What are Phytochemicals?
Phytochemicals are non-nutritive plant chemicals that have protective or disease-preventive properties. They occur naturally in plants (‘phyto’ means plant). The term is generally used to refer to those chemicals that are thought to have beneficial effects on health. There is growing evidence to support the health benefits of diets rich in fruits and vegetables.
Nutrition researchers estimate that there are more than four thousand phytochemicals that have been identified. Only about 150 of these have been studied in depth. It is well known that plants produce these chemicals to protect themselves, and it is in more recent times that research has shown that they can also protect humans against diseases.
Phytochemicals, unrecognised, have been used as ‘drugs’ for millennia. For example Hippocrates may have prescribed willow tree leaves to treat fever. Salicin, having anti-inflammatory and pain-relieving properties, was originally extracted from white willow tree and later synthetically produced as acetyl salicylic acid, the over-the-counter drug Asprin.
The purpose of this newsletter is to provide an overview of this increasingly complex topic.
Phytochemicals and Colour
The following is adapted from “What Colour is your Diet?” by D. Heber and S. Bowerman (Harper-Collins, 2001). This is an overview to give guidance and understanding, and not all foods that have phytochemicals are listed. Each bullet sets out the food colour, the phytochemicals and the foods.
· RED - Lycopene, phytoene, phytofluene, vitamin E.
Tomatoes and tomato products (sauces, soups, paste), vegetable juice, watermelon.
· GREEN - Catechins, glucosinolates, isothiocyanates, indole-3 carbinol, polyphenols, sinigrin, sulforaphane, folic acid.
Broccoli, Brussels sprouts, bok choy, cauliflower, cabbage, tea.
· GREEN/YELLOW - Lutein, zeaxanthin.
Avocado, collard greens, green beans, green peppers, kale, kiwi fruit, mustard greens.
· ORANGE - Alpha and beta-carotene, carotenoids, cryptoxanthin.
Apricots, butternut squash, canteloupe (rockmelon), carrots, mangos, pumpkin.
· ORANGE/YELLOW - Flavonoids, vitamin C.
Lemons, limes, nectarines, oranges and orange juice, paw paw (papaya), peaches, pineapple, tangerines, yellow grapefruit.
· RED/PURPLE - Anthocyanins, ellagic acid, flavonoids, polyphenols.
Blackberries, blueberries, cherries, cranberries, grapes and grape juice, plums, prunes, raisins, raspberries, red wine, strawberries.
· WHITE/GREEN - Allyl sulfides, allicin, alliin.
Chives, garlic, leeks, onion.
Classification of Phytochemicals
The list of phytochemicals in commonly consumed foods is vast. Www.wikipedia.org (/wiki/List_of_phytochemicals_in_food) provides a comprehensive list, and the following is a summary from that article and several other sources.
· Alkaloids: caffeine, theobromine, theophylline.
· Anthocyanins and anthocyanidins: cyanidin, malvidin, pelargonidin, peonidin.
· Carotenoids: alpha and beta-carotene, cryptoxanthin, lutein, lycopene, phytoene, phytofluene.
· Flavan-3-ols: catechins, theaflavin.
· Flavonols: gingerol, quercetin, resveratrol, rutin.
· Flavanones: hesperidin, silybin.
· Hydroxycinnamic acids: caffeic acid, chicoric acid, coumarin, ferulic acid.
· Indoles: allicin, alliin, allyl sulfides, indole-3-carbinol, isothiocyanate, piperine, sinigrin, sulforaphane.
· Isoflavones: daidzein, genistein, glycitein.
· Lignans: silymarin.
· Lipids: gamma-linolenic acid, omega-3, 6, 9, fatty acids, phytosterols, tocopherols (vitamin E).
· Monoterpenes: geraniol, limonene, perillyl alcohol.
· Organosulfides: glutathione, indole-3-carbinol, isothiocyanates, sulforaphane, thiosulfonates.
· Organic acids: oxalic acid, phytic acid, tartaric acid, anacardic acid.
· Phenolic acids: capsaicin, curcumin, ellagic acid, gallic acid, polyphenols, salicylic acid, tannic acid, vanillin.
· Protein inhibitors: protease inhibitors.
Many of the above can be classified in other ways, for example, ‘phenolic compounds’ or ‘terpenes’.
How do Phytochemicals Work?
As can be seen above, there are many phytochemicals and each works differently. There are several main mechanisms by which phytochemicals promote our health:
· Antioxidant Activity
Antioxidants are phytochemicals, vitamins, selenium and other nutrients that protect our cells from damage caused by free radicals. This is also called oxidative damage.
What are ‘free radicals’? Free radicals are formed as part of our natural metabolism but also by environmental factors including smoking, atmospheric pollution, herbicides, fungicides, pesticides and radiation. Free radicals are unstable molecules that react easily with essential molecules in our body, including DNA, fat and proteins. Free radicals are molecules which have one electron too many or one too few, and are thus unstable. Free radicals therefore try to gain stability by either taking electrons from another molecule or giving electrons to another molecule, thereby changing the chemical structure of the donor or recipient molecule. Thus when a free radical ‘attacks’ a molecule, that molecule will become a free radical itself, setting off a chain reaction which can result in the destruction of a cell.
