Wednesday, November 25, 2009
Thursday, November 5, 2009
Phytonutrient - Flavonoids
flavonoids
What can high-flavonoid foods do for you?
Help protect blood vessels from rupture or leakage
Enhance the power of your vitamin C
Protect cells from oxygen damage
Prevent excessive inflammation throughout your body
What events can indicate a need for more high-flavonoid foods?
Easy bruising
Frequent nose bleeds
Excessive swelling after injury
Frequent colds or infections
Sources of flavonoids include: apples, apricots, blueberries, pears, raspberries, strawberries, black beans, cabbage, onions, parsley, pinto beans, and tomatoes.
Description
What are flavonoids?
Flavonoids, an amazing array of over 6,000 different substances found in virtually all plants, are responsible for many of the plant colors that dazzle us with their brilliant shades of yellow, orange, and red.
Classified as plant pigments, flavonoids were discovered in 1938 when a Hungarian scientist named Albert Szent-Gyorgyi used the term "vitamin P" to describe them.
The chemistry of flavonoids is complicated, and within the non-technical term "flavonoids" can be found many different chemical groups of substances. These groups include flavonols, dihydroflavonols, flavones, isoflavones, flavanones, anthocyanins, and anthocyanidins. Within each of these groups fall hundreds, and sometimes thousands of different flavonoids.
For example, well-known flavonols include quercetin, rutin, and hesperidin, while well-known flavones include apigenin and luteolin. Flavonoids may also be named directly after the unique plant that contains them. Ginkgetin is a flavonoid from the ginkgo tree, and tangeretin is a flavonoid from the tangerine.
How it Functions
What is are the functions of flavonoids?
Protection of cell structures
Most flavonoids function in the human body as antioxidants. In this capacity, they help neutralize overly reactive oxygen-containing molecules and prevent these overly reactive molecules from damaging parts of cells. Particularly in oriental medicine, plant flavonoids have been used for centuries in conjunction with their antioxidant, protective properties. Scultellaria root, cornus fruit, licorice, and green tea are examples of flavonoid-containing foods widely used in oriental medicine. While flavonoids may exert their cell structure protection through a variety of mechanisms, one of their potent effects may be through their ability to increase levels of glutathione, a powerful antioxidant, as suggested by various research studies.
Vitamin C support
The relationship between flavonoids and vitamin C was actually discovered by mistake. Dr. Albert Szent-Gyorgyi, the Nobel Prize winning researcher who discovered flavonoids, was attempting to make a preparation of vitamin C for one of his patients with blood vessel problems. The preparation he gave the patient was not 100% pure - it contained other substances along with the vitamin C. It worked amazingly well.
Later, when Dr. Szent-Gyorgyi purchased a pure solution of vitamin C, he found it was not nearly so effective with his patient. He suspected flavonoids as the magic addition to vitamin C in his first impure preparation. Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.
Inflammation control
Inflammation - the body's natural response to danger or damage - must always be carefully regulated to prevent overactivation of the immune system and unwanted immune response. Many types of cells involved with the immune system - including T cells, B cells, NK cells, mast cells, and neutrophils - have been shown to alter their behavior in the presence of flavonoids. Prevention of excessive inflammation appear to be a key role played by many different chemical categories of flavonoids.
Antibiotic activity
In some cases, flavonoids can act directly as antibiotics by disrupting the function of microorganisms like viruses or bacteria. The antiviral function of flavonoids has been demonstrated with the HIV virus, and also with HSV-1, a herpes simplex virus.
Deficiency Symptoms
What are deficiency symptoms for flavonoids?
Excessive bruisability, nose bleeds, swelling after injury, and hemorrhoids can be indicators of flavonoid deficiency. Generally weakened immune function, as evidenced by frequent colds or infections, can also be a sign of inadequate dietary intake of flavonoids.
Toxicity Symptoms
What are toxicity symptoms for flavonoids?
Even in very high amounts (for example, 140 grams per day), flavonoids do not appear to cause unwanted side effects. Even when raised to the level of 10% of total caloric intake, flavonoid supplementation has been shown non-toxic. Studies during pregnancy have also failed to show problems with high-level intake of flavonoids.
Impact of Cooking, Storage and Processing
How do cooking, storage, or processing affect flavonoids?
