Take a look at the compelling new research on the antioxidant properties of common and exotic fruits.
Fruit just might be the ultimate food. Delicious and brimming with an array of vitamins and minerals, plus low in calories, fruit goes far beyond a glass of orange juice with breakfast. Recent studies suggest that berries, cherries, grapes, pomegranates and a plethora of exotic tropical goodies may help prevent cancer, heart disease and the age-related brain fuzzies.
But why visit the pharmacy for all this nutrition? Just pull up a chair at the breakfast table. Fifty years of scientific research have shown that the healthiest diets are loaded with fruits and vegetables. For decades, the main reason to eat fruit was thought to be vitamin C. Recently, though, a host of new tongue-twisting nutrient chemicals have dominated the discussion. Now the news is coming at us like an avalanche: More than 65 scientific studies have been published since 2004 on the antioxidants from bilberry (Vaccinium myrtillus) alone.
Fruits are especially rich in health-giving antioxidants, which help prevent cellular damage caused by free radicals. The powerful antioxidant compounds in fruits include an assortment of polyphenols (principally flavonoids), which are amazingly abundant in nature—there are more than 4,000 varieties.
Much of the antioxidant clout in fruit comes from the red, purple and blue pigments that give fruit its color. These pigments go by a lot of names—anthocyanins, anthocyanidins, proanthocyanidins and oligomeric proanthocyanidins. Generally, the darker the fruit, the more potent its antioxidant profile. Black currants, red currants, chokecherries and elderberries are rich sources of polyphenols. Antioxidant polyphenols also have many other health-promoting traits, including reducing inflammation, fighting viruses, lowering cholesterol, preventing wrinkles and supporting immune functions and vision. Cancer research is especially promising. Fruit antioxidants from grape, bilberry and choke-cherry inhibit the growth of colon cancer cells. Strawberry, blueberry and raspberry juices all inhibit cancer mutations in cells.
And fruits are a standout in cardiovascular disease prevention. According to researchers at the University of Minnesota and the University of Oslo in Norway, various flavonoid-rich foods are associated with significant mortality reduction—the more flavonoids in the diet, the less heart disease. Star foods are apples, pears, red wine, grapefruit and strawberries.
These days, scientists take fruits pretty seriously. The federal government has its “5 A Day” program, and the National Cancer Institute launched a campaign called “Savor the Spectrum,” which encourages Americans to eat fruits and vegetables from each color group (orange/yellow, red, green, white and blue-purple) every day. As a bonus, consuming five servings of fruit and vegetables daily provides 6 to 8 mg of beta-carotene, a fat-soluble antioxidant.
As nutritional powerhouses, berries lead the pack. Though small in stature, they make up for it as conceivably the most concentrated sources of beneficial phytochemicals. For sheer antioxidant power, berries are your best bet.
North American cranberry (Vaccinium macrocarpon) is the first fruit in world to carry a health claim, which was approved by the French Food Safety Agency. It states that consumption of certain amounts of the fruit can “help reduce the adhesion of certain E. coli bacteria to the urinary tract walls.” This is the explanation for cranberry’s use in preventing urinary tract infections (UTIs).
In a 2004 study from the United Kingdom, cranberry was shown to reduce the number of symptomatic UTIs over a 12-month period. To carry the claim, supplements must contain at least 36 mg of proanthocyanidins.
Cranberry also reduces kidney stone formation and periodontal disease. Other likely future claims will focus on prevention of stomach ulcers, mouth bacteria and plaque.
Scientists in Taiwan found that proanthocyanidin A-1 from Alpine cranberries (Vaccinium vitis-idaea, a lingonberry bush) suppressed the attachment and penetration of the herpes simplex virus type 2 (HSV-2) in the test tube and disturbed the late stage of HSV-2 infection.
Blueberry (Vaccinium angustifolium, V. corymbosum and V. pallidum) is the brain berry, says James A. Joseph, a lead scientist at the U.S. Department of Agriculture Human Nutrition Center on Aging. In one series of experiments in rats, Joseph mimicked the oxidative damage that goes along with brain aging. Normal rats seemed to age overnight, but rats who had feasted on blueberries had no damage at all. Some elderly blueberry-fed rats showed actual improvements on cognitive and motor-skills tests. Mexican scientists also found that blueberry significantly improved memory in aged rats.
