Plant-based foods with known anticarcinogenic properties are consumed to help prevent and treat cancer. Those that have been well researched are phytochemicals and antioxidants. Phytochemicals are chemicals that occur naturally in plants. Several hundred types of phytochemicals have been identified, but it is not yet known how many hundreds more phytochemicals may exist and precisely how they affect cancer cells. Examples of known phytochemicals include indoles in cabbage or cauliflower, saponins in peas and beans, sulforaphane in broccoli, genstain in soybeans, and isoflavones in soy milk and tofu. In the last several decades, nutrition scientists have consistently found that individuals who eat greater amounts of vegetables and fruits have lower rates of cancer. The mechanisms by which phytochemicals may assist the body in resisting cancer are just beginning to be understood. Laboratory studies suggest that the phytochemicals present in fruits and vegetables may offer protection by protecting cellular health and/or curbing the growth of malignant cells. It is not known whether the effects of phytochemicals may also modify the faulty protein expression by mutated genes, the process that causes the uncontrolled growth of cancer cells in the first place. Ongoing research is investigating the effects of phytochemicals more closely.
The antioxidants found in fruits, vegetables, and other plant-based foods fight free radicals, which are compounds in the body that attack and destroy cell membranes. The uncontrolled activity of free radicals is believed to cause many cancers. Examples of antioxidants include the carotenoids beta-carotene, lycopene, and vitamins A, C, and E; and flavanoids called anthocyanins.
The carotenoids, in particular, which give fruits and vegetables their bright yellow, orange, and red colors, are now gaining recognition for their nutritional value. Numerous studies have found that lycopene, the carotenoid that makes tomatoes red, helps to prevent prostate cancer. A study conducted at Harvard University found that men who consumed tomatoes or tomato-based products twice a week reduced risk of developing prostate cancer by one-third compared with men who did not consume tomatoes.
Other lycopene-rich foods, such as watermelon, red grapefruit, and guava, are now piquing the interest of researchers. Watermelon not only yields more lycopene per serving (15 mg in 1 1/2 cups) than raw tomatoes (11 mg per 1 1/2 cups), but is also a rich source of vitamins A and C.
Anthocyanins, also called anthocyanadins (anthocyanins with an extra glucose molecule) and anthocyans, are water-soluble pigments in a class of compounds known as flavonoids. They are found in water-filled compartments (vacuoles) in the cells of nearly all tissues of higher plants, including the roots, stems, leaves, flowers, and fruits. Some especially colorful, darkly pigmented plants (for example, raspberries, blueberries, cranberries, elderberries, acai, black cherries, pomegranate, blood oranges, purple corn, eggplant, red cabbage, and sweet peppers) contain high levels of anthocyanins. The leaves of colorful edible plants such as berries may even have tenfold the quantity of anthocyanins as the fruit itself. Research has confirmed that anthocyanins exert powerful antioxidant activity in vitro (in the laboratory, not in the body), but it remains unknown whether this activity may be diminished in the body after digestion. Nevertheless, the anthocyanins in colorful berries and other fruits and vegetables are reported to fight oxidative stress and the associated inflammation that may lead to Parkinson disease, Alzheimer disease, amyotrophic lateral sclerosis (ALS or Lou Gehrig disease), cancer, and various allergic disorders. They also exert antiviral, antibacterial, and antiparasitic activity although the mechanisms of action are not understood entirely. Whether antioxidants can reduce the incidence of cancer is still uncertain because of insufficient study data. Dietary sources are especially important because the benefits of supplements have not been demonstrated.
A number of foods are thought to have the ability to help prevent or treat cancer, and some are even thought to help inhibit cancer cell growth and reduce tumor size. Some of the foods and the nutrients they contain that have demonstrated an ability to support cancer prevention and/or treatment include:
AVOCADOS. Avocados are rich in glutathione, a powerful antioxidant that attacks free radicals in the body by blocking intestinal absorption of certain fats. They also supply even more potassium than bananas and are a good source of vitamin E. Scientists believe that avocados may be useful in treating viral hepatitis, especially hepatitis B (HBV) and hepatitis C (HCV), which often progress to cirrhosis of the liver and liver cancer (hepatocellular carcinoma).
BEANS. Beans contain a rich supply of phytochemicals that have been shown to prevent or slow genetic damage to cells. Study results suggest beans are especially effective in preventing prostate cancer. The high fiber content of beans has also been linked to lower risk of developing digestive system cancers such as stomach and colon cancer.
