New research suggests that eating walnuts could improve overall diet and lower some health risk factors.

Researchers found that eating a daily handful of walnuts is linked to better overall diet quality and an improvement in certain risk factors among people at high risk of diabetes. Walnuts are a rich source of essential fatty acids and other nutrients, such as folate and vitamin E. And they have been associated with various health benefits. But they are also high in calories, prompting concerns that they might increase weight gain if not part of a calorie controlled diet.

"Our data suggest that inclusion of walnuts in the diet, with or without dietary counseling to adjust caloric intake, improved diet quality and may also improve [endothelial function], and reduce total and LDL cholesterol in this sample of adults at risk for diabetes," conclude the researchers.

For the study, researchers collected and analyzed data from more than 100 people. The participants were randomly assigned to either follow a diet with dietary counseling designed to curb calorie intake, or one without. Within these two groupings, participants were randomly assigned to the daily inclusion of 56 g (2 oz) of walnuts in their diet or the complete avoidance of walnuts for a period of six months.

Diet quality was assessed using the Healthy Eating Index 2010 (HEI-2010). Improved diet is associated with a better cardiovascular risk profile and a lowered risk of long term conditions.

After taking account of influential factors, such as age, calorie and fatty acid intakes, and the amount of regular exercise taken, the analysis indicated that adding walnuts to the daily diet was associated with improved diet quality.

A walnut-rich diet was also associated with significantly improved endothelial cell function, irrespective of dietary counseling to curb calorie intake.

Endothelial cells line the walls of all blood vessels in the body, forming a selectively permeable barrier between the blood and other body tissues, enabling certain chemicals and blood gases to pass through.

Total and 'bad' (LDL) cholesterol also fell significantly among those who ate walnuts every day.

However, endothelial function and cholesterol levels also improved among those following the walnut exclusion diet, possibly due to the placebo effect, suggest the researchers.

Body fat significantly increased on the walnut-rich diet, when eaten in the absence of calorie restriction, but waist circumference fell significantly when combined with calorie restriction.

Further studies in more diverse groups of people are warranted, they suggest.

The findings are detailed in the online journal BMJ Open Diabetes Research & Care.