In one study, subjects who consumed a diet that emphasized peanuts, in both nut and butter form, for one month demonstrated that their risk of heart disease dropped by 21% compared to those people who ate typical American/Western diet.
In another study, subjects who were given two or three servings of peanuts or peanut butter, had a reduction in both their LDL cholesterol and triglycerides levels. Those who ate peanut foods had results double the benefits of other subjects who had a low-fat diet.
(175.5 calories, 14.9g fat)
Peanut is not really a nut but a legume or bean, but it's been consumed as a nut and that's why it's in this list.
Peanuts are high in protein, monounsaturated fat and the antioxidant resveratrol, which makes them excellent at protecting the heart and blood vessels.