Heat, degree of acidity (pH), and degree of processing can have a dramatic impact on the flavonoid content of food. For example, in fresh cut spinach, boiling extracts 50% of the total flavonoid content.
With onions (a less delicate food), boiling still removes about 30% of the flavonoids (and specifically, a group of flavonoids called the quercitin glycosides). Overcooking of vegetables has particularly problematic effects on this category of nutrients.
Factors that Affect Function
What factors might contribute to a deficiency of flavonoids?
Poor intake of fruits and vegetables - or routine intake of high-processed fruits and vegetables - are common contributing factors to flavonoid deficiency. It is difficult to overemphasize the impact of processing and a non-whole foods diet on flavonoid intake. If the pulpy, fibrous parts of fruits are eliminated from the juice, and the vibrant natural colors of canned vegetables are lost during repeated heating, risk of flavonoid deficiency is greatly increased.
Drug-Nutrient Interactions
What medications affect flavonoids?
The impact of prescription medicines on flavonoid status is not well studied. However, in an interesting twist when looking from the other direction at the impact of flavonoids on drug status, researchers have discovered that a flavonoid in grapefruit juice called naringin can increase the absorption of certain heart-related drugs (including nifedipine, felodipine and verapamil), as well as the antihistamine terfenadine.
Nutrient Interactions
How do other nutrients interact with flavonoids?
Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.
Health Conditions
What health conditions require special emphasis on flavonoids?
Flavonoids may play a role in the prevention and/or treatment of the following health conditions:
Allergy
Asthma
Atopic dermatitis
Candida infection
Cataracts
Diabetes
Gout
Hemorrhoids
Macular degeneration
Migraine
Periodontal disease
Stomach ulcer
Varicose veins
Form in Dietary Supplements
What forms of flavonoids are found in dietary supplements?
By far the most common supplemental form of flavonoids are the citrus flavonoids quercetin, rutin, and hesperidin. Of these three, the most common is quercetin.
Doses in commonly sold supplements usually range from 25-200 milligrams, although clinical studies using flavonoids often use much higher level interventions in the 500-3,000 milligram range.
It is not difficult to reach the 1,000-milligram range from dietary intake, if the diet contains an adequate amount of whole, properly prepared fruits and vegetables.
Food Sources
What foods provide flavonoids?
Virtually all fruits, vegetables, herbs and spices contain flavonoids. They are also found in other types of food, including dry beans (where they give red beans,black beans, and speckled beans their color) and grains (where the color provided by flavonoids is usually in the yellow family). Products made from the foods above (for example, wines made from grapes) also typically contain a wide variety of flavonoids.
While the flavonoid family is too complex to report all of its food connections, some highlights are especially important. In the fruit family, it is berries that come out highest in the chemical category of flavonoids called anthocyanins. Black raspberries, for example, may contain up to 100 milligrams of anthocyanins per ounce.
Green tea has flavonoid components called catechins that may reach 1,000 milligrams (or 1 gram) per cup. In general the more colorful components of the food - like the skins of fruits - contain the highest concentration of flavonoids. An exception to this rule, however, is the white pulpy inside of oranges. Unlike the watery orange-colored sections of this fruit, which contain virtually all of its vitamin C, the orange's flavonoids are found in the white pulpy portion inside the skin and surrounding the sections.
Public Health Recommendations
What are current public health recommendations for flavonoids?
At present there are no public health recommendations for flavonoids.
References
Divi RL, Chang HC, Doerge DR. Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action. Biochem Pharmacol 1997;54(10):1087-1096 1997.
Gil MI, Ferreres F, Tomas-Barberan FA. Effect of postharvest storage and processing on the antioxidant constituents (flavonoids and vitamin C) of fresh-cut spinach. J Agric Food Chem 1999;47(6):2213-7 1999.
Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995 1995.
Ioku K, Aoyama Y, Tokuno A, et al. Various cooking methods and the flavonoid content in onion. J Nutr Sci Vitaminol (Tokyo) 2001;41(7): 78-83 2001.
Middleton E Jr, Kandaswami C. The impact of plant flavonoids on mammalian biology: implications for immunity, inflammation and cancer. Chapter 15 in: Harbourne JB (Ed). The flavonoids: advances in research since 1986. Chapman & Hall, London, 1993; 61... .
