Apples are rich in fiber, vitamins, flavonoids and antioxidants, and it appears the beneficial synergy between the many healthful compounds in apples is truly a key to staying healthy.
Apples contain both insoluble and soluble fiber. One medium (5 ounces) unpeeled apple provides over 3 grams of fiber, more than 10% of the daily fiber intake recommended by experts. Even without its peel, a medium apple provides 2.7 grams of fiber.
Apple's two types of fiber pack a double punch that can knock down cholesterol levels, reducing your risk of hardening of the arteries, heart attack, and stroke. Adding just one large apple (about 2/3 of a pound) to the daily diet has been shown to decrease serum cholesterol 8-11%. Eating 2 large apples a day has lowered cholesterol levels by up to 16%.
LDL cholesterol isn't the only harmful compound on apple's removal list. Pectin grabs toxins like the heavy metals lead and mercury, and ushers them out of the body. Both the soluble and insoluble fibers in apples have cancer-protective activity since they relieve constipation and send potentially toxic substances out with the stools.
When it comes to bowel regularity, apple's two types of fiber tackle the job—no matter what it is. Both the insoluble fiber in apples and their soluble fiber pectin help relieve constipation (thus helping to prevent diverticulosis and colon cancer). The insoluble fiber works like roughage, while the pectin, which is found primarily in the skin, acts as a stool softener by drawing water into the stool and increasing stool bulk. On the other hand, because pectin firms up an excessively loose stool, it's also used to treat diarrhea. One well-known over-the-counter diarrhea remedy, Kaopectate ™, actually contains an oxidized form of pectin.
A type of pigment in apples that helps provide their color, flavonoids have been extensively researched and found to help prevent heart disease. Apple skin and onions are the two major food sources of a potent flavonoid called quercitin. If, in addition to eating an apple a day, you add 2 tablespoons of onion and 4 cups of green tea (also rich in flavonoids) to your menu, you, like the men who consumed these foods in a study, may have a 32% lower risk of heart attack than people who consume less of these foods.
Apples are also an excellent source of antioxidants, and when compared to many other commonly consumed fruits in the United States, were found to have the second highest level of antioxidant activity. Many of the phytochemicals found in apples, including quercetin, catechin, phloridzin and chlorogenic acid, are strong antioxidants.
Whole apples, especially their peels, have been found to have a number of powerful antioxidant effects, one of which is to protect VLDL and LDL (bad) cholesterol from oxidation. Yet when quercitin, one of the most important antioxidant flavonoids in apples, was tested by itself in rats, it had no protective effect. And when apple flesh and apple juice were tested, they provided less than a tenth the benefit of whole apple.
Quercitin's benefits derive from its antioxidant activity, especially when it teams up with another antioxidant, vitamin C, also found in apples, to bolster the body's immune defenses. This dynamic antioxidant duo provides another way (in addition to fiber) through which apples protect against cancer and also helps prevent the free radical damage to LDL cholesterol that promotes heart disease.
Whole apple extracts—in amounts comparable to human consumption of one, three or six apples a day—were shown to prevent breast cancer in test animals in a study published in the March 2005 issue of the Journal of Agricultural and Food Chemistry. And apples worked in a dose-dependent manner; the more apples eaten, the more protection. They concluded that as yet unknown constituents contribute to apples' potent protective qualities.
In the United States, 22% of the phenolic compounds consumed from fruits come from apples, making them the largest source of phenols in the American diet. When compared to other fruits, apples ranked second in total concentration of phenolic compounds, and perhaps more importantly, had the highest portion of free phenols. Since free phenols are not bound to other compounds in the fruit, they may be more available for absorption into the bloodstream.
Apples' protective effects against free radical damage to cholesterol reach their peak at three hours following apple consumption and drop off after 24 hours, providing yet another good reason to eat a whole fresh apple a day.
In the most recent studies, investigators found that the combination of apple pectin and apple phenols lowered cholesterol and triglycerides to a much greater extent than either apple pectin or phenols alone. This again suggests a beneficial synergy between the many healthful compounds found in apples and supports eating the whole fruit instead of simply drinking apple juice, eating peel-free applesauce or taking fiber supplements.
A new study suggests that eating and drinking apples and apple juice, in conjunction with a balanced diet, can protect the brain from the effects of oxidative stress. Although more research is needed, these brain health findings are encouraging for all individuals who are interested in staying mentally sharp as they age.
In addition to their beneficial effects against chronic diseases including cancer, cardiovascular disease, asthma and diabetes, apples may also help combat cholera. Recently, crude extracts from immature apples were found to inhibit cholera toxin in a dose dependent manner by up to 98%.
And if you want to reduce your risk of calcium oxalate kidney stones, drink apple juice. A study published in the August 2003 issue of the British Journal of Nutrition found that when women drank ½ to 1 liter of apple, grapefruit or orange juice daily, their urinary pH value and citric acid excretion increased, significantly dropping their risk of forming calcium oxalate stones.
It also now appears that the phenols in the skin of certain cultivars of apples may also provide a hefty dose of UV-B protection.
Apple phytochemical content is not greatly affected by storage. After 100 days, the amount of phenolic compounds in the skin begins to decrease slightly, but even after 200 hundred days in cold storage, the total amount of these compounds remains close to the level at the time of harvest.
However, processing apples into juice greatly lowers their phytochemical content. Apple juice obtained from Jonagold apples by pulping and straight pressing had only 10% of the antioxidant activity of fresh apples, while juice obtained after pulp enzyming had only 3% of fresh apples' antioxidant activity. The take home message: store apples in the refrigerator and enjoy a sweet, crunchy, whole apple at least 2-3 times each week.