Antioxidants have the property that enables them to neutralise free radicals, without becoming free radicals themselves. When antioxidants neutralise free radicals by receiving or donating an electron they do not become free radicals themselves because they are stable in both forms, thus preventing cellular damage. When an antioxidant neutralises a free radical it becomes inactive. Therefore we need to continuously supply our body with antioxidants.
The body also has its own inbuilt ways of minimising free radical damage. These include such chemicals as glutathione and the enzyme super oxide dysmutase (SOD).
Antioxidants can be found in most fruits and vegetables. Culinary herbs and medicinal herbs can also contain high levels of antioxidants. As a rule, dark-coloured fruits and vegetables have more antioxidants than other fruits and vegetables.
Many studies of phytochemicals have shown that those with antioxidant activity may reduce the risk of cancer, improve heart health, delay aging and reduce degenerative diseases.
Most phytochemicals have antioxidant activity. Those with high levels of antioxidant activity are allyl sulfides, carotenoids, flavonoids and polyphenols.
· Hormonal Action
Phytochemicals classified as flavonoids are found in grains, vegetables and fruits.
Isoflavones are a subgroup of flavonoids. These are also called phytoestrogens. These include daidzein, genistein and glycitein. All three of these are found in soybeans and the first two are also in alfalfa sprouts, red clover, chickpeas, peanuts and other legumes. These phytoestrogens have a very weak oestrogen-like activity. They may be beneficial in the management of menopausal symptoms and osteoporosis.
· Stimulation of Enzymes
Phytochemicals classified as indoles are found in the cruciferous vegetables such as Brussels sprouts and cabbages, as well as in garlic, horseradish, mustard and wasabi. These indoles, especially those in the cruciferous vegetables (for example sulforaphane), stimulate enzymes that help to protect against cancer.
Other phytochemicals which modify enzymes are protease inhibitors (found in soybeans, legumes and potatoes) and terpenes such as limonene (in citrus fruits, cherries, spearmint).
· Effect on DNA Replication
Phytochemicals classified as saponins, as found in alfalfa, beans, legumes and soybeans, interfere with the replication of cell DNA, thereby preventing the multiplication of cancer cells.
Capsaicin, a phenolic acid, is found in chilli or hot peppers, and protects DNA from carcinogens.
· Anti-bacterial Effect
The phytochemicals allicin and alliin in garlic are responsible for the anti-bacterial and anti-viral properties of this food.
· Physical Action
Some phytochemicals bind physically to cell walls, thereby preventing the adhesion of pathogens to human cell walls. The phytochemicals classified as anthocyanins are responsible for the anti-adhesion properties of cranberry. Consumption of cranberries will reduce the risk of urinary tract infections and can be helpful in their treatment, and it will also improve dental health.
Anthocyanins are also found in red wines and red/purple fruits.
Some phytochemicals with physiological properties may be elements rather than complex organic molecules. For example selenium, found in many fruits and vegetables, is involved with major metabolic pathways, including thyroid hormone metabolism and immune function. Particularly, it is an essential nutrient and cofactor for the enzymatic synthesis of glutathione, an endogenous antioxidant (ie an antioxidant produced naturally by the body).
In my March 2008 newsletter Prevention of Cancer, the diet recommended is essentially vegetarian with a strong emphasis on the intake of fruits and vegetables. This same emphasis on fruits and vegetables is in my book How to Live to 100+Years Free from Symptoms and Disease (see homepage).
Some research scientists believe that you can reduce your cancer risk by as much as 40% by eating more fruits, vegetables and other plant foods that have certain phytochemicals in them. Some of the ways in which this is brought about by the phytochemicals have been described above.
Some of the most beneficial phytochemicals are:
· The carotenoids in fruits and vegetables. Although beta carotene is the best known, there are well over 100, and possibly as many as 200, carotenoids in a carrot and it seems that it is the synergistic effect of all of these together that gives the best results. It is best to eat the whole fruit or vegetable rather than taking a supplement of a single one, for example, beta carotene.
· Resveratrol in wine. The resveratrol in wine, especially red wine, is health beneficial.
· Polyphenols in tea. Green and white teas have the highest amounts of polyphenols (see my September 2007 newsletter A Cup of Tea = A Cup of Good Health).
· Isothiocyanates in cruciferous vegetables. (See my October 2008 newsletter Cruciferous Vegetables.)
· Lycopene, as found in tomatoes. This is beneficial in heart disease and reduces the risk of prostate cancer. (See my December 2009 newsletter Lycopene - A powerful Antioxidant.)
· Lutein and Zeaxanthin. These may enhance visual performance and inhibit macular degeneration and cataracts.
Foods containing phytochemicals are already part of our normal diet. In fact, most foods contain phytochemicals, except for some refined foods such as sugar. The fruits and vegetables listed above have the highest amounts of health beneficial phytochemicals.
A plant-based diet, high in fruits and vegetables, with a low fat intake, is a healthy diet and should be an integral part of your lifestyle.
*Copyright 2010: The Huntly Centre.
Disclaimer: All material in the Huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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