BERRIES. The two most widely studied cancer-fighting compounds in berries are ellagic acid (richest in strawberries and raspberries) and anthocyanins, which are richest in colorful blueberries, raspberries and strawberries. Ellagic acid is believed to help prevent skin, bladder, lung, and breast cancers, both by acting as an antioxidant and by slowing the reproduction of cancer cells. The anthocyanins in berries are reported to fight oxidative stress and associated inflammation that may lead to Parkinson disease, Alzheimer disease, amyotrophic lateral sclerosis (ALS or Lou Gehrig disease), cancer, and various allergic disorders. They also exert antiviral, antibacterial, and antiparasitic activity although the mechanisms of action are not understood entirely. The anthocyanosides in blueberries are currently the most powerful antioxidants known to scientists and are beneficial in the prevention of all types of cancer. Raspberries contain many vitamins, minerals, plant compounds, and antioxidant-rich anthocyanins that may protect against cancer. Research conducted in 2011 on the effects of strawberries supported the connection between berry intake and decreased risk of esophageal cancer.
CARROTS. Carrots contain large amounts of beta-carotene that may help reduce a wide range of cancers, including lung, mouth, throat, stomach, colon, bladder, prostate, and breast cancers. Conflicting study results have indicated that beta-carotene may actually cause cancer if consumed in very large quantities such as 4.4-6.6 lb. (2-3 kg). In fact, carrots contain a polyacetylene known as falcarinol that has been shown to reduce the risk of cancer. Isolated cancer cells have been shown to grow more slowly when exposed to falcarinol. Nevertheless, dietary sources of beta-carotene are the best because they carry no risk, whereas supplements can increase beta-carotene too much, and excess has been shown to have toxic effects in some individuals.
CHILI PEPPERS. Chili peppers and jalapenos contain a chemical, capsaicin, which may neutralize certain cancer-causing substances called nitrosamines and may help prevent cancers such as stomach cancer.
CITRUS FRUITS. Oranges and lemons both contain limonene, which stimulates cancer-killing immune cells such as lymphocytes that may also function in breaking down cancer-causing substances. Like oranges and other citrus fruits, grapefruit contains monoterpenes, which are believed to help prevent cancer by sweeping carcinogens out of the body. Studies have shown that grapefruit may inhibit the proliferation of breast-cancer cells in vitro. Grapefruits also contain vitamin C, beta-carotene, and folic acid.
CRUCIFEROUS VEGETABLES. All cruciferous vegetables, including cabbage, cauliflower, broccoli, and brussels sprouts, are members of the Brassicaceae, or Cruciferae family. They are rich in compounds that have been shown in studies to slow cancer growth and development. These vegetables contain a chemical component called indole-3-carbinol that combats breast cancer by converting a cancer-promoting estrogen into a more protective variety. Large human studies have shown that cruciferous vegetables help to reduce the risk of lung and bladder cancers. Also containing the antioxidants lutein and zeaxanthin, cruciferous vegetables may help decrease the risk of prostate and other cancers.
DARK GREEN LEAFY VEGETABLES. Green leafy vegetables, including kale, spinach, collards, chard, romaine lettuce, mustard greens, and chicory are rich sources of polyphenols called carotenoids. These antioxidant compounds scavenge dangerous free radicals from the body before they can promote the development of cancer. The vegetables are also rich in folate, a vitamin also shown in animal studies to reduce the risk of certain cancers.
FIGS. Figs contain a derivative of benzaldehyde as well as vitamins A and C, and minerals calcium, magnesium, and potassium. Investigators at the Institute of Physical and Chemical Research in Tokyo report that benzaldehyde is highly effective at shrinking tumors, although further experiments are required to confirm the initial findings. In addition, the U.S. Department of Agriculture says that figs may suppress appetite and improve weight-loss efforts. Fig juice is also a potent antibacterial in laboratory experiments, but this needs confirmation in clinical studies.
FLAXSEED. Flaxseed and flaxseed oil are shown to have potent anti-inflammatory and antioxidant effects due to high omega-3 fatty acid content. Flaxseeds are also the richest dietary source of lignan precursors, a group of phytonutrients or plant estrogens (phytoestrogens) that exhibit weak estrogenic activity and are thought to help reduce breast cancer risk. Although lignans are part of a healthy diet and appear to block or suppress cancerous changes, their role in the prevention of hormone-associated cancers such as breast cancer or endometrial cancer is not entirely clear. Although flaxseeds and flaxseed meal contain lignans and pure flax oil (which does not contain flaxseed protein or fiber) does not, some manufacturers have added lignans in commercial flax oil and will label it as such. Research results on the anticancer effects of flaxseed have contributed to a specialized diet designed by Dr. Johanna Budwig. Called the Budwig Diet (or Budwig Protocol), the dietary protocol uses the simultaneous consumption of flaxseed oil and cottage cheese to increase levels of phosphatides and lipoproteins in the blood. Dr. Budwig claims that the combination can both prevent and treat cancer, but supportive evidence is not sufficient.