Middleton E, Kandaswami C. Effects of flavonoids on immune and inflammatory cell functions. Biochem Pharmacol 1992;43(6):1167-1179 1992.
Minato K, Miyake Y, Fukumoto S et al. Lemon flavonoid, eriocitrin, suppresses exercise-induced oxidative damage in rat liver. Life Sci 2003 Feb 21;72(14):1609-16 2003.
Myhrstad MC, Carlsen H, Nordstrom O et al. Flavonoids increase the intracellular glutathione level by transactivation of the gamma-glutamylcysteine synthetase catalytical subunit promoter. Free Radic Biol Med 2002 Mar 1;32(5):386-93 2002.
Okuda T, Yoshida T, Hatano T. Antioxidant phenolics in oriental medicine. In: Yagi K. (Ed). Active oxygens, lipid peroxides, and antioxidants. Japan Sci Soc Press, Tokyo, 1993;333-346 1993.
Panthong A, Kanjanapothi D, Tuntiwachwuttikul P, et al. Antiinflammatory activity of flavonoids. Phytomedicine 1994;1:141-144 1994.
Roger CR. The nutritional incidence of flavonoids: some physiologic and metabolic considerations. Experientia 1988;44(9):725-804 1988.
Tarayre JP, Lauressergues H. Advantages of a combination of proteolytic enzymes, flavonoids, and ascorbic acid in comparison with non-steroidal anti-inflammatory agents. Arznein-Forsch 1977;27:1144-1149 1977.
carotenoids
carotenoids
What can high-carotenoid foods do for you?
Protect your cells from the damaging effects of free radicals
Provide a source of vitamin A
Enhance the functioning of your immune system
Help your reproductive system function properly
What events and lifestyle factors can indicate a need for more high-carotenoid foods?
Smoking and regular alcohol consumption
Low intake of fruits and vegetables
Food sources of carotenoids include carrots, sweet potatoes, spinach, kale, collard greens, and tomatoes. To maximize the availability of the carotenoids in the foods listed above, the foods should be eaten raw or steamed lightly.
Description
What are carotenoids?
Carotenoids represent one of the most widespread groups of naturally occurring pigments. These compounds are largely responsible for the red, yellow, and orange color of fruits and vegetables, and are also found in many dark green vegetables. The most abundant carotenoids in the North American diet are beta-carotene, alpha-carotene, gamma-carotene, lycopene, lutein, beta-crpytoxanthin, zeaxanthin, and astaxanthin.
How it Functions
What are the functions of carotenoids?
Preventing Vitamin A Deficiency
Until late in the 20th Century, the functions of carotenoids were discussed only in terms of their potential vitamin A activity. Certain members of the carotenoid family, approximately 50 carotenoids of the known 600, are called "provitamin A" compounds because the body can convert them into retinol, an active form of vitamin A.
As a result, foods that contain carotenoids can help prevent vitamin A deficiency. The most commonly consumed provitamin A carotenoids are beta-carotene, alpha-carotene, and beta-cryptoxanthin, but gamma-carotene and beta-zeacarotene also have provitamin A activity.
Antioxidant & Immune-Enhancing Activity
In recent years, carotenoids have received a tremendous amount of attention as potential anti-cancer and anti-aging compounds. Carotenoids are powerful antioxidants, protecting the cells of the body from damage caused by free radicals. Carotenoids, and specifically beta-carotene, are also believed to enhance the function of the immune system.
Promoting Proper Cell Communication
In addition to their antioxidant and immune-enhancing activity, carotenoids have shown the ability to stimulate cell to cell communication. Researchers now believe that poor communication between cells may be one of the causes of the overgrowth of cells, a condition which eventually leads to cancer. By promoting proper communication between cells, carotenoids may play a role in cancer prevention.
It is also believed that carotenoids participate in female reproduction. Although the exact function of carotenoids in female reproduction has not yet been identified, it is known that the corpus luteum has the highest concentration of beta-carotene of any organ in the body, suggesting that this nutrient plays an important role in reproductive processes.
Deficiency Symptoms
What are deficiency symptoms for carotenoids?
A low dietary intake of carotenoids is not known to directly cause any diseases or health conditions, at least in the short term. However, if your intake of vitamin A is also low, a dietary deficiency of the provitamin A carotenoids (beta-carotene, alpha-carotene, and beta-cryptoxanthin) can cause the symptoms associated with vitamin A deficiency.
