Epidemiology: As a rule, the human immune system is able to stop carcinogens from damaging cells within the body. However, sometimes cell deoxyribonucleic acid (DNA) is attacked and altered, causing cancer cells to begin to develop and multiply. Studies show that most cancers can be prevented through lifestyle choices (a healthful diet, avoidance of tobacco and excessive alcohol use, and adequate physical activity) and changes in the environment. Strong associations link diet to some cancers, but many other factors contribute as well. Genetics, infectious agents, some viruses, and exposure to radiation, chemicals, and some carcinogenic substances in the air, water, and soil also play a role. In 2014, the CDC reported that 22.9 percent of deaths in the United States in 2009 were due to cancer.
Nutrition risk factors: Studies find populations that eat a diet rich in fatty foods, especially animal fats, have higher rates of cancer than populations that eat a plant-based diet high in whole grains, vegetables, fruits, and legumes. Increased death rates from breast, prostate, and colon cancers are associated with high-fat diets. Higher rates of cancer have also been linked with the consumption of low-fiber diets and excessive alcohol.
Being overweight or obese is also strongly linked with cancer. Overweight people are more likely to develop breast (postmenopausal women), colon, endometrial, esophageal, pancreatic, and kidney cancers. Obese individuals are also at risk for developing cervical, gallbladder, ovarian, liver, and colorectal cancers; non-Hodgkin lymphoma; multiple myeloma; and aggressive forms of prostate cancer. These findings are of particular concern as westernized societies are experiencing increasing rates of obesity.
Excessive alcohol intake, defined as more than two drinks per day for men and more than one drink per day for women (one serving equals 5 ounces of wine, 12 ounces of beer, or 1.5 ounces of liquor), is clearly associated with cancers of the mouth, throat, larynx, esophagus, liver, and breast.
No known nutrition factors are associated with brain cancer, leukemia, and lymphoma. However, some cancers related to diet may result in secondary tumors or metastatic disease in these areas.
Research findings: A number of different food compounds, minerals, and vitamins are thought to protect against some cancers. Some of those that have become well known are antioxidants, carotenoids, and phytochemicals, substances or nutrients found in foods. Antioxidants include vitamins C and E and the mineral selenium; carotenoids include lycopene, lutein, and beta-carotene; and phytochemicals include a number of plant-based compounds, such as resveratrol (found in red wine), catechin (found in teas), and allium (found in garlic). The use of dietary supplements containing these substances has increased dramatically in the United States because of the popular belief that they prevent aging and illness.
Research shows that antioxidants, carotenoids, and phytochemicals do have some protective effects against free radicals, which are cell-damaging molecules arising from normal biological functions and the environment. Free radical cell destruction is believed to cause aging and many diseases in humans. However, although some studies show benefits from including antioxidants, carotenoids, and phytochemicals in the diet, other studies actually show that they can cause harm. In two studies in which high doses of beta-carotene supplements were taken to prevent lung cancer, former cigarette smokers experienced increased lung cancer death. However, when beta-carotene was consumed via food sources (not supplements), cancer risk was reduced.
In the past, coffee, aspartame, saccharin, and sugar were suspected of causing cancer, but studies did not conclusively link them to cancer in humans. An increased cancer risk has been associated, however, with the consumption of highly salted, preserved, or smoked meats and those cooked at high temperatures (fried, broiled, and grilled). Many experts recommend limiting consumption of these types of meats and using lower-temperature cooking methods, such as poaching.
Studies regarding concerns over the effects of bioengineered and irradiated foods, fish contaminated with mercury, food additives, fluoride in dental products and water, and pesticide residue on foods have not shown increased risk for cancer. There is no evidence to date that distinguishes organic foods from conventional foods in terms of a cancer risk. However, some studies have shown that the phytochemical content of organic fruits and vegetables may be higher than that of conventionally grown crops. This finding leads some to think that this might convey some level of protection against cancer.
Soy, calcium, and vitamin D are thought by some to help prevent cancers. Soy is an excellent source of protein and phytochemicals, but findings regarding the premise that soy lowers the risk of cancer have been mixed. Soy contains compounds called phytoestrogens (plant estrogens), which closely resemble the hormone estrogen and may actually increase the risk of estrogen-responsive cancers, such as breast and endometrial cancers. It may also reduce the effectiveness of tamoxifen drug treatments. Therefore, some researchers recommend that soy foods and products containing soy isoflavones should be limited to three servings per day and that dietary soy supplements should be avoided. Patients taking tamoxifen should consult their physician before consuming any soy products. The connection between soy and cancer, however, remains unclear.
Calcium has been associated with a lower incidence of colorectal cancers, but there is also evidence that calcium supplements may increase prostate cancers, especially the aggressive form. Because of this, calcium recommendations remain at 1,000 milligrams per day for people between the ages of nineteen and fifty and 1,200 milligrams per day for people older than fifty. Nonfat or low-fat dairy sources of calcium and some leafy green vegetables are preferable to supplements as sources of calcium. Vitamin D is also increasingly thought to protect against colorectal, prostate, pancreatic, and breast cancer. The Institute of Medicine (IOM) recommendations for intake of vitamin D, as of 2010, are between 400 and 600 International Units (IU) daily for most people and 800 IU for those aged seventy and older; this may not be sufficient to provide protection against cancers, especially for those living in northern climates, people with dark skin, and exclusively breastfed babies. In the meantime, many researchers suggest balancing the diet to include foods fortified with vitamin D. Skin exposure to sunlight is one means by which the body can obtain vitamin D; however, the IOM is reluctant to recommend it due to the risk of skin cancer from ultraviolet (UV) radiation.
Many more studies need to be done to verify diet and cancer connections, but the best way for people to lower their cancer risk appears to be eating a balanced, low-fat diet that includes a variety of fruits and vegetables daily.
Dietary recommendations: Research points to a number of dietary recommendations that should be followed to lower the risk for developing cancer or having it recur. The following recommendations are from the American Cancer Society:
- Maintain a healthy weight throughout life: People are advised to lose weight if they are overweight or obese, avoid excessive weight gain, and balance food intake with physical activity.
- Adopt a physically active lifestyle: Adults are advised to exercise moderately at least 150 minutes a week or vigorously 75 minutes a week. Children and adolescents are advised to exercise at least 60 minutes per day, vigorously three or more days per week.
- Eat a healthy diet, with an emphasis on plant sources: People are advised to eat two-and-a-half cups or more of vegetables and fruits every day, choose whole grains, and include legumes for protein. Also, they are to limit intake of processed and refined foods, sugars, red meat, and processed meats. A simple way to make sure the diet has the right emphasis is to fill one-fourth of the plate with a protein source, one-fourth with whole grains, and one-half with colorful vegetables. One serving of fruit is one-half cup of canned fruit, three-quarters cup of 100 percent juice, or a small- to medium-sized piece of fresh fruit. One serving of vegetables is one-half cup of cooked or one cup of raw vegetables.
- Limit consumption of alcoholic beverages: Women should not exceed one drink per day, and men, two drinks per day.
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American Institute for Cancer