GARLIC. Garlic has immune-enhancing allium compounds (diallyl sulfides) that appear to increase the activity of immune cells that inhibit the growth of cancer cells and indirectly help break down cancer causing substances. These substances also help block carcinogens from entering cells, thereby slowing tumor development. Diallyl sulfide, a component of garlic oil, has also been shown to render carcinogens in the liver inactive. Some studies have linked garlic, as well as onions, leeks, and chives to lower risk of a variety of cancers, including stomach, colon, lung, and skin cancer. Studies have shown that individuals who consume raw or cooked garlic regularly have about half the risk of stomach cancer and two-thirds the risk of colorectal cancer as individuals who eat little or none, although it is difficult for such studies to eliminate the effects of other dietary differences. The specific antibacterial effects of garlic against Helicobacter pylori, a bacterium found in the stomach and known to promote cancer, may be the source of the anticancer effects of garlic.
GRAPES AND RED WINE. Red and purple grapes are a rich source of resveratrol, a potent antioxidant and anti-inflammatory agent that inhibits cell proliferation and, as such, may help prevent cancer. Grapes also contain ellagic acid, a compound that blocks enzymes that are necessary for cancer cell growth, which helps to slow the growth of tumors and helps prevent the spread of cancer cells to other sites in the body. Red grapes also contain the polyphenols known as bioflavonoids, which are powerful plant-based antioxidants.
Red wine also contains the compound resveratrol because it is present in grape skins, and polyphenols, the potent antioxidants that neutralize disease-causing free radicals. The compound resveratrol is readily available in grape seed extract, which is the safest way to take it as protection against cancer. Increasing the amount of wine consumed is not the ideal way to obtain resveratrol as alcohol is increases risk of some cancers and can be toxic to the liver and nervous system. In addition, most wines have added sulfites that may be harmful to your health when consumed in large amounts.
LICORICE ROOT. Licorice root contains glycyrrhizin, a chemical that blocks a component of testosterone. Although licorice has been shown to help prevent the growth of prostate cancer, excessive amounts cause fluid retention in the body and also can lead to elevated blood pressure.
NUTS. Many nuts contain the antioxidants quercetin and campferol that may suppress the uncontrolled growth of tumor cells. Brazil nuts contain 80 micrograms of selenium, which is an antioxidant thought to be important in reducing risk of prostate cancer.
PAPAYAS. Papayas are rich in vitamin C, which is an antioxidant and may also reduce absorption of cancer-causing nitrosamines from the soil or processed foods. Papaya contains folacin (also known as folic acid), which has been shown in laboratory studies to reduce the risk of cervical dysplasia and development of certain cancers.
ROSEMARY. Rosemary may help increase the activity of detoxifying enzymes. An extract of rosemary, termed carnosol, has inhibited the development of both breast and skin tumors in animals. No comparable studies have been conducted on humans. Rosemary can be used as a seasoning and can also be consumed as a tea.
SEAWEED AND OTHER SEA VEGETABLES. Sea vegetables contain beta-carotene, protein, vitamin B12, fiber, and chlorophyll, as well as chlorophylones, which are important fatty acids that may help combat breast cancer. Most dried sea vegetables also have high concentrations of the minerals potassium, calcium, magnesium, iron, and iodine.
SOY PRODUCTS. Soy products like tofu contain several types of phytoestrogens which are weak, non-steroidal estrogens that resemble some of the body's natural hormones. These compounds could help prevent both breast and prostate cancer by blocking and suppressing cancerous changes. There are a number of isoflavones in soy products, but research has shown that genistein is the most potent inhibitor of the growth and spread of cancerous cells. It appears to lower breast cancer risk by inhibiting the growth of epithelial cells and new blood vessels that tumors require to flourish and is being scrutinized as a potential anticancer drug. Some precautions need to be considered when adding soy to the diet. Eating up to four or five ounces of tofu or other soy products a day is probably fine, but research is being done to see if high intake of soy could cause hormone imbalances that stimulate cancer growth. As a precaution, women who have breast cancer or are at high risk should talk to their doctors before taking pure isoflavone powder and pills, which are extracted from soy.