In addition, long-term inadequate intake of carotenoids is associated with chronic disease, including heart disease and various cancers. One important mechanism for this carotenoid-disease relationship appears to be free radicals. Research indicates that diets low in carotenoids can increase the body's susceptibility to damage from free radicals. As a result, over the long term, carotenoid-deficient diets may increase tissue damage from free radical activity, and increase risk of chronic diseases like heart disease and cancers.
Due to low consumption of fruits and vegetables, many adolescents and young adults do not take in enough carotenoids. In addition, if you smoke cigarettes and/or drink alcohol, you may have lower than normal blood levels of carotenoids. Statistically speaking, smokers and drinkers eat fewer foods that contain carotenoids. Also, researchers suspect that cigarette smoke destroys carotenoids. However, if you do smoke or drink, use carotenoid supplements with caution (see Toxicity section).
Toxicity Symptoms
What are toxicity symptoms for carotenes?
A tell-tale sign of excessive consumption of beta-carotene is a yellowish discoloration of the skin, most often occurring in the palms of the hands and soles of the feet. This condition is called carotenodermia, and is reversible and harmless. Excessive consumption of lycopene can cause a deep orange discoloration of the skin. Like carotenodermia, lycopenodermia is harmless.
High intake of carotenoid-containing foods or supplements is not associated with any toxic side effects. As a result, the Institute of Medicine at the National Academy of Sciences did not establish a Tolerable Upper Intake Level (UL) for carotenoids when it reviewed these compounds in 2000.
However, the results of two research studies indicate that those who smoke heavily and drink alcohol regularly, may increase their chance of developing lung cancer and/or heart disease if they take beta-carotene supplements in amounts greater than 20-30 milligrams per day.
Impact of Cooking, Storage and Processing
How do cooking, storage, or processing affect carotenoids?
In certain cases, cooking can improve the availability of carotenoids in foods. For example, the availability of lycopene from tomato products is increased when the foods are processed at high temperatures. As a result, your body absorbs the lycopene in canned, pasteurized tomato juice more easily than the lycopene in a fresh tomato. In addition, lightly steaming carrots and spinach improves your body's ability to absorb the carotenoids in these foods.
It is important to note, however, that in most cases, prolonged cooking of vegetables decreases the availability of carotenoids by changing the shape of the carotenoid from its natural trans-configuration to a cis-configuration. For example, fresh carrots contain 100% all-trans beta-carotene, while canned carrots contain only 73% all-trans beta-carotene.
Factors that Affect Function
What factors might contribute to a deficiency of carotenoids?
Carotenoids are fat-soluble substances, and as such require the presence of dietary fat for proper absorption through the digestive tract. Consequently, your carotenoid status may be impaired by a diet that is extremely low in fat or if you have a medical condition that causes a reduction in the ability to absorb dietary fat such as pancreatic enzyme deficiency, Crohn's disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease.
Drug-Nutrient Interactions
What medications affect carotenoids?
The cholesterol-lowering medications referred to as bile acid sequestrants (Cholestyramine, Colestipol, and Colestid) lower blood levels of carotenoids. In addition, margarines enriched with plant sterols such as Benecol and Take Control, may decrease the absorption of carotenoids. Olestra, a fat substitute added to snack foods, may also decrease the absorption of carotenoids.
Nutrient Interactions
How do other nutrients interact with carotenoids?
Beta-carotene supplements reduce blood levels of lutein, suggesting that carotenoids may compete with each other for absorption.
Supplementing your diet with pectin may decrease the absorption of carotenoids.
Health Conditions
What health conditions require special emphasis on carotenoids?
Carotenoids may play a role in the prevention and/or treatment of the following health conditions:
Acquired Immunodeficiency Syndrome (AIDS)
Age-related macular degeneration
Angina pectoris
Asthma
Cataracts
Cervical cancer
Cervical dysplasia
Chlamydial infection
Heart disease
Laryngeal cancer (cancer of the larynx)
Lung cancer
Male and female infertility
Osteoarthritis
Photosensitivity
Pneumonia
Prostate cancer
Rheumatoid arthritis
Skin cancer
Vaginal candidiasis
Form in Dietary Supplements
What forms of carotenoids are found in dietary supplements?
