A daily handful of walnuts reduces bad cholesterol in the elderly and protects against heart disease, a new study found.
And just one-and-a-half ounces of the nuts, high in polyunsaturated fats, can boost friendly bacteria in the gut which reduce inflammation and cholesterol - both of which contribute to heart disease.
They also reduce hungry and increased feeling full.
Every 28 grammes (1oz) of walnuts contains 13 grammes of polyunsaturated fat and they are the only nut with high levels of plant-based omega-3 fatty acid with 2.5 grammes per ounce serving.
The first findings from the Walnuts and Healthy Ageing (WAHA) study found daily walnut consumption reduced blood cholesterol levels without adverse effects on body weight among older adults.
WAHA was a two-year clinical trial conducted by researchers from the Hospital Clinic of Barcelona and Loma Linda University aimed at determining the effect of walnuts on age-related health issues.
Barcelona's Dr Emilio Ros said: "Given walnuts are a high-energy food, a prevailing concern has been that their long term consumption might be associated with weight gain,.
"The preliminary results of the WAHA study demonstrate that daily consumption of walnuts for one year by a sizeable cohort of ageing free-living persons has no adverse effects on body weight.
"They also show that the well-known cholesterol-lowering effect of walnut diets works equally well in the elderly and is maintained in the long term.
"Acquiring the good fats and other nutrients from walnuts while keeping adiposity at bay and reducing blood cholesterol levels are important to overall nutritional well-being of ageing adults.
"It's encouraging to see that eating walnuts may benefit this particular population."
The study followed 707 healthy older adults who added daily doses of walnuts which was equivalent to a sixth of caloric intake to their typical diet or to consume their usual diet without nuts.
After a year, the study found that both diets had minimal effect on body weight, triglycerides, and HDL cholesterol.
However, the walnut-diet resulted in significant LDL cholesterol reductions compared to the control, nut-free diet.
Dr Ros added: "As we continue the WAHA study, we will assess how walnut consumption may affect, among other outcomes, cognitive decline and age-related macular degeneration, conditions that were major public health concerns."
Other studies presented at at Experimental Biology 2016 in San Diego suggested walnuts improved gut health, hunger and satiety, and metabolic health.
Researchers from the US's Agricultural Research Service found one-and-a-half ounces a day significantly affected gut bacteria favourable to decrease inflammation and cholesterol.
And a University of Georgia study found the types of fat eaten on a daily basis can alter long-term appetite responses, such as hunger and satiety.
After consuming high-fat meals rich in saturated fat, 18 sedentary adults of normal weight were randomly assigned to consume either a diet high in polyunsaturated fat or a control diet for the next seven days.
Those who ate a diet high in polyunsaturated fat favourably alters hunger and satiety markers.
Oregon State University looked at the addition of walnuts and polyphenol-rich foods to a typical high-fat Western diet and a walnut-diet supplemented with polyphenol-rich foods such as raspberries, cherries or green tea may help reduce inflammation.
All studies supported in part by the California Walnut Commission (CWC) were published in The Federation of American Societies for Experimental Biology Journal.