Apples belong to the Rose family of plants and are joined in that family by a wide range of very popular foods, including apricots, plums, cherries, peaches, pears, raspberries, and almonds.
Foods in the Rose family are simply too diverse in their nutrient value to allow for any one single recommendation about the number of servings that we should consume from this family on a weekly basis. However, when focusing specifically on apples, several anti-cancer studies show daily intake of this fruit to provide better anti-cancer benefits than lesser amounts.
So there may be some truth to that old phrase, “An apple a day keeps the doctor away!”
Apples Amazing Polyphenols
In the past five years, no area of apple research has been more dynamic than the area of apple polyphenols. The balance of these phytonutrients in apples is far more unique than many researchers previously suspected. In terms of flavonols, quercetin is the primary phytonutrient found in apples, and it’s far more concentrated in the skin than in the pulp. Kaempferol and myricetin are also important apple flavonols. Chlorogenic acid is apple’s primary phenolic acid, and it’s found throughout the pulp and also in the skin. If apples are red, it’s because of their anthocyanins, which are largely restricted to the skin. When an apple is more uniformly red in color, or when its red color is deeper in hue, it’s because there are more anthocyanins. In terms of catechin polyphenols, epicatechin is the primary nutrient found in apples. The flavonoid phloridzin accounts for 98% of the flavonoids found in the apple seeds. The total polyphenol contents of apples range from about 1-7 grams/kilogram of fresh pulp, but this ratio gets much higher in the skin, underscoring the special value of apple skins for deriving optimal polyphenol benefits from this fruit. In fact, in animal studies, there is a very commonly used standardized apple extract called standardized apple peel polyphenol extract, or APPE.
You might wonder why apples end up with such an amazing array of polyphenols. In this context, it’s fascinating to see that recent research studies show polyphenols to be the favorite mechanism used by apples to protect themselves from UV-B radiation. Cells in the skin of apple that conduct photosynthesis are especially sensitive to UV-B light from the sun. Many of the polyphenols in the skin of apples can actually absorb UV-B light, and thereby prevent UV-B from damaging the photosynthetic cells in the apple skin. Polyphenols, then, are like the apple’s natural sunscreen.
It is also interesting to note that the amazing polyphenol content of apples is related to their easy browning when sliced open or bruised. Inside the cells of apple skin and pulp are enzymes called polyphenol oxidases, or PPOs. When the cells of the apple are sliced through or physically damaged when an apple is dropped, the PPOs start oxidizing the polyphenols in apples, and the result you see is a browning of the damaged apple portion. It’s important to handle apples delicately in order to protect their health-supportive polyphenols! (Also in this context, it’s worth mentioning that damaged apples not only turn brown from the oxidation of their polyphenols, but they also start releasing relatively large amounts of ethylene gas that can pose a risk to other undamaged apples. This phenomenon is why people say that “one bad apple can spoil the whole bunch.” Once again, the problem of ethylene gas from apple bruising or other damage underscores the importance of handling this amazing fruit with tender loving care and removing any damaged apples from groups of apples stored in bulk.)
Since most of the polyphenols in apples function as antioxidants, it’s not surprising to see so many health benefit studies focusing on the antioxidant benefits from apple. Particularly strong is the ability of apples to decrease oxidation of cell membrane fats. This benefit is especially important in our cardiovascular system since oxidation of fat (called lipid peroxidation) in the membranes of cells that line our blood vessels is a primary risk factor for clogging of the arteries (atherosclerosis) and other cardiovascular problems. Apples’ strong antioxidant benefits are also related to their ability to lower risk of asthma in numerous studies, and their ability to lower risk of lung cancer. In addition to their unusual polyphenol composition, apples also provides us with about 8 milligrams of vitamin C. While that amount is not a lot, it’s still important, especially since the recycling of vitamin C in our body depends on the presence of flavonoids and apples do an amazing job of providing us with those flavonoids.
The cardiovascular benefits of apples are well-documented in research studies, and they are closely associated with two aspects of apple nutrients: their water-soluble fiber (pectin) content, and their unusual mix of polyphenols. Total cholesterol and LDL-cholesterol are both decreased through regular intake of apples. In some studies, “regular intake” has meant apple intake very close to the level of one whole fresh apple per day. As mentioned earlier, the strong antioxidant composition of apples provides us with protection from possible oxidation of fats (called lipid peroxidation), including fats found in the bloodstream (like triglycerides) or fats found in the membranes of cells linking our blood vessels. Decreased lipid peroxidation is a key factor in lowering risk of many chronic heart problems. Recent research has shown that the quercetin content of apples also provides our cardiovascular system with anti-inflammatory benefits. (Our blood levels of C-reactive protein, or CRP, are reduced following consumption of apples and researchers believe that the quercetin content of apples is the primary reason for this drop in CRP.) What a fantastic combination of cardiovascular benefits from such a widely available and delicious fruit!
Benefits for Blood Sugar Regulation
This area of research on apple benefits is relatively new, but it’s already awakening the interest of an increasing number of food scientists. At many different levels, the polyphenols in apples are clearly capable of influencing our digestion and absorption of carbohydrates, and the overall impact of these changes is to improve regulation of our blood sugar. The impact of apple polyphenols on our carbohydrate processing includes:
- Slowing down of carbohydrate digestion. Quercetin and other flavonoids found in apples act to inhibit carbohydrate-digesting enzymes like alpha-amylase and alpha-glucosidase. When these enzymes are inhibited, carbohydrates are broken down less readily into simple sugars, and less load is placed on our bloodstream to accommodate more sugar.
- Reduction of glucose absorption. Polyphenols in apples clearly lower the rate of glucose absorption from our digestive tract. Once again, this change lessens the sugar load on our bloodstream.
- Stimulation of the pancreas to put out more insulin. Getting sugar out of our bloodstream often requires the help of insulin, a hormone produced by the beta cells of our pancreas. By telling the beta cells of our pancreas to produce more insulin, the polyphenols found in apple can help us clear more sugar from our blood and keep our blood sugar level in better balance.
- Stimulation of insulin receptors to latch on to more insulin and increase the flow of sugar out of our bloodstream and into our cells. In order for sugar to leave our bloodstream and enter our cells (especially our muscle cells), insulin receptors on those cells must bind together with the insulin hormone and create cell changes that will allow sugar to pass through the cell membrane and into the cell. (Muscle cells, for example, continuously need this uptake of sugar from the bloodstream in order to function.) Polyphenols in apples help to activate the muscle cell insulin receptors, and in this way, they help facilitate passage of sugar from our bloodstream up into our cells. Once again, the result is better blood sugar regulation in our bodies.
Apples Anti-Cancer Benefits
Although some preliminary results show apple benefits for several different cancer types (especially colon cancer and breast cancer), it’s the area of lung cancer benefits that stand out in the apple research. There are numerous studies involving vegetable/fruit intake and risk of lung cancer. The number of subjects in these studies numbers into the high hundreds of thousands. Although many research studies show an impressive ability of overall fruit and/or vegetable intake to lower lung cancer risk, very few individual fruits show up as protective against lung cancer. Except apples! It’s really quite remarkable how apples have been one of the few fruits to demonstrate this unique relationship with lung cancer risk reduction. (Interestingly, this same phenomenon has to some extent also been present in research on asthma.) Researchers aren’t certain why apples are so closely associated with reduction of lung cancer risk. Their antioxidant and anti-inflammatory benefits are definitely involved here, but they don’t fully explain why apples are such a standout in this health benefit area. We look forward to future research that will help shed light on this unique capacity in apples.
Apples Anti-Asthma Benefits
Like the lung cancer benefits of apples, the anti-asthma benefits have been somewhat surprising to health researchers. Multiple studies have shown apple intake to be associated with decreased risk of asthma. However, in some cases, the study findings have been even stronger. In one study, apples showed better risk reduction for asthma than total fruit-plus-vegetable intake combined! (That comparison might seem like a contradiction since fruit-plus-vegetable intake would clearly include apples. But in this particular study, it turned out that apples were not routinely consumed by fruit-plus-vegetable eaters, such that researchers could separate out a small group of study participants who regularly ate apples and could compare this group to other study participants who regularly ate fruits-plus-vegetables but did not include apples among their fruits.) Like the anti-cancer benefits of apples, apples’ anti-asthma benefits are definitely associated with the antioxidant and anti-inflammatory nutrients found in this fruit. However, there is very likely to be something else going on as well since apples appear to be a truly standout fruit in this regard.
Other Health Benefits
While not as developed as research in other areas, preliminary health benefits of apples have also been established for several age-related health problems, including macular degeneration of the eye and neurodegenerative problems, including Alzheimer’s disease. In animal studies, prevention of bone loss has also been an area of investigation, particularly related to the phloridizin content of apples.