In dietary supplements, carotenoids are available as synthetic all-trans beta-carotene, beta- and alpha-carotene from the algae Dunaliella, and mixed carotenes from palm oil.
It is important to note, however, that, due to the inconsistent results from research studies aimed at evaluating the health benefits of beta-carotene supplements, the National Academy of Sciences cautions against taking high dose carotenoid supplements, except as a method for preventing vitamin A deficiency.
Food Sources
What foods provide carotenoids?
The orange-colored fruits and vegetables including carrots, apricots, mangoes, squash, and sweet potatoes contain significant amounts of beta-carotene, alpha-carotene, and beta-cryptoxanthin.
Green vegetables, especially spinach, kale, and collard greens, also contain beta-carotene, and are the best sources of lutein.
Lycopene is found in tomatoes, guava, and pink grapefruit. Salmon, shellfish, milk, and egg yolks also provide carotenoids.
The contribution of spices to available carotenoids in the U.S. diet has increased steadily, making spices a great choice for upping your carotenoid intake. Cayenne pepper and chili pepper are worthy of special mention here.
Public Health Recommendations
What are current public health recommendations for carotenoids?
To date, no recommended dietary intake levels have been established for carotenoids. In an effort to set such recommendations, the Institute of Medicine at the National Academy of Sciences reviewed the existing scientific research on carotenoids in 2000.
Despite the large body of population-based research that links high consumption of foods containing beta-carotene and other carotenoids with a reduced risk of several chronic diseases, the Institute of Medicine concluded that this evidence was not strong enough to support a required carotenoid intake level because it is not yet known if the health benefits associated with carotenoid-containing foods are due to the carotenoids or to some other substance in the food.
However, the National Academy of Sciences supports the recommendations of various health agencies, which encourage individuals to consume five or more servings of fruits and vegetable every day. This level of intake of fruits and vegetables provides approximately three to six milligrams of beta-carotene.
References
Agarwal S, Rao AV. Carotenoids and chronic diseases. Drug Metabol Drug Interact 2000;17(1-4):189-210 2000. PMID:15130.
Burri BJ. Carotenoids and gene expression. Nutrition 2000 Jul-2000 Aug 31;16(7-8):577-8 2000. PMID:15140.
Delgado-Vargas F, Jimenez AR, Paredes-Lopez O. Natural pigments: carotenoids, anthocyanins, and betalains-- characteristics, biosynthesis, processing, and stability. Crit Rev Food Sci Nutr 2000 May;40(3):173-289 2000. PMID:15150.
Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995 1995.
Handelman GJ. The evolving role of carotenoids in human biochemistry. Nutrition 2001 Oct;17(10):818-22 2001. PMID:15100.
Krinsky NI. Carotenoids as antioxidants. Nutrition 2001 Oct;17(10):815-7 2001. PMID:15110.
Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000 2000.
Pizzorno J, Murray M. The Textbook of Natural Medicine. The Textbook of Natural Medicine 1998.
Young AJ, Lowe GM. Antioxidant and prooxidant properties of carotenoids. Arch Biochem Biophys 2001 Jan 1;385(1):20-7 2001. PMID:15120.
Monday, November 2, 2009
Phytonutrient
- What are phytonutrients and where are they found?
- What are the major classes of phytonutrients?
- How do phytonutrients protect against diseases?
- What is the evidence that fruit and vegetable consumption protects human health?
- Are Americans eating enough fruits and vegetables?
- What is the present state of phytonutrient research?
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1. What are phytonutrients and where are they found?
3. How do phytonutrients protect against disease?
The term "phyto" originated from a Greek word meaning plant. Phytonutrients are certain organic components of plants, and these components are thought to promote human health. Fruits, vegetables, grains, legumes, nuts and teas are rich sources of phytonutrients. Unlike the traditional nutrients (protein, fat, vitamins, minerals), phytonutrients are not "essential" for life, so some people prefer the term "phytochemical".
