It's a commonly accepted fact that apples are good for you. The saying "An apple a day keeps the doctor away" reflects how well-established the correlation is between apples and health. Many people may not know what is behind these health claims about apples, and how good for the body apples are. The health benefits of apples come not only from the nutrients they contain but also from compounds called phytochemicals.

Apples are extremely high in phytochemicals, compounds that plants make to protect themselves that also have a healthy effect on the human body when consumed. The high levels of quercetin, kaempferol and myricetin also confer antioxidant properties. These flavonols, along with anthocyanins, chlorogenic acid and epicatechin protect the body from cancers and immune diseases. The highest levels of phytochemicals are found in the apple skins, and the compound procyanidin B2 contributes about 60 percent of the antioxidant activity in the peel, according to Science News.

Polyphenols and quercetin, two types of phytochemicals in apples, help regulate blood sugar. Quercetin may also be neuroprotective, helping you avoid Alzheimer's disease. A component in apples called phloridizin may help slow or prevent bone loss. The vitamin C in apples provides additional antioxidant activity beyond the action of apple phytochemicals.

Eating a whole apple is healthier than processed apple products, such as apple juice or applesauce. This is because different beneficial components in apples work together to provide more benefits overall than the individual components can provide alone. The soluble fiber pectin works in concert with phytonutrients in the apple to lower blood fat levels even further than pectin could by itself.

An apple a day truly seems to be the best way to consume this beneficial fruit. People who eat an apple every day are better protected against cancer than those who eat apples less frequently, explains World's Healthiest Foods. Apples should be consumed at least three to five times a week in a diet that includes four to five servings of fruit each day.

With thousands of different varieties on the market, choosing the best type of apple for health can be a daunting task. The varieties Red Delicious, Northern Spy and Ida Red have the highest levels of phytochemicals and antioxidant activity, according to a May 2005 Science News report. Of the apples studied, the Empire variety had the least antioxidant activity.