Experts agree that a diet based on moderation and variety is essential to good health. In other words, eating some of a wide variety of foods provides more complete nutrition and is more beneficial overall than a diet that relies on just a few foods. It is generally recommended to choose a diet that is low in saturated fat and cholesterol and moderate in total fat. Fatty meats and full-fat dairy products are the major sources of saturated fat in the diet. Sources of unsaturated fats are primarily vegetable oils. Diets higher in monounsaturated and polyunsaturated fats lower "bad" cholesterol levels, while saturated fats increase "bad" cholesterol. Therefore, an ideal diet would be higher in monounsaturated and polyunsaturated fats than the current North American diet.

source: http://www.eufic.org/pt/food/pag/food38/food381.htm