2. What are the Major Classes of Phytonutrients?
Some of the common classes of phytonutrients include:
- Carotenoids
- Flavonoids (Polyphenols) including Isoflavones (Phytoestrogens)
- Inositol Phosphates (Phytates)
- Lignans (Phytoestrogens)
- Isothiocyanates and Indoles
- Phenols and Cyclic Compounds
- Saponins
- Sulfides and Thiols
- Terpenes
About Carotenoids
Of all the phytonutrients, we probably know the most about carotenoids, the red, orange and yellow pigments in fruits and vegetables. The carotenoids most commonly found in vegetables (and in plasma) are listed below along with common sources of these compounds. Fruits and vegetables that are high in carotenoids appear to protect humans against certain cancers, heart disease and age related macular degeneration.
Carotenoid
Common Food Source:
- alpha-carotene - carrots
- beta-carotene - leafy green and yellow vegetables (eg broccoli, sweet potato, pumpkin, carrots)
- beta-cryptoxanthin - citrus, peaches, apricots
- lutein - leafy greens such as kale, spinach, turnip greens
- lycopene - tomato products, pink grapefruit, watermelon, guava
- zeaxanthin - green vegetables, eggs, citrus
For a more detailed discussion of carotenoid content of fruits and vegetables see Chug-Ahuja et al, Journal of the American Dietetic Association, 1993;93:318 and Mangels et al. Journal of the American Dietetic Association, 1993;93:284-296. For carotenoid values of specific foods see the USDA-NCC Carotenoid Database for U.S. Foods on the website of the Nutrient Database Laboratory.
About Polyphenols
Polyphenolic compounds are natural components of a wide variety of plants; they are also known as secondary plant metabolites. Food sources rich in polyphenols include onion, apple, tea, red wine, red grapes, grape juice, strawberries, raspberries, blueberries, cranberries, and certain nuts. The average polyphenol / flavonoid intake in the U.S. has not been determined with precision, in large part, because there is presently no U.S. national food database for these compounds. (USDA scientists and their colleagues are in the process of developing a database for foods rich in polyphenols.) It has been estimated that in the Dutch diet a subset of flavonoids (flavonols and flavones) provide 23 mg per day. Earlier estimates of dietary intake that approximated 650 mg per day (Kuhnau, World Review of Nutrition and Dietetics, 1976;24:117) are generally thought to be too high as the estimate was based on data that were generated by "old" (less specific) methodology. Scientists at the Food Composition Laboratory, Beltsville Human Nutrition Research Center are currently developing new methodology for the accurate measurement of polyphenols in foods.
Polyphenols can be classified as non-flavonoids and flavonoids. The flavonoids quercetin and catechins are the most extensively studied polyphenols relative to absorption and metabolism.
Nonflavonoids; Sources
- ellagic acid - strawberries, blueberries, raspberries
- coumarins
Flavonoids; Sources
- anthocyanins - fruits
- catechins - tea, wine
- flavanones - citrus
- flavones - fruits and vegetables
- flavonols - fruits, vegetables, tea, wine
- isoflavones - soybeans
The following are commonly proposed mechanisms by which phytonutrients may protect human health. More research is needed to firmly establish the mechanisms of action of the various phytochemicals.
Phytonutrients may:
- serve as antioxidants
- enhance immune response
- enhance cell-to-cell communication
- alter estrogen metabolism
- convert to vitamin A (beta-carotene is metabolized to vitamin A)
- cause cancer cells to die (apoptosis)
- repair DNA damage caused by smoking and other toxic exposures
- detoxify carcinogens through the activation of the cytocrome P450 and Phase II enzyme systems
4. What is the evidence that fruit and vegetable consumption protects human health?
Evidence that fruit and vegetable consumption protects human health is accumulating from large population (epidemiological) studies, human feeding studies, and cell culture studies. Listed below are a few selected population studies from the literature linking fruit and vegetable consumption to health. For an excellent review concerning vegetables, fruit and cancer prevention, see Steinmetz and Potter, Journal of the American Dietetic Association 1996;96:1027.
Evidence that Carotenoids are Protective
Fruit and vegetable consumption has been linked to decreased risk of stroke -- both hemorrhagic and ischemic stroke. Each increment of three daily servings of fruits and vegetables equated to a 22% decrease in risk of stroke, including transient ischemic attack (Gillman et al. Journal of the American Medical Association. 1995;273;1113).
