Phytonutrients or phytochemicals are potentially used as “chemoprotective agents” for a number of human diseases. Nearly 50,000 species of higher plants have been used for medicinal purposes. Use of plants ranges from crude preparations or extracts to refined extracts (whole or part of plants) and single molecular species. Some well known herbal remedies are obtained from cranberry, Echinacea, feverfew, garlic, Ginkgo biloba, St. John’s wart, saw palmetto etc. Some notable bioactive compounds used as drugs include digoxin, digitoxin, morphine, reserpine, Taxol, vinblastine and vincristine. Some 80% of the world’s population still relies upon plants for primary health care. About 25% of prescription medicines are still derived either directly or indirectly from plants (Farnsworth and Soejarto, 1991). World trade in medicinal plants accounts for about 30% of the total drug market. Of the drugs prescribed in developed countries 25% derived from about 100 plant species (Comer and Debus, 1996).
Phytonutrients or phytochemicals are biologically active substances naturally produced by plants for defence mechanisms against bacteria, viruses, fungi and pest organisms. Most phytochemicals have antioxidant activity and protect plant cells against oxidative damage due to sun light and oxygen exposure. The phytochemicals give plants their colour, flavour and aroma. The term phytochemical is derived from the Greek prefix ‘fitos’ meaning plant. These naturally occurring organic components of plants have physiological effects on human beings. These phytochemicals are rich in fruits, vegetables, beans, legumes, whole grains, herbs, spices and nuts. It is estimated that there are tens of thousands of phytochemicals have been identified. However only about 1000 of these were identified and only about a 100 were actually analyzed and tested. Unlike the essential nutrients (proteins, carbohydrates, fats, minerals and vitamins) that needed for growth and metabolism and other body functions, phytonutrients are considered non-essential nutrients. These non-nutritive plant chemicals are not required by the human body for sustaining life. However epidemiological studies suggest that consumption of a diet rich in fruits and vegetables is associated with a reduced risk of chronic diseases.
Antioxidant activity – The consumption of certain phytonutrients reduce the risk of cancer by neutralizing free radicals or reactive oxygen species (ROS) or oxidants responsible for the onset of diseases. The phytonutrients with antioxidant activity include allyl sulphides (onions, garlic), carotenoids (fruits, carrots), flavonoids (fruits, vegetables) and polyphenols (tea, grape fruits).
Hormonal action – Isoflavones (phytoestrogens in soybeans) act like human estrogens and help to reduce menopausal symptoms and osteoporosis (porous bones).
Enzyme stimulants – Indoles (cabbage) stimulate enzymes that lower the activity of estrogens and reduce the risk of breast cancer. The protease inhibitors are found in soy and beans and terepenes in citrus fruits and cherries.
DNA protectors – saponins (beans) interfere with DNA replication thereby preventing the multiplication of cancer cells. Caposaicin found in hot peppers protect DNA from carcinogens.
Antibacterial action – allicin (garlic) has antibacterial properties.
Anti-adhesion action – proanthocyanidins (cranberry) prevent bacterial adhesion human cells.
Cholesterol control – Phytosterols regulate the cholesterol uptake in the intestine.
The phytonutrients are readily available to human body after ingestion. Flavonoids are water –soluble and carotenoids are fat-soluble phytonutrients. The absorption of carotenoids needs the presence of good fats in the intestine. Certain phytonutrients act as antioxidants, scavenge free radicals, and inhibit cell death or apoptosis.
Disease -preventive benefits1. Reduce oxidative damage to the cells.
2. Facilitate cell-to-cell communication.
3. Stimulate detoxification enzymes and prevent dietary substances becoming carcinogenic.
4. Enhance the immune response.
5. Reduce inflammation.
6. Prevent DNA damage and aid DNA repair.
7. Modify cellular uptake of hormones.
8. Help prevent cardiovascular and eye diseases.
9. Help prevent various forms of cancer.
10. Act as antibacterial or antiviral or anti-aging agents.
Kinds of phytonutrients
There are many types of phytonutrients; some of the best known ones are chlorophyll, carotenoids, flavonoids and organosulfur compounds.
Chlorophyll is a chemoprotein found in the green pigments of plants. It is related to protoheme, the red pigment of blood. Chlorophyll is an extremely healthful substance, which can be obtained from green leafy vegetables (broccoli, Brussel sprouts, cabbage, lettuce and spinach), wheat grass, alfalfa, parsley and algae (chlorella and spirulina). Chlorophyll promotes formation of haemoglobin and red blood corpuscles. Chlorophyll treats bad breath. Chlorophyll fights infections. Chlorophyll is used for constipation, detoxification and wound healing. Green vegetables high in chlorophyll content aid in loosening and cleansing colon.
Carotenoids are a group of yellow, orange, red and green plant pigments with potent antioxidant activity. They are thought to cancer – preventive properties by inhibiting abnormal cell growth. Carotenoids may play a critical role in the cardiovascular and glucose health of obese individuals. More than 600 carotenoids have been found in plants. About half of the roughly 50 carotenoids in the human diet are absorbed into blood stream. Lycopene and beta-carotene each constitute 30% of plasma carotenoids. Orange carotenoids include alpha, beta and gamma carotenes. Red carotenoids constitute lycophene and astaxanthin. Yellow carotenoids are lutein and zeaxanthin.
Flavonoids are the most diverse and best studied group of phytochemicals. They are water –soluble phytochemicals and some of which have red, blue and purple pigments. In fact more than 6000 flavonoids that occur in plants have been described. The main subclasses include catechins, flavonols, flavanones, flavones and Isoflavones (phytoestrogens). Out of all the phytochemicals in fruits and vegetables, it is the flavonoids that we eat in large quantity in our diet. Flavonoids act as antioxidants, protect cholesterol from oxidation to unsafe cholesterol oxides, inhibit the formation of blood clots and have anti-inflammatory and antitumor action. One study found that men with the highest consumption of flavonoids had 60% less mortality from heart disease and 70% lower risk of stroke than the low flavonoids consumer. Consumption of flavonoids was responsible for 25% of the difference in mortality rates in a study conducted in 7 –European countries(UC Davis report).
Organosuphur compounds (isothiocyanates) are found in the allium and brassica vegetables. Isothiocyanates originate as glucosinolates in plants and are converted into isothiocyanates by the enzyme myrosinase. Allium vegetables include garlic, leeks, onion, and shallouts.They contain flavonoids, vitamin C and selenium. They have been shown to have cancer protective and cardioprotective properties. Brassica vegetables include broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, kale and watercress. They also contain flavonoids and vitamin C. They are protective agents for many forms of cancer. Sulphur compounds are also found in grains, wheat germs, oat meal and in fruits like figs, plantain, papaya and pine apple.