intake of 56 g of walnuts improves endothelial function in overweight adults with visceral adiposity.

"The primary outcome measure was the change in flow-mediated vasodilatation (FMD) of the brachial artery," researchers said.

"Secondary measures included serum lipid panel, fasting glucose and insulin, Homeostasis Model Assessment-Insulin Resistance values, blood pressure, and anthropometric measures.

"FMD improved significantly from baseline when subjects consumed a walnut-enriched diet as compared with the control diet. Beneficial trends in systolic blood pressure reduction were seen, and maintenance of the baseline anthropometric values was also observed. Other measures were unaltered," they said.

The study is published in the Journal of the American College of Nutrition.