Foods to prevent cancer
“What we’re seeing is many of them (supplements) are not appearing to be beneficial in the way that we had anticipated and could be harmful,” said Professor Jane Figueiredo, assistant professor of preventative medicine at the University of Southern California’s Keck School of Medicine in Los Angeles (Globe and Mail, 11.3.09).
“The prospects for cancer prevention through micronutrient supplementation have never looked worse,” said Alan Kristal of the Fred Hutchinson Cancer Research Center in Seattle and Scott Lippman of the department of thoracic/head and neck medical oncology at the University of Texas M.D. Anderson Cancer Center. (Source: Globe and Mail)
Where cancer is concerned, based on scientific evidence, the following supplements belong in the trash:
Folic acid supplements — may promote cancer. Several studies have associated folic acid, a B vitamin, with lower risk for some cancers. However, like several other vitamins, there is evidence that folic acid may be protective in moderate doses, but when consumed at very high amounts, may actually promote cancer. New research suggests that men who take folic acid supplements may be putting themselves at significantly greater risk for developing prostate cancer.
Beta carotene supplements – useless against cancer. Two independent studies showed that beta carotene supplements increased lung cancer risk in smokers. In December 2007 the American health advocacy group Center for Science in the Public Interest petitioned the Food and Drug Administration to require labels on beta-carotene supplements warning smokers about the risk. Beta carotene supplements also increased the risk of other cancers, heart attack, and stroke. But foods that contain beta carotene seem to reduce cancer risk.
Vitamins C and E supplements – won’t help prevent cancer. This was the finding of a large long-term clinical trial in the US.
What Experts Say
Eat Whole Foods. Not isolated compounds in supplements. And eat a variety of foods. Food is very complex. There isn’t a single element in a particular food that does all the work in fighting disease. Vitamins and nutrients in food interact with each other to produce benefits greater than any single one can deliver. Many health groups and experts recommend consuming antioxidants (eg: Vitamins C and E), through foods instead of supplements. (Antioxidants are substances that may protect the body’s cells against free radical damage, which contributes to heart disease, cancer and other diseases.)
They also recommend exercise and other lifestyle measures to beat cancer.
Here’s what they say:
- American Cancer Society nutritional epidemiologist Marjorie McCullough, ScD: “It is an old-fashioned message but it is important to eat a variety of foods, including plenty of fruits and vegetables. If people really would do this it would go a long way to ensuring that they get the nutrients and phytochemicals that may be important for reducing their cancer risk.”
- Jennifer Crum, a nutritionist at the New York University Cancer Institute: “When you take the nutrient out of its natural environment, it may not be protective … When people make small changes for their health — exercising for 20-30 minutes a day, eating better — we see lower rates of cancer recurrence.” (Useful Tip: Begin by making small changes, such as exercising a little bit longer or adding another vegetable a day to your diet.)
- Dr Howard Sesso, assistant professor of medicine in the division of preventive medicine at Brigham and Women’s Hospital in Boston, US: “There are things we know about cancer prevention: eat a well-balanced diet, maintain a healthy weight, don’t smoke, and exercise regularly.”
- The American Institute for Cancer Research (AICR) recommends seeking cancer protection from a diet high in a variety of plant foods instead of relying on dietary supplements.
At the AICR’s annual research conference on 6 November 2008, a panel of leading scientists discussed the state of the evidence on dietary supplements and their effects on cancer risk and concluded that getting nutrients from whole foods rather than dietary supplements is best.
Robert S. Chapkin, Ph.D., of Texas A&M University, who specialises in research on omega-3 fatty acids in fish, said nutrients in whole foods may work together with dietary fibre to “superactivate the system”, and increase cancer protection in the large intestine by triggering a response that attacks damaged cells.
A protective set of reactions occur in the body when phytochemicals from broccoli (isothiocyanates) and garlic (organosulfur compounds) are eaten. Shivendra V. Singh, Ph.D., of the University of Pittsburgh discussed evidence indicating that these substances are more than just antioxidants. Under certain conditions they exhibit pro-oxidant effects in ways that seem to specifically target tumour cells.
What to Eat
What can you eat to prevent cancer? The US non-profit Cancer Cure Foundation recommends the following foods, which have the ability to help stave off cancer and some can even help inhibit cancer cells.
- 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 strong source of beta-carotene. Scientists also believe that avocados may also be useful in treating viral hepatitis (a cause of liver cancer), as well as other sources of liver damage.
- Broccoli, cabbage and cauliflower have a chemical component called indole-3-carbinol that can combat breast cancer by converting a cancer-promoting estrogen into a more protective variety. Broccoli also has the phytochemical sulforaphane, a product of glucoraphanin — believed to aid in preventing some types of cancer, like colon and rectal cancer. Sulforaphane induces the production of certain enzymes that can deactivate free radicals and carcinogens. The enzymes have been shown to inhibit the growth of tumours in laboratory animals.
- Carrots contain a lot of beta carotene, which may help reduce a wide range of cancers including lung, mouth, throat, stomach, intestine, bladder, prostate and breast. Some research indicated beta carotene may actually cause cancer, but this has not proven that eating carrots, unless in very large quantities (2-3 kg a day), can cause cancer. In fact, a substance called falcarinol that is found in carrots has been found to reduce the risk of cancer, according to researchers at Danish Institute of Agricultural Sciences. In tests, isolated cancer cells grow more slowly when exposed to falcarinol.
- Chilli peppers contain a chemical, capsaicin, which may neutralise certain cancer-causing substances (nitrosamines) and may help prevent cancers such as stomach cancer. At a cellular level, capsaicin induces a state called apoptosis (programmed cell death) in the cancer cells. You could say that it causes the cancer cell to commit suicide.
- Cruciferous vegetables (eg: broccoli, cauliflower, kale, Brussels sprouts, and cabbage) contain two antioxidants, lutein and zeaxanthin that may help decrease prostate and other cancers.
- Flax contains lignans, which may have an antioxidant effect and block or suppress cancerous changes. Flax is also high in omega-3 fatty acids, which are thought to protect against colon cancer and heart disease.
- Garlic has immune-enhancing allium compounds (dialyl sulfides) that appear to increase the activity of immune cells that fight cancer and indirectly help break down cancer-causing substances. These substances also help block carcinogens from entering cells and slow tumour development. Diallyl sulfide, a component of garlic oil, has also been shown to render carcinogens in the liver inactive. Studies have linked garlic — as well as onions, leeks, and chives — to lower risk of stomach and colon cancer. Dr Lenore Arab, professor of epidemiology and nutrition at the UNC-CH (University of North Carolina at Chapel Hill) schools of public health and medicine and colleagues analysed a number of studies and reported their findings in the October 2000 issue of the American Journal of Clinical Nutrition. According to the report, people who consume raw or cooked garlic regularly face about half the risk of stomach cancer and two-thirds the risk of colorectal cancer as people who eat little or none. Their studies didn’t show garlic supplements had the same effect. It is believed garlic may help prevent stomach cancer because it has anti-bacterial effects against a bacterium, Helicobacter pylori, found in the stomach and known to promote cancer there.
- Grapefruits, like oranges and other citrus fruits, contain monoterpenes, believed to help prevent cancer by sweeping carcinogens out of the body. Some studies show that grapefruit may inhibit the proliferation of breast-cancer cells in vitro. They also contain Vitamin C, beta-carotene, and folic acid.
- Red grapes contain bioflavonoids, powerful antioxidants that work as cancer preventives. Grapes are also a rich source of resveratrol, which inhibits the enzymes that can stimulate cancer-cell growth and suppress immune response. They also contain ellagic acid, a compound that blocks enzymes that are necessary for cancer cells — this appears to help slow the growth of tumours.
- Studies show that consumption of green and yellow leafy vegetables has been associated with lower levels of stomach cancer.
- Kale has indoles, nitrogen compounds which may help stop the conversion of certain lesions to cancerous cells in estrogen-sensitive tissues. In addition, isothiocyanates, phytochemicals found in kale, are thought to suppress tumour growth and block cancer-causing substances from reaching their targets.
- Mushrooms — A number of mushrooms appear to help the body fight cancer and build the immune system — eg: Shiitake, maitake, reishi, Agaricus blazei Murill, and Coriolus Versicolor. These mushrooms contain polysaccharides, especially lentinan, powerful compounds that help in building immunity. They are a source of beta glucan. They also have a protein called lectin, which attacks cancerous cells and prevents them from multiplying. They also contain thioproline. These mushrooms can stimulate the production of interferon in the body. Extracts from mushrooms have been successfully tested in recent years in Japan as an adjunct to chemotherapy. The best-selling cancer medicine PSK (Protein-bound polysaccharide) is made from the Coriolus Versicolor. Maitake mushroom extract is PCM4 (an over-the-counter food supplement promoted for cancer in the US and Europe).
- Nuts contain the antioxidants quercetin and campferol that may suppress the growth of cancers. Nuts are one of nature’s best sources of selenium. (Brazil nut, for example, contains 80 micrograms of selenium, which is important for those with prostate cancer.) Selenium has been shown to improve the efficiency with which DNA repairs itself after exposure to damaging free radicals. Nuts also contain omega-3 fatty acid. The omega-3 fatty acids block a protein that has been shown to increase sensitivity to carcinogens in laboratory studies. (Note: Some people are allergic to the proteins in nuts, so if you have any symptoms such as itchy mouth, tight throat, wheezing, etc, after eating nuts, stop and seek help to eliminate this allergy.)
- Oranges and lemons contain limonene which stimulates cancer-killing immune cells (lymphocytes, for example) that may also break down cancer-causing substances.
- Papayas have Vitamin C that works as 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 to minimise cervical dysplasia and certain cancers.
- Raspberries contain many vitamins, minerals, plant compounds and antioxidants known as anthocyanins that may protect against cancer. According to a study reported by Cancer Research in 2001, rats fed diets of 5-10% black raspberries saw the number of esophageal tumours decrease by 43-62%. Research reported in the journal Nutrition and Cancer in May 2002 shows black raspberries may also thwart colon cancer. Black raspberries are rich in antioxidants, and are thought to have even more cancer-preventing properties than blueberries and strawberries.
- Seaweed & other sea vegetables contain beta-carotene, protein, Vitamin B12, fibre, and chlorophyll, as well as chlorophylones – important fatty acids that may help in the fight against breast cancer. Many sea vegetables also have high concentrations of the minerals potassium, calcium, magnesium, iron and iodine.
- Soy products like tofu contain several types of phytoestrogens — weak, nonsteroidal estrogens that 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 tumours require to flourish and is being scrutinised as a potential anti-cancer drug. However, there are some precautions to consider when adding soy to your diet. Eating up to 4-5 ounces of tofu or other soy a day is probably ok, but research is being done to see if loading up on soy could cause hormone imbalances that stimulate cancer growth.
- 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 antioxidants known as polyphenols (catechins) which appear to prevent cancer cells from dividing. Green tea is best, 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, these polyphenols that are abundant in green tea, red wine and olive oil, may protect against various types of cancer. 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, study findings have suggested. Green tea also contains the phytochemical epigallocatechin gallate (EGCG), which binds to a protein found on tumour cells and dramatically slows their growth.
- Tomatoes contain lycopene, an antioxidant that attacks roaming oxygen molecules, known as free radicals, that are suspected of triggering cancer. It appears that the hotter the weather, the more lycopene tomatoes produce. They also have Vitamin C, an antioxidant which can prevent cellular damage that leads to cancer. Watermelons, carrots, and red peppers also contain these substances, but in lesser quantities. It is concentrated by cooking tomatoes. 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. (Note: Recent studies indicate that for proper absorption, the body also needs some oil along with lycopene.)
- Tumeric (curcuma longa), a member of the ginger family, is believed to have medicinal properties because it inhibits production of the inflammation-related enzyme cyclo-oxygenase 2 (COX-2), levels of which are abnormally high in certain inflammatory diseases and cancers, especially bowel and colon cancer. In fact, a pharmaceutical company Phytopharm in the UK hopes to introduce a natural product, P54, that contains certain volatile oils, which greatly increase the potency of the tumeric spice.
According to a report in Medical News Today (29 March 2007), the following foods also show promise against cancer.
- High-fibre foods. A dietary component found in most whole grain foods, beans, nuts and other high-fibre items shows promise in animal studies as a potent weapon for preventing prostate cancer. The compound, inositol hexaphosphate (IP6), was fed to animal models of prostate cancer and resulted in up to a 66% reduction in tumour size in comparison to control animals that were given water instead, says Rajesh Agarwal, Ph.D., a professor in the Department of Pharmaceutical Sciences at the University of Colorado Health Sciences Center in Denver, in the US.
- Apple juice. Drinking cloudy apple juice (unfiltered apple juice, along with its fibre) daily may help prevent colon cancer. Researchers in Germany say that drinking 2-3 glasses of cloudy apple juice per day may help keep colon cancer at bay. In a 10-week study using a mouse model for colon cancer, animals that were fed either cloudy apple juice or a potent extract of the juice showed a 38% and 40% reduction (respectively) in benign tumours of the small intestine, an indicator of its potential to fight colon cancer, in comparison to control animals that were given water instead of juice, according to Clarissa Gerhäuser, Ph.D., a researcher with the German Cancer Research Center in Heidelberg. The anticancer effect is likely due to a potent class of antioxidants called procyanidins, the researcher says. A widely publicised recent study by a group of researchers in Poland found that cloudy apple juice also is richer in antioxidants — up to 4 times higher — than clear apple juice.
If you are a cancer patient, diet may still help. According to Science Daily (24 October 2008), preliminary findings from a 5-year US government-funded study by University of California-Riverside shows eating fruits and vegetables can improve cancer patients’ response to chemotherapy. In all cancer patients the leading cause of death continues to be the resistance of tumour cells to chemotherapy, a form of treatment in which chemicals are used to kill cells.
Ingesting apigenin can help, the study says. Apigenin is mainly found in fruits (including apples, cherries, grapes), vegetables (including parsley, artichoke, basil, celery), nuts and plant-derived beverages (including tea and wine). It has been shown by researchers to have growth inhibitory properties in several cancer lines, including breast, colon, skin, thyroid and leukaemia cells. It has also been shown to inhibit pancreatic cancer cell proliferation.
The study, published in the online early edition of the Proceedings of the National Academy of Sciences, suggests developing safe chemotherapy via naturally occurring agents such as apigenin.
Read about how protective foods like fruits and vegetables give us the antioxidants that we need to prevent cancer in the CAP Guides, Fruits – A Nutrition Guide and Vegetables – A Nutrition Guide