We’ve heard the adages growing up, and we even tell them to our own children: “An apple a day keeps the doctor away.” “Spinach will make you strong.” “Carrots are good for your eyes.” At the time, we may not have had reasons to back these statements, but research is now showing why specific fruits and vegetables should be consumed.
Consumption of fruits and vegetables has been linked to a reduced risk of heart disease and cancer. Substantial evidence backs up these benefits, which are reflected in the various Food and Drug Administration– approved health claims related to fruits and vegetables:
“Low fat diets rich in fiber-containing grain products, fruits, and vegetables may reduce the risk of some types of cancer, a disease associated with many factors.”
“Diets low in saturated fat and cholesterol and rich in fruits, vegetables, and grain products that contain some types of dietary fiber, particularly soluble fiber, may reduce the risk of heart disease, a disease associated with many factors.”
“Low fat diets rich in fruits and vegetables (foods that are low in fat and may contain dietary fiber, vitamin A, or vitamin C) may reduce the risk of some types of cancer, a disease associated with many factors.”
In addition, in July 2003, the National Cancer Institute presented a new dietary guidance message, “Diets rich in fruits and vegetables may reduce the risk of some types of cancer and other chronic diseases.” Although it is not a health claim, FDA encourages food manufacturers to use this statement in association with those fruits, vegetables, and foods that meet the criteria established by the national 5 A Day for Better Health Program (www.5aday.gov, www.5aday.com). The program, which is jointly sponsored by NCI and the Produce for Better Health Foundation (PBH), works to increase the average consumption of fruits and vegetables to five servings every day. Excluding high-fat processed potato products, Americans are eating only about 3.6 servings of fruits and vegetables each day, according to PBH.
By not consuming enough fruits and vegetables, people are missing out on a variety of health benefits, such as memory improvement, weight management, and positive impacts on heart health and colon and prostate cancer. From A to Z (well, T in this article), there are a garden variety of fruits and vegetables that have specific health benefits. To address every single one could take as long as it would to grow and harvest these nutritional foods, so here is a sampling of recent research on specific fruits and vegetables.
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• Apples. Research from the University of Massachusetts–Lowell suggested that apple juice may protect against oxidative damage that contributes to age-related brain disorders and may help to maintain brain performance (Rogers et al., 2003).
Researchers evaluated normal adult mice as well as mice that carry a gene associated with diseases like Alzheimer’s. Groups of both types of mice were exposed to either a “complete” diet including known antioxidants or a “deficient” diet that is thought to increase oxidative damage. Some mice in each group then received apple juice concentrate in their drinking water. Other mice received sugar.
After one month, the animals were tested to determine their memory and learning capabilities. Mice who consumed the diets augmented with apple juice tended to perform better on the maze tests, and all had less oxidative brain damage than the controls. In addition, adding apple juice to the diet protected the normal mice from the oxidative damage caused by the deficient diet and protected the genetically deficient mice from both their genetic predisposition and the deficient diet.
“Our results suggest that something in apple juice appears to protect the brain against oxidative damage, and improves cognitive performance in these animals, even when we impose dietary or genetic challenges,” said Thomas B. Shea, Director of the university’s Center for Cellular Neurobiology and Neurodegeneration Research. “We think that this ‘something’ is the apple’s naturally high level of antioxidants.”
• Broccoli. Isothiocyanates (ITCs) in broccoli have been shown to aid in prostate cancer prevention. NCI recently issued a $1.7-million grant to a researcher at the University of Pittsburgh Cancer Institute to further study broccoli’s potential (University of Pittsburgh, 2003).
Shivendra Singh, Professor of Pharmacology and Urology at the university’s School of Medicine, had previously shown that ITCs were effective in suppressing growth of human prostate cancer cells, even at concentrations achieved by eating cruciferous vegetables such as broccoli.
He is currently working to further define the mechanisms by which ITCs induce cancer cell death, provide insights into the key structural relationships between ITCs and cell processes, and identify potential biomarkers that could be useful for future intervention trials.
