The latest nut to elbow its way into the health spotlight is the trusty walnut. New research suggests that anyone with risk factors for heart disease might want to snack on a handful a day.

In a recent study, Emilio Ros, chief of the Lipid Clinic at the Hospital Clinic of Barcelona, Spain, put 21 men and women with high cholesterol on a classic Mediterranean diet—vegetables, legumes, lean meats, fish, and up to 50 grams of olive oil per day for four weeks. They then replaced about a third of the calories the diners were getting from olive oil or other monosaturated fats with walnuts (about eight to 13 whole nuts).

After another four weeks, the volunteers’ cholesterol levels dropped further than they had on the Mediterranean diet. What’s more, their arteries dilated more easily. That’s potentially important for people with high blood pressure and diabetes, both conditions in which arteries don’t dilate properly.

Ros credits walnuts’ high levels of alpha-linolenic acid, a plant-based omega-3 fatty acid, with restoring the elasticity of arteries and improving blood flow. The nuts may also keep some cholesterol from being absorbed.