Blueberries also might be protective against or reverse neurodegenerative disorders, including neuronal aging and Alzheimer’s disease. A study conducted at the University of Guelph in Canada says that blueberry antioxidants help protect the brain and central nervous system. Another Canadian paper reported that consumption of lowbush blueberries (V. angustifolium) helped guard neurons against prolonged stroke-induced damage. In a Tufts University study, blueberries enhanced brain cell signaling associated with memory and apparently defeated genetic predisposition to Alzheimer’s disease.
The USDA claims that blueberries can lower cholesterol as effectively as a commercial drug (ciprofibrate).
Blueberries also can help fight against cancer. Another compound, pterostilbene, possesses similar cancer-preventive qualities to those found in resveratrol from grapes. Pterostilbene reduces colon cancer by 57 percent and has been shown to inhibit liver cancer.
Bilberry (Vaccinium myrtillus), a European relative of cranberry and blueberry, has become a popular supplement in the United States for its vision-improving benefits. The anthocyanidins found in bilberry include cyanidin, delphinidin, petunidin, malvidin and pelargonin. Standardized bilberry fruit extract can reduce age-related macular degeneration risk and helps to recover reduced visual function caused by overuse, improving such symptoms as vision with sparks; dim vision; and eye fatigue in computer operators, office workers and students.
A recent Finnish paper concludes that berry antioxidants, especially ellagitannins, abundant in raspberry (Rubus idaeus), are strong antibacterial agents. The scientists concluded, “Antimicrobial berry compounds may have important applications in the future as natural antimicrobial agents for the food industry as well as for medicine.”
Raspberries and their relatives also might help ward off cancer. In 2001, microbiologist Lyndon Larcom of the University of Mississippi completed a series of test-tube studies indicating that both strawberries and raspberries can block several types of carcinogens.
A series of clinical findings at Hollings Cancer Center at the Medical University of South Carolina substantiate that one daily cup of red raspberries slows the growth of abnormal colon cells and prevents the development of cells infected with human papilloma virus, a cause of cervical cancer. The compound responsible is ellagic acid, which recent research has confirmed to be an effective antimutagen and anticarcinogen, with antibacterial and antiviral properties. Red raspberries are the highest source of ellagic acid yet discovered, with more than twice as much as strawberries and more than 10 times as much as cranberries, two other relatively rich sources.
Black raspberries were once reserved for making purple dye—the kind used to stamp meat “USDA APPROVED.” Besides being a largely undiscovered delicious fruit, they now are known to have some stunning antioxidant properties. Biologist Gary Stoner of Ohio State University published work showing that these tasty berries inhibited cancer of the colon, mouth and esophagus. One study showed a 60 to 80 percent reduction in colon tumors in rats fed high levels of black raspberries. The fruit, at only 5 percent of the rats’ diet, reduced the oral cancers by about half.
An extract of the closely related blackberry (Rubus spp.) prevented circulatory failure and multiple organ dysfunction in rats with blood poisoning.
Grapes have been at the forefront of the interest in fruit antioxidants. In a study of red grape seed proanthocyanidins, 100 mg of proanthocyanidins per kg of body weight reduced free radical activity by 75 percent in rats. These often are used to treat arthritis and other inflammatory conditions. A research review of grape seed found that oral use decreased plasma total and LDL cholesterol in subjects with high cholesterol.
Resveratrol, a grape antioxidant with cardioprotective effects, accounts for 5 percent to 10 percent of grape skin biomass. It has been found to inhibit each stage of multistage carcinogenesis, specifically prostate cancer.
One fresh apple has the antioxidant zap of 1,500 milligrams of vitamin C, a dose more than 37 times higher than the recommended daily allowance. The Journal of Agriculture and Food Chemistry says, “The high content of phenolic compounds, antioxidant activity, and antiproliferative activity of apple peels indicate that they may impart health benefits when consumed and should be regarded as a valuable source of antioxidants.”
An apple a day keeps senility away. A study out of the Journal of Agricultural and Food Chemistry indicates that quercetin from apples can help prevent oxidative stress in the brain and, in turn, might help prevent Alzheimer’s disease. The researchers tested quercetin and vitamin C for protecting poisoned nerve cells. Compared with vitamin C, quercetin produced greater protection at lower concentrations.
Researchers at the University of California, Davis, School of Medicine say that drinking apple juice and eating apples has a valuable effect on heart disease risk factors. Compounds in the fruit and juice act like red wine and tea to slow the oxidation of LDL cholesterol. When LDL oxidizes, plaque accumulates, causing atherosclerosis.
Sour cherries (Prunus cerasus), also called tart cherries, contain high levels of anthocyanins that are strong antioxidants and anti-inflammatories. They are becoming popular treatments for arthritis. Sour cherries are available fresh in season in the upper Midwest and Pacific Northwest, and are available canned nationwide.
Even humble oranges and grapefruits get into the act. The citrus flavonoids hesperidin and naringin cut cholesterol levels by about 25 percent in lab animals.
Juicy watermelon, already packed with antioxidants, is an excellent source of the essential amino acid citrulline, which the body uses to make arginine, another important amino acid needed for heart and immune health. Arginine is a precursor for nitric oxide, which lowers blood pressure, reduces blood clotting and protects against heart attack and stroke. In a 2007 study, drinking watermelon juice with every meal for three weeks boosted blood arginine levels by 22 percent.
The produce shelf is crowded with a whole new palette of international tropical delights. From acai to star fruit, these trendy fruits pack a wallop of life-extending flavonoids. Many of these fruits have great reputations worldwide for their health effects, and science is hot on the trail of verifying the claims.
Pomegranate (Punica granatum) is a top antioxidant that has caught fire with Americans. The juice of the pomegranate measures in at three times the antioxidant activity of other antioxidant-rich foods, such as red wine or green tea. It’s been linked to improved heart health, and there is evidence that pomegranate could protect against prostate cancer and slow cartilage loss in arthritis. Showing promise for weight control, an extract of the leaves suppressed appetite and reduced food intake for high-fat diets.
Acai (Euterpe oleracea), the berry from an Amazon palm, is thought to have the highest antioxidant value of any food, thanks to a high level of anthocyanins. Researchers believe acai, a small, round, blackish-purple fruit (also called Amazonian palm berry) has five times more antioxidants than blueberry. Acai is becoming increasingly available in beverage form at health-food stores.
Camu-camu (Myrciaria dubia) is a fruit native to the Brazilian and Peruvian Amazon. The dark-red fruit is a very good source of vitamin C (ascorbic acid), with 40 to 100 times more vitamin C than oranges and four to 20 times more than acerola, both of which are excellent sources in their own right. According to scientists in Brazil, 100 grams of the ripe fruit has a whopping 5 grams of vitamin C, so you could get very large doses in a small glass of the tasty juice. Folk uses of camu-camu include fortifying the immune system, increasing energy and vitality, strengthening the nervous system, promoting white cell production, detoxification through the liver and increasing cardiovascular function. Camu-camu is available at health-food stores as a supplement or juice.
Star fruit (Averrhoa carambola), also known as carambola, is grown extensively in the tropics, from Southeast Asia to Florida. The delicious treat is rich in antioxidants, especially proanthocyanidins and epicatechin, more commonly associated with green tea.
We will soon be hearing a lot more about the Oxygen Radical Absorbance Capacity (ORAC) testing system, which measures antioxidant capability. Look for ORAC values to appear soon on food packages, giving the consumer a tool to compare antioxidant benefits from one product to another.
The National Research Council has recommended consumption of five fruit and vegetable servings daily. A total of 1,670 ORAC units would be the average equivalent of eating five mixed servings of fruits and vegetables a day. However, surveys find that only 5 percent of the U.S. population consumes their five daily servings. And the USDA estimates average flavonoid consumption at between 23 mg and 1,000 mg per day—a pretty wide spread. If we concentrate on fruits and vegetables with a high antioxidant capacity for the five servings, we can achieve ORAC intakes as high as 6,000 to 7,000 units.
The USDA Food Guide Pyramid recommends five to nine servings of produce daily. If one of those servings is a dark fruit or berry, you’re probably in good shape, antioxidant-wise.
Smoothies taste terrific, are easy to make and are a great way to add more fruit to your diet. If you’re trying to incorporate more berries, smoothies are the perfect choice—all berries taste great in smoothies and shakes. Try one of the following recipes, or make up your own.
Recipe source: Crocker, Pat. The Smoothies Bible. Toronto, Ontario: Robert Rose, 2003.
Recipe source: Lana, Wai. Wai Lana’s Favorite Juices. Malibu, California: Wai Lana Productions, 2003.
Karta Purkh Singh Khalsa is a health educator who lives in Eugene, Oregon. His newest book, The Way of Ayurvedic Herbs (Lotus Press), is soon to be released.
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