Elderly men whose intake of dark green and deep yellow vegetable put them in the highest quartile for consumption of these vegetables had about a 46% decrease in risk of heart disease relative to men who ranked in the lowest quartile. Men in the highest quintile had about a 70% lower risk of cancer than did their counterparts in the lowest quintile. The differences in vegetable consumption between high and low intake rankings was not striking. Men in the highest quartile or quintile consumed more than two (>2.05 and >2.2) servings of dark green or deep yellow vegetable a day; those in the lowest quartile or quintile consumed less than one serving daily (<0.8 and <0.7). This suggests that small, consistent changes in vegetable consumption can make important changes in health outcomes (Gaziano et al. Annals of Epidemiology 1995;5:255 and Colditz et al. American Journal of Clinical Nutrition 1985;41:32).
Consumption of tomato products has been linked to decreased risk of prostate cancer. Men in the highest quintile for consumption of tomato products (10 or more servings a week) had about a 35% decrease in risk of prostate cancer compared to counterparts whose consumption put them in the lowest quintile (1.5 or fewer servings of tomato products a week) (Giovannucci et al. Journal of the National Cancer Institute 1995;87:1767).
People in the highest quintile for consumption of spinach or collard greens, plants high in the carotenoid lutein, had a 46% decrease in risk of age-related macular degeneration compared to those in the lowest quintile who consumed these vegetables less than once per month (Seddon et al. Journal of the American Medical Association. 1994;272:1413).
Evidence that Polyphenols are Protective
Flavonoid consumption has been linked to lower risk of heart disease in some, but not all, studies. Elderly Dutch men in the highest tertile of flavonoid intake had a risk of heart disease that was about 58% lower than that of counterparts in the lowest tertile of intake. Those in the lowest tertile consumed 19 mg or less of flavonoids per day, whereas those in the highest tertile consumed approximately 30 mg per day or more (Hertog et al. Lancet. 1993;342:1007). Similarly, Finnish subjects with the highest quartile of flavonoid intake had a risk of mortality from heart disease that was about 27% (for women) and 33% (form men) lower than that of those in the lowest quartile (Knekt et al. British Medical Journal. 1996;312:478).
However, in other studies the protective effect of flavonoids could not be confirmed. For Welch men, flavonol intake did not predict a lower rate of ischemic heart disease and was weakly positively associated with ischemic heart disease mortality (Hertog et al. American Journal of Clinical Nutrition. 1997;65:1489). For U.S. male health professionals, data did not support a strong link between intake of flavonoids and coronary heart disease (Rimm et al. Annals of Internal Medicine. 1996;125:384).
5. Are Americans Eating Enough Fruits and Vegetables?
An excellent source of information on fruit, vegetable and grain intake of Americans is USDA's 1994/96 Continuing Survey of Food Intakes by Individuals conducted by the Food Surveys Research Group, Beltsville Human Nutrition Research Center. The following information comes from that survey.
About Vegetable Intake
On average, Americans consume 3.3 servings of vegetables a day. However, dark green vegetables and deep yellow vegetables each represent only 0.2 daily servings.
On any given day, about 49% of the population consumes at least the minimum number of servings of vegetables recommended (3 servings per day); 41% consume the number of servings recommended based on caloric intake (3 servings per day for those consuming less than 2200 calories, 4 servings per day for those consuming 2200-2800 calories, 5 servings per day for those consuming 2800 calories or more). About 10% of the population consumes less than one serving of vegetable per day.
About Fruit Intake
On any given day about 29% of the population consumes at least the minimum number of servings of fruit recommended (2 servings per day); 24% consume the number of servings recommended based on caloric intake (2 servings per day for those consuming less than 2200 calories, 3 for those consuming 2800 calories, 4 for those consuming 2800 calories or more). About 48% consume less than one serving of fruit a day.
6. What is the Present Status of the Art of Phytonutrients Research?
Population studies have linked fruit and vegetable consumption with lowering the risk for chronic diseases including specific cancers and heart disease. However, media and consumer interest in phytonutrients and functional foods is far ahead of established proof that documents the health benefits of these foods or food components for humans. Phytonutrients research is experiencing remarkable growth. Hopefully, more specific information on phytonutrient consumption and human health will be forthcoming in the near future. For now, it appears that an effective strategy for reducing risk of cancer and heart disease is to increase consumption of phytonutrient-rich foods including fruits, vegetables, grains and teas.
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