Apples are an excellent source of pectin, vitamin C, and fiber. They’re also a good source of potassium. The skin contains most of the apple’s important nutrients. Raw apples are higher in many nutrients and phytochemicals than cooked apples. Apples that are raw and unpeeled, are a great source of many important phytochemicals, such as ellagic acid and flavonoids (especially quercetin). For example, fresh whole apples and fresh apple juice contain approximately 100-130 milligrams per 100 grams (roughly 3 1/2 ounces) of chlorogenic, ellagic, and caffeic acids. In cooked or commercial apples, the content of these compounds is at or near zero.
Research has shown that the old saying “an apple a day keeps the doctor away” is true. In one of the studies, researchers in Finland followed more than 5,000 Finnish men and women for more than twenty years. Those who ate a lot of apples along with other flavonoid-rich foods, such as onions and tea, were found to have a 20 percent lower risk of heart disease than those who ate the smallest amount of those foods.
Apple consumption has also been linked to lower risk of asthma. Research found that people who ate at least two apples each week had a 22 to 32% lower risk of developing asthma than those who ate less of the fruit.
Researchers believe that the apple’s high content of flavonoids, like quercetin, are what contribute most to the fruit’s protective effects against heart disease and asthma. Pectin is a soluble fiber that has been shown to exert a number of beneficial effects. Apples are very high in pectin. Studies have found that pectin can lower cholesterol levels as well as improve the intestinal muscle’s ability to push waste through the gastrointestinal tract. Apples promote bowel regularity and relieve both constipation and diarrhea due to their insoluble fiber and pectin.