Most vegetables and fruits provide little or no fat, and those containing fat, such as avocados and olives, contain mostly heart-healthy monounsaturated fats. Whole grains are also low in fat. Good low-fat sources of protein include beans and peas, skim milk, fish, tofu and lean meats.
A healthy diet gets between 20 and 35 percent of its calories from fat. Although too much fat in the diet contributes to weight gain and cardiovascular disease, too little prevents the body from absorbing and transporting the fat-soluble vitamins A, D, E and K. Fat also helps build up the body's energy reserves in the form of adipose tissue, which insulates vital organs and releases energy during physical activity.
Nutritionists divide dietary fats into polyunsaturated fats, monounsaturated fats, saturated fats and trans fatty acids. Food manufacturers create trans fatty acids by hydrogenating polyunsaturated fats. Trans fatty acids are solid at room temperature and have a longer shelf life than polyunsaturated fats. However, they also increase the risk of heart disease by interfering with the body's use of omega-3 fatty acids, raising levels of low-density lipoproteins and lowering levels of high-density lipoproteins.
Monosaturated fats and polyunsaturated fats have some heart benefits when used in moderation. Saturated fats are involved in cell regulatory functions and immune system functioning.