Walnuts are low in saturated fat and high in both polyunsaturated and mono-unsaturated fat. Walnuts are an excellent source of omega-3 and omega-6 fatty acids, particularly when bought in their shells and eaten while fresh. Walnuts contain no cholesterol and are an important source of dietary fiber and protein. They are also a good source of many vitamins and minerals including potassium, magnesium, phosphorus, copper, zinc, vitamin B1, B6, folate, and vitamin E. Eating a handful of walnuts a day can lower blood cholesterol.