“Clearly, what we eat has an effect on the development of diseases such as cancer,” said Singh. “However, we know little about the mechanisms by which certain edible plants like broccoli help our bodies fight prostate cancer and other diseases. Our goal with this study is to better understand the function and relationship of substances in broccoli that appear to be linked to inhibiting prostate cancer growth.”
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• Blueberries. According to the U.S. Highbush Blueberry Council (www.ushbc.org), researchers have found that blueberries rank number one in antioxidant activity when compared to 40 other fruits and vegetables. The antioxidants are believed to play a role in the health benefits of blueberries. For example, researchers at the Universidad Nacional Autónoma de Mexico (UNAM) and the University of Houston–Clear Lake (UHCL) reported at a 2003 Society for Neuroscience meeting that a blueberry-enriched antioxidant diet prevents an age-related increase in a protein (NF-kappaB) that responds to oxidative stress, a probable cause of brain aging (Society for Neuroscience, 2003).
In the study, researchers fed rats a blueberry-enriched diet. NF-kappaB levels were then assayed in five different brain regions involved in memory processes. The aged rats on the blueberry-enriched diet had lower NF-kappaB levels than aged rats fed a control data. Young control rats also had lower NF-kappaB levels than the aged control rats. “We also found that among the aged rats, the higher the NF-kappaB levels, the poorer their memory scores,” said Pilar Goyarzu, a doctoral student at UNAM.
Other blueberry benefits include disease prevention and anti-aging. For example, in-vitro studies showed that blueberry extracts inhibited cervical cancer cells and breast cancer cells (Wedge et al., 2001). In addition, blueberry extracts also suppressed mutagenesis by a direct-acting carcinogen and a metabolically activated carcinogen.
Another study demonstrated blueberries’ anti-aging properties (Joseph et al., 1999). When 19-month-old rats were fed 18.6 g of dried blueberry extract/kg of diet for 8 weeks, the diet was effective in reversing age-related deficits in several neuronal and behavioral parameters.
• Cherries. Anthocyanins are antioxidants present in cherries. On its Web site (www.cherrymkt.org), the Cherry Marketing Institute provides information on some of the latest research linking cherries to a reduced risk of colon cancer and lower plasma urate levels.
Studies at Michigan State University suggested that tart cherries may reduce the risk of colon cancer because of the anthocyanins and cyanidin in the cherry (Kang et al., 2003). Mice consuming a cherry diet, anthocyanins, or cyanidin had significantly fewer and smaller colon tumors than mice consuming the control diet. Anthocyanins and cyanidin also reduced cell growth of human colon cancer cell lines HT 29 and HCT 116. These results suggested that tart cherry anthocyanins and cyanidin may reduce the risk of colon cancer.
At the U.S. Dept. of Agriculture’s Western Human Nutrition Center at the University of California at Davis, researchers showed that women age 22–40 had lower blood uric acid levels after consuming two servings (280 g) of Bing sweet cherries after an overnight fast (Jacob et al., 2003). The decrease in plasma urate after cherry consumption supports reported anti-gout efficacy of cherries.
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• Grapefruit. The once-popular grapefruit diet has recently received some scientific backing. Researchers at Scripps Clinic, La Jolla, Calif., found that adding grapefruit and grapefruit juice to one’s diet can result in weight loss (Scripps Clinic, 2004). A 12-week study at the clinic’s Nutrition and Metabolic Research Center, led by Ken Fujioka, monitored weight and metabolic factors, such as insulin secretion, of 100 men and women. On average, participants who ate half a grapefruit with each meal lost 3.6 lb, while those who drank a serving of grapefruit juice three times a day lost 3.3 lb. Many patients in the study lost more than 10 lb.
“Our study participants maintained their daily eating habits and slightly enhanced their exercise routine; the only dietary change was the intake of Florida grapefruit and grapefruit juice,” said Fujioka. Additionally, the research indicated a physiological link between grapefruit and insulin. The researchers speculated that the chemical properties of grapefruit reduce insulin levels, which promotes weight loss.
