What makes apples healthy to eat?

USDA nutrient data base lists all compounds found in a medium size apple (100 grams or 4 ounces) at http://www.nal.usda.gov/fnic/foodcomp/cgi-bin/list_nut_edit.pl . But what within the array of compounds in an apple fruit makes it good for human health?  First,  apples are a great source of fiber.  If you ate a 100-g apple, 2.4 g would be fiber.  According to the Mayo clinic’s web site (http://www.mayoclinic.com/health/fiber/NU00033) apples provide soluble fiber which dissolves in water to form a gel-like material. Soluble fiber can lower blood cholesterol and glucose levels. Apples also contain vitamin C which can help boost immunity; vitamins A, E and beta carotene demonstrated to reduce cellular damage and lower the risk of asthma, diabetes and heart disease.  So an apple a day, can really help keep the doctor away.