Nutrition Connection: Nutrition, Cancer, and You
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(reprinted from Nutrition & Foodservice Edge, June 2012)
Nearly 19 million Americans or about 9 percent of the U.S.
population have been diagnosed with cancer. The term cancer
refers to more than 100 different types of cancers.
Cancer is characterized by an abnormal growth of cells, and is the
second leading cause of death in the U.S. Some of the most common
types include breast cancer, skin cancer, lung cancer, colon
cancer, prostate cancer, and lymphoma. Within each of these
types are many subcategories. Symptoms vary widely based on the
type of cancer. Cancer treatment is customized to each patient
based on the type of cell abnormality and the patient’s response
to treatment. It may include chemotherapy, radiation, surgery, or
a combination of interventions. The cost of cancer treatment is
staggering and expected to increase.
CANCER RISK FACTORS
Many people view their risk of getting cancer as higher or lower
than it actually is. The risk of developing cancer is based on
statistics associated with different types of cancers. While you
can never really know exactly your individual or personal cancer
risk, certain personal characteristics and behaviors increase
your chances of getting cancer. Research shows that behavioral,
biological, environmental, and genetic risk factors increase the
chance that a person will develop cancer. Risk factors are noted
in Table 1.
There is no substitute for good nutrition to reduce your risk for cancer, but good nutrition cannot guarantee you will never develop cancer. Using foods or dietary supplements to reduce the risk of developing cancer is called chemoprevention. There are many claims on the Internet and in print media citing specific foods or supplements will reduce your risk for cancer. Many of the claims are not based on science. However, some research studies demonstrate the relationship between food components and health. Many of these studies were done using animal models and the results may not apply to humans. The links between dietary intake and cancer are not fully understood.
Phytonutrients or phytochemicals refer to a wide variety of compounds produced by plants. These compounds are often referred to as the vitamins and minerals of the 21st century.
Table 1: Risk Factors for Cancer
|Behaviors you can change||Physical characteristics
you cannot change
|Things found in the
|Genes inherited from your
|Smoking/tobacco use||Gender||Sun/UV radiation||Family members diagnosed with cancer at a younger age than usual for that cancer|
|Alcohol consumptions and othe bioactive substances||Race||Scondhand smoke||3+ generations diagnosed with similar cancers|
|Diet||Age||Hazards at work or home: Radon, asbestos, pesticides, pollution||3+ generations on the same side of the family|
|Maintaining BMI within normal weight range or weight loss in individuals with BMI>25||Family members diagnosed with 2+ different kinds of cancer|
There are several major groups of phytochemicals including antioxidants, flavonoids, flavones, isoflavones, catechins, anthocyanidins, isothiocyanates, carotenoids, allyl sulfides, and polyphenols. Phytochemicals are promoted for the prevention and treatment of many health conditions, including cancer, heart disease, diabetes, and high blood pressure.
Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Free radical damage may lead to cancer. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals might otherwise cause. Examples of antioxidants include beta-carotene, lycopene and ascorbic acid, vitamin E, and vitamin A.
The majority of studies indicate a possible protective effect from soy foods against various cancers. Soy products contain five classes of anti-cancer agents including isoflavones, phytosterols, phytates, saponins, and protease inhibitors. Most of the research focuses on the isoflavones genistein and daidzein. These compounds appear to provide a mild estrogenic effect, which may reduce the risk of cancer by competing for estrogen receptors. Individuals who have a history of an estrogen-receptor positive disease may want to limit their intake of dietary soy and soy supplements until more research is published on the potential recurrence risk of an estrogen-dependent cancer.
Broccoli, cabbage, cauliflower, and Brussels sprouts are cruciferous vegetables containing sulforaphane and brassinin. These components have been shown to boost the body’s ability to defuse potential carcinogens. Indoles (in broccoli) may reduce the production of estrogen or change existing estrogen to the less harmful version.
Legumes contain various phytochemicals such as lignans, triterpenoids, flavonoids, inositol, protease inhibitors, sterols, and saponins which may help prevent cancer. The resistant starch in beans and peas (starch not digested in the small intestine) is used by healthful bacteria in the colon to produce short-chain fatty acids which seem to protect colon cells from DNA damage.
Spinach and other leafy greens
Dark green leafy vegetables contain glutathione, lutein, and zeaxanthin, which may reduce risk of lung cancer and promote strong immune function. Kale, collard greens, and spinach contain the highest levels of these carotenoids, ranging from 6,000-10,000 micrograms in a serving.
Grapes contain resveratrol, an antioxidant, which has been shown to reduce tumor incidence in animals by affecting one or more stages of cancer development. The skin of the grape contains the most resveratrol, and red and purple grapes contain significantly more resveratrol than green grapes. Grape jam and raisins contain much smaller amounts of this phytochemical. Grapes also contain powerful flavonoids, quercetin, anthocyanin, and catechin, which are antioxidants.
When wine is made from these grapes, the alcohol produced by the fermentation process dissolves the polyphenols contained in the skin and seeds. Red wine contains more polyphenols than white wine because the making of white wine requires the removal of the skins after the grapes are crushed. Research studies examining the association between red wine consumption and cancer in humans are in their initial stages. Although consumption of large amounts of alcoholic beverages may increase the risk of some cancers, there is growing evidence that the health benefits of red wine are related to its nonalcoholic components.
Berries and Walnuts
Raspberries, blackberries, cranberries, strawberries, pomegranates, pecans, and walnuts contain ellagic acid. Research in cell cultures and laboratory animals has found that ellagic acid may slow the growth of some tumors caused by certain carcinogens. However, there is no reliable evidence available from human clinical studies showing that ellagic acid can prevent or treat cancer.
Tomatoes are rich in a carotenoid called lycopene. Lycopene is a carotenoid present in human serum and skin as well as the liver, adrenal glands, lungs, prostate, and colon. Lycopene has been found to possess antioxidant and antiproliferative properties in animal and laboratory studies, although activity in humans remains controversial.
Numerous studies correlate high intake of lycopene-containing foods or high lycopene serum levels with reduced incidence of cancer, cardiovascular disease, and macular degeneration. However, estimates of lycopene consumption have been based on reported tomato intake, not on the use of lycopene supplements. Since tomatoes are sources of other nutrients, including vitamin C, folate, and potassium, it is not clear that lycopene itself is beneficial. There is no well-established definition of “lycopene deficiency,” and direct evidence that repletion of low lycopene levels has any benefit is lacking.
Green and black tea contain polyphenols, catechins, and flavonoids. These components of tea appear to reduce the risk of cancer. Although many of the potential beneficial effects of tea have been attributed to the strong antioxidant activity of tea polyphenols, the precise mechanism by which tea might help prevent cancer has not been established. Moderate intake is best to avoid excess tannin consumption. Tea can reduce iron absorption when consumed with food. Key Nutrients , Dietary Supplements , and Cancer Ris k Generally speaking, foods containing dietary fiber lower the risk for colorectum cancers. Non-starchy vegetables and foods rich in carotenoids may lower the risk of cancers of the mouth, pharynx, larynx, and lung. Foods containing beta-carotene and those containing ascorbic acid may lower the risk for cancer of the esophagus.
Many claims are made on the Internet and in print media that taking dietary or herbal supplements will reduce the risk of cancer. Evidence from animal, in vitro and observational studies has suggested taking dietary supplements may lower cancer risk. However, the small number of randomized controlled studies has not confirmed this finding, and some studies actually have shown that supplements may increase cancer risk.
In preclinical trials, supplemental dietary antioxidants including beta-carotene, alpha-tocopherol, and ascorbic acid, encouraged growth of normal cells and tissue and inhibited growth of abnormal tissue. The effect of antioxidants was studied for several types of cancers. Unfortunately, clinical studies failed to support the favorable laboratory evidence.
• Beta-carotene did not prevent recurrence of non-melanoma skin cancer. • Beta-carotene, alpha-tocopherol, and ascorbic acid failed to prevent recurrence of colonic adenomas.
• Beta-carotene, vitamin A, and alpha-tocopherol did not prevent lung cancer. • Ascorbic acid and vitamin E did not protect against cancer.
• Alpha-tocopherol, ascorbic acid, and beta-carotene had no effect on cancer incidence or mortality.
• Beta-carotene, ascorbic acid, and vitamins A and E, either alone or in combination, did not prevent gastrointestinal cancers.
• Alpha-tocopherol and selenium failed to prevent prostate cancer in average-risk men.
Several antioxidant trials have shown increased cancer risk with supplementation. Two randomized trials of patients at high risk for lung cancer because of smoking or exposure to asbestos showed an increased incidence of lung cancer in participants randomized to beta-carotene.
Laboratory and observational data had suggested a protective effect of folic acid against cancer, particularly colorectal cancer. However, a meta-analysis of randomized trials showed no effect of folic acid supplementation on development of colorectal adenomas. Two different randomized trials showed an increased risk of prostate cancer and precancerous lesions (colonic adenomas) in participants on long-term folic acid supplementation.
The role of vitamin D in cancer prevention has been studied extensively. The Institute of Medicine report on vitamin D and calcium intake noted that “there was not enough evidence to state that there is a causal association between low vitamin D intake and increased cancer risk.” The mechanisms by which vitamin D may modify cancer risk are not fully understood. Laboratory studies have shown that vitamin D promotes cellular differentiation, decreases cancer cell growth, and stimulates death of abnormal cells.
Points to Ponder
Despite the volumes of research papers written about the nutrition- cancer connection, scientists have yet to unlock the etiology of most forms of cancer. Even the studies that show some relationship between food components and risk reduction draw few conclusions. Dietary supplements have not reduced risk for many types of cancer, and may in fact increase risk. Scientists agree that it is important to eat a variety of plant foods to ensure the most protection against cancer development. No food or dietary supplement in isolation can effectively lower cancer risk. More research is needed to clarify the true nutrition-cancer connection.
by Mary Litchford, PhD, RD, LDN
Mary Litchford, PhD, RD, LDN is a nationally-recognized speaker and the author of various articles and books, including Common Denominators of Declining Nutritional Status.