“Our study shows grapefruit can play a vital role in overall health and wellness, and in battling America’s ever-growing obesity epidemic,” stated Fujioka. “Whether it’s the properties of grapefruit or its ability to satiate appetites, grapefruit appeared to help with weight loss and decreased insulin levels leading to better health.”
• Raisins. Raisins are a source of phenolics, which are thought to be protective antioxidants. The California Raisin Marketing Board Web site (www.calraisins.org) lists several studies showing that raisins have a positive impact on heart disease and cancer.
Research presented at the 2001 Experimental Biology conference reported that dietary fiber and other components in raisins could bind bile acids under laboratory conditions that are similar to conditions in the human intestine. According to the study conducted at the University of Maine, the binding of bile acids by dietary fiber and other components found in raisins may have a positive health impact by reducing the risk of both heart disease and cancer. Eating fibrous foods, such as raisins, binds intestinal bile acids and causes them to be excreted, stimulating the body to use its own cholesterol to replace those acids that have been eliminated. In addition, intestinal bacteria may change free bile acids in the colon into molecules that might enhance cancer growth. Binding these acids by dietary fiber helps to prevent possible harmful effects of these acids on cells in the colon.
In 2000, research presented at the Symposium on Advances in Clinical Nutrition found that eating two servings of raisins a day may help lower the risk of colon cancer. This clinical study was designed to confirm an earlier hypothesis that the combination of dietary fiber and tartaric acid in sun-dried raisins plays an important role in colon function and health. “We found a significant, positive correlation between consuming sun-dried raisins and a change in some colon cancer risk factors,” said Gene Spiller, lead study author and researcher at the Health Research and Studies Center in Los Altos, Calif.
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• Spinach. The National Institute of Standards and Technology recently confirmed that spinach is rich in the antioxidants beta-carotene and lutein (NIST, 2004). The antioxidants constitute 0.0019% and 0.0033% of the spinach by mass, respectively. Although this sounds small, spinach contains far more of the two combined than most other fruits or vegetables. Beta-carotene converts to vitamin A in the body and is needed for healthy sight, skin, and hair. Lutein is a pigment found in the retina and may help guard against eye diseases such as age-related macular degeneration.
NIST reached its conclusions after using the Standard Reference Material (SRM) 2385 that consists of small jars of slurried spinach—pure spinach that has been blanched, pureed, and passed through filter screens. Concentrations of vitamins and other constituents were measured and certified, so that “the food industry can use the SRM to validate analytical methods and provide accurate nutritional information for its products,” the group said.
• Onions. Onions contain quercetin, a flavonoid. According to the National Onion Association (www.onionsusa.org), quercetin is thought to help eliminate free radicals in the body, inhibit low-density-lipoprotein oxidation, protect and regenerate vitamin E, and inactivate the harmful effects of chelate metal ions.
The association stated that studies have shown that consumption of onions may be beneficial for reduced risk of certain diseases. Consumption of onions may prevent gastric ulcers by scavenging free radicals and by preventing growth of the ulcer-forming microorganism Helicobacter pylori. In addition to preventing gastric ulcers, University of Wisconsin-Madison researchers found that the more-pungent onions also exhibit strong anti-platelet activity. Further research is being conducted to determine the extent to which onion consumption and specific onion compounds affect the in-vivo aggregation of blood platelets.
A recent study showed that onions were a strong risk-reduction factor for prostate cancer mortality (Grant, 2004). Independent researcher William Grant looked at prostate cancer mortality rates for 32 predominantly Caucasian countries from the late 1990s. Dietary supply data were obtained from the Food and Agriculture Organization. Linear and multiple linear regression analyses were conducted for all 32 countries as well as the 20 European countries. The strongest risk-reduction factors for prostate cancer mortality were onions, other protective vegetable products (excluding alcohol, oils, and sweeteners), and solar UVB radiation. Grant concluded that his results were consistent with insulin-like growth factor-I (IGF-I) being an important risk factor for prostate cancer, and with allium family vegetables being important risk-reduction factors.