SWEET POTATOES. Sweet potatoes contain many anticancer properties, including beta-carotene, which may protect DNA in the cell nucleus from cancer-causing chemicals outside the nuclear membrane.
TEAS. Green tea and black tea contain certain anti-oxidants known as polyphenols (catechins) that appear to prevent cancer cells from dividing. Green tea is richest in these substances, followed by black tea (herbal teas do not show this benefit). According to a report in the July 2001 issue of the Journal of Cellular Biochemistry, the polyphenols that are abundant in green tea, red wine, and olive oil may protect against various types of cancer. Study findings have suggested that dry green tea leaves, which are about 40% polyphenols by weight, may also reduce the risk of cancer of the stomach, lung, colon, rectum, liver, and pancreas.
TOMATOES. Tomatoes contain lycopene, an antioxidant that attacks roaming oxygen molecules, known as free radicals, which are suspected of triggering cancer. Lycopene appears to be more easily absorbed if the tomatoes are eaten in processed form, either as tomato sauce, paste, or juice. It appears that the hotter the weather, the more lycopene tomatoes produce. Lycopene has been shown to be especially potent in combating prostate cancer and may also protect against breast, lung, stomach, and pancreatic cancer. Scientists in Israel have shown that lycopene can kill mouth cancer cells. An increased intake of lycopene has already been linked to a reduced risk of breast, prostate, pancreas, and colorectal cancer. Other studies indicate that for proper absorption, the body also needs some oil along with lycopene. Tomatoes also have vitamin C, an antioxidant that can prevent cellular damage that leads to cancer. Water-melons, carrots, and red peppers also contain these substances, but in lesser quantities. It is concentrated by cooking tomatoes.
WHOLE GRAINS. Whole grains contain a variety of anticancer compounds, including fiber, antioxidants, and phytoestrogens. When eaten as part of a balanced diet, high intake of whole grains is associated with reduced risk of developing most types of cancer.
In addition to the accumulated information about specific foods and food categories and the nutrients thought to support cancer prevention and treatment, the American Institute of Cancer Research (AICR) maintains a list of foods containing nutrients that have demonstrated an ability to prevent or treat cancer. The list is constantly updated based on high-quality research and provides references to recent studies. In 2017, the continuously updated list included:
The benefits of the recommended foods can, of course, also be obtained from supplements containing vitamins and minerals; however, vitamin and mineral supplements are not a total replacement for real food because these preparations do not supply the hundreds, even thousands, of phytochemicals and antioxidants that might be present in fruits and vegetables. For example, eating a sweet potato with its skin, which is a great source of both beta carotene and fiber, provides at least 5,000 phytochemicals that are not present in a beta-carotene supplement. Also, food sources of beta-carotene are well assimilated and carry no risk, but supplemental beta-carotene is not assimilated in the same way and can lead to accumulation and toxic effects. Isolating a few compounds in a tablet or liquid preparation will not provide the same protective benefits that plant foods provide; the body knows the difference between metabolizing synthetic vitamins and minerals vs. whole foods. Phytochemicals are best obtained by eating a good variety of plant foods every day. Whether fruits and vegetables are consumed in raw or cooked form does not really matter with regard to phytochemical content. While raw or steamed vegetables provide the best nutrient value, even canned and frozen fruits and vegetables still pack a phytochemical punch.
Although a considerable amount of information and knowledge has been accumulated regarding cancer-fighting foods, no single food or food substance can protect an individual against cancer, but the right combination of plant-based foods in the diet can greatly decrease the risk of developing cancer. Evidence is mounting that the minerals, vitamins, antioxidants, and phytochemicals in many plant foods interact to provide extra cancer protection by working synergistically. Most of the evidence has been obtained through laboratory studies and not in humans; more human studies are needed to confirm the effects of cancer-fighting foods in the body. Nevertheless, many nutrition scientists recommend that at least two-thirds of a dietary plan should consist of vegetables, fruits, whole grains, and beans to supply nutrients with cancer-fighting potential.
Research shows that children can benefit greatly from a diet rich in foods with nutrients that help prevent or treat cancer. A healthy diet promotes a lifetime of good health as well as supporting proper growth. Vitamin supplementation, however, is not recommended without obtaining the advice of a physician, nutritionist, or registered dietitian, because children have different vitamin requirements and adult dosages may not be appropriate.
See also Antioxidants ; Cancer ; Cancer diet ; Carotenoids ; Fats ; Minerals ; Omega-3 and omega-6 fatty acids ; Protein ; Vitamins ; Whole grains .
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Revised by L. Lee Culvert