Walnuts are an energy-dense, high-calorie food. Most of their calories come from fat. Walnuts do not increase obesity risks when replacing other foods in a diet. They are also richer in polyunsaturated fats than most other nuts. Linoleic acid - an omega-6 fatty acid - is the most abundant fat. Trials have shown that replacing saturated fat with linoleic acid reduces total and LDL cholesterol. Evidence suggests linoleic acid improves insulin sensitivity and lowers blood pressure. Walnuts are the only nuts that contain significant amounts of alpha-linolenic acid (ALA).