• Tomatoes. A recent meta-analysis study showed that tomato products may play a role in the prevention of prostate cancer (Etminan et al., 2004). Researchers looked at studies that included the use of tomato, tomato products, or lycopene. In addition to their findings, they concluded that further work is needed to determine the type and quantity of tomato products with respect to their role in preventing prostate cancer.
In addition to cancer, lycopene from tomatoes has been shown to decrease heart disease risk in women (Sesso et al., 2004). Results of this study showed that women with the highest amounts of lycopene in their blood had half the risk of cardiovascular disease seen in those with low levels of the carotenoid.
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• Strawberries. Several studies are underway related to strawberries and their health benefits. The California Strawberry Commission (www.calstrawberry.com) provides information on new clinical studies and preliminary results related to strawberries. For example, a clinical strawberry consumption study by Gene Spiller at the Health Research and Studies Center in Los Altos, Calif. is examining the effects of strawberries on plasma folate, C-reactive protein, homocysteine, body weight, blood lipids, bowel function, and blood pressure. Participants ate a serving of strawberries about 7 days a week. Preliminary results showed an increase in folate levels and slight decrease in C-reactive protein. These results suggest that the nutrients in strawberries may have a heart-healthy effect.
An analysis of survey data by Victor Fulgoni at Nutrition Impact LLC, Battle Creek, Mich., looked at strawberry eaters vs non-eaters and folate levels, lipids, blood pressure, and body weight. The analysis revealed that compared to non-strawberry eaters, strawberry eaters tend to have higher blood folate levels, higher intakes of potassium, vitamin C, and dietary fiber, and lower blood pressure, body weight, and homocysteine levels.
At USDA’s Jean Mayer Human Research Center at Tufts University, researchers showed that strawberries improved measures of cognitive function in animal studies. Preliminary results suggested that strawberries may improve certain measures of cognitive function.
Fruits and vegetables, being natural sources of beneficial nutrients like vitamins, antioxidants, and fiber, are in essence the ultimate functional food.
Research on benefits of fruits and vegetables continues
Scientists continue to publish research related to the benefits of general consumption of fruits and vegetables in the areas of heart health, osteoporosis, and cancer.
• Coronary Health. At the European Society of Cardiology in September 2003, researchers from the University of Athens in Greece presented a multicenter case control study involving around 2,000 people that found that risk of heart attacks and other coronary events was progressively lower as daily consumption of fruits or vegetables increased (Panagiotakos and Chrysohoou, 2003).
Those in the upper quintile of fruit consumption (five or more items each day) had 72% lower relative cardiac risk compared to those in the lowest quintile of intake (less than one item daily). Consumption of vegetables more than three days per week was associated with 70% lower relative cardiac risk compared to those who did not consume vegetables.
Another study showed that eating just 10 g of dietary fiber from fruits and cereals each day significantly lowered the risk of coronary heart disease (Pereira et al., 2004). Researchers from Harvard University found that coronary risk was 10–30% lower for each 10-g/day increment of total, cereal, or fruit fiber. They also found that associations were stronger for coronary deaths than for all events.
• Bone Health. A diet of alkaline-producing foods, including fruits, vegetables, vegetable proteins, and moderate amounts of milk can help maintain the body’s bone mineral density (Tucker et al., 1999). Researchers studied elderly men who were the original participants in the Framingham Heart Study. Results suggested that a diet high in fruits and vegetables, magnesium, and potassium may protect against bone loss in elderly men, helping to prevent osteoporosis.
• Prostate Cancer. High consumption of vegetables, especially cruciferous vegetables, was associated with a reduced risk of prostate cancer, according to a population-based, case-control study of 1,230 men under 65 years of age (Cohen et al., 2000). Using food-frequency questionnaires, the researchers found a positive association with the consumption of broccoli, cabbage, Brussels sprouts, and other cruciferous vegetables.
by LINDA MILO OHR
Contributing Editor, Chicago, Ill.
Cohen, J.H., Kristal, A.R., and Stanford, J.L. 2000. Fruit and vegetable intakes and prostate cancer risk. J. Natl. Cancer Inst. 92: 61-68.
Etminan, M., Takkouche, B., and Caamaño-Isorna, F. 2004. The role of tomato products and lycopene in the prevention of prostate cancer: A meta-analysis of observational studies. Cancer Epidemiol. Biomarkers Prevention. 13: 340-345.
Grant, W.B. 2004. A multicountry ecologic study of risk and risk reduction factors for prostate cancer mortality. Eur. Urology 45(3): 271-279.
Jacob, R.A., Spinozzi, G.M., Simon, V.A., Kelley, D.S., Prior, R.L., Hess-Pierce, B., and Kader, A.A. 2003. Consumption of cherries lowers plasma urate in healthy women. J. Nutr.133: 1826-1829.
Joseph, J.A., Shukitt-Hale, B., Denisova, N.A., Bielinski, D., Martin, A., McEwen, J.J., and Bickford, P.C. 1999. Reversals of age-related declines in neuronal signal transduction, cognitive, and motor behavioral deficits with blueberry, spinach, or strawberry dietary supplementation. J. Neurosci. 19: 8114-8121.
Kang, S.Y., Seeram, N.P., Nair, M.G., and Bourquin, L.D. Tart cherry anthocyanins inhibit tumor development in ApcMin mice and reduce proliferation of human colon cancer cells. 2003. Cancer Lett. 194(1): 13-19.
NIST. 2004. Standard Reference Material® 2385. Slurried spinach. NIST Standard Reference Materials Program, Natl. Inst. of Standards and Technology. http://ts.nist.gov/ts/htdocs/230/232/publicities/2385.htm.
Panagiotakos, D. and Chrysohoou, C. 2003. Consumption of fruits and vegetables attenuates the risk of developing acute coronary syndromes: The Cardio 2000 Study. Presented at the European Society of Cardiology meeting. www.escardio.org/VPO/2003/Mon_1_sept/Panagiotakos%202.pdf.
Pereira, M.A., O’Reilly, E., Augustsson, K., Fraser, G.E., Goldbourt, U., Heitmann, B.L., Hallmans, G., Knekt, P., Liu, S., Pietinen, P., Spiegelman, D., Stevens, J., Virtamo, J., Willett, W.C., and Ascherio, A. 2004. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch. Intern. Med. 164:.370-376.
Rogers, E.J., Milhalik, S., Ortiz, D., and Shea, T.B. 2003. Apple juice prevents oxidative stress and impaired cognitive performance caused by genetic and dietary deficiencies in mice. J. Nutr., Health Aging 7(6): 1-6.
Scripps Clinic. 2004. Grapefruit diet: Fact, not fiction. Press release, Jan. www.scrippsclinic.com/news/Article_Fulltext.cfm?ID=211.
Sesso, H.D., Buring, J.E., Norkus, E.P., and Gaziano, J.M. 2004. Plasma lycopene, other carotenoids, and the risk of cardiovascular disease in women. Am. J. Clin. Nutr. 79: 47-53.
Society for Neuroscience. 2003. Diet may improve cognition, slow aging, and help protect against cosmic radiation; also may explain why women are more prone to weight gain. Press release, Nov. http://web.sfn.org/content/AboutSfN1/NewsReleases/am2003_diet.html.
Tucker, K.L., Hannan, M.T., Chen, H., Cupples, L.A., Wilson, P.W.F., and Kiel, D.P. 1999. Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women. Am. J. Clin. Nutr. 69: 727-736.
University of Pittsburgh. 2003. University of Pittsburgh Cancer Institute researcher receives grant to study broccoli-derived chemicals for prostate cancer prevention. Press release, Dec. 22. http://newsbureau.upmc.com/UPCI/BroccoliStudy.htm.
Wedge, D.E., Meepagala, K.M., Magee, J.B., Smith, S.H., Huang, G., and Larcom, L.L. 2001. Anticarcinogenic activity of strawberry, blueberry, and raspberry extracts to breast and cervical cancer cells. J. Medicinal Food 4: 49-51.