Apples are a source of both soluble and insoluble fiber. Soluble fiber such as pectin actually helps to prevent cholesterol buildup in the lining of blood vessel walls, thus reducing the incident of atherosclerosis and heart disease. The insoluble fiber in apples provides bulk in the intestinal tract, holding water to cleanse and move food quickly through the digestive system. It is a good idea to eat apples with their skin. Almost half of the vitamin C content is just underneath the skin. Eating the skin also increases insoluble fiber content. Most of an apple's fragrance cells are also concentrated in the skin and as they ripen, the skin cells develop more aroma and flavor.