The phytonutrients in apples can help you regulate your blood sugar. Recent research has shown that apple polyphenols can help prevent spikes in blood sugar through a variety of mechanisms. Flavonoids like quercetin found in apples can inhibit enzymes like alpha-amylase and alpha-glucosidase.
Since these enzymes are involved in the breakdown of complex carbohydrates into simple sugars, your blood sugar has fewer simple sugars to deal with when these enzymes are inhibited. In addition, the polyphenols in apple have been shown to lessen absorption of glucose from the digestive tract; to stimulate the beta cells of the pancreas to secrete insulin; and to increase uptake of glucose from the blood via stimulation of insulin receptors.
All of these mechanisms triggered by apple polyphenols can make it easier for you to regulate your blood sugar.
Even though apple is not an excellent source of dietary fiber (it ranks as a “good” source in our WHFoods Rating System), the fiber found in apple may combine with other apple nutrients to provide you with the kind of health benefits you would ordinarily only associate with much higher amounts of dietary fiber. These health benefits are particularly important in prevention of heart disease through healthy regulation of blood fat levels. Recent research has shown that intake of apples in their whole food form can significantly lower many of our blood fats. The fat-lowering effects of apple have traditionally been associated with its soluble fiber content, and in particular, with the soluble fiber portion of its polysaccharide component known as pectins. What we now know, however, is that whole apples only contain approximately 2-3 grams of fiber per 3.5 ounces, and that pectins account for less than 50% of this total fiber.
Nevertheless, this relatively modest amount of pectins found in whole apples has now been shown to interact with other apple phytonutrients to give us the kind of blood fat lowering effects that would typically be associated with much higher amounts of soluble fiber intake. In recent comparisons with laboratory animals, the blood fat lowering effects of whole apple were shown to be greatly reduced when whole apples were eliminated from the diet and replaced by pectins alone. In summary, it’s not fiber alone that explains the cardiovascular benefits of apple, but the interaction of fiber with other phytonutrients in this wonderful fruit. If you want the full cardiovascular benefits of apples, it’s the whole food form that you’ll want to choose. Only this form can provide you with those unique fiber-plus-phytonutrient combinations.
The whole food form of apples is also important if you want full satisfaction from eating them. Researchers have recently compared intake of whole apples to intake of applesauce and apple juice, only to discover that people report less hunger (and better satiety, or food satisfaction) after eating whole apples than after eating applesauce or drinking apple juice. But especially interesting was an additional finding about calorie intake following apple consumption.
When healthy adults consumed one medium-sized apple approximately 15 minutes before a meal, their caloric intake at that meal decreased by an average of 15%. Since meals in this study averaged 1,240 calories, a reduction of 15% meant a reduction of 186 calories, or about 60 more calories than contained in a medium apple. For these researchers, “getting ahead” in calories with a net reduction of 60 calories was a welcomed outcome of the study, and an extra benefit to their study’s primary conclusion—the importance of whole apples (versus other more processed apple forms) in helping us manage our hunger and feeling more satisfied with our food.
Scientists have recently shown that important health benefits of apples may stem from their impact on bacteria in the digestive tract. In studies on laboratory animals, intake of apples is now known to significantly alter amounts of two bacteria (Clostridiales and Bacteriodes) in the large intestine.
As a result of these bacterial changes, metabolism in the large intestine is also changed, and many of these changes appear to provide health benefits. For example, due to bacterial changes in the large intestine, there appears to be more fuel available to the large intestine cells (in the form of butyric acid) after apple is consumed. We expect to see future studies confirming these results in humans, and we all to think about potential health benefits of apple that will be related to its impact on bacterial balance in our digestive tract.
Apple’s 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.
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 body.
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.
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.
Apples are a crisp, white-fleshed fruit with a red, yellow or green skin. The apple is actually a member of the Rose family, which may seem strange until we remember that roses make rose hips, which are fruits similar to the apple.
Apples have a moderately sweet, refreshing flavor and a tartness that is present to greater or lesser degree depending on the variety. For example, Golden and Red Delicious apples are mild and sweet, while Pippins and Granny Smith apples are notably brisk and tart. Tart apples, which best retain their texture during cooking, are often preferred for cooked desserts like apple pie, while Delicious apples and other sweeter varieties like Braeburn and Fuji apples are usually eaten raw.
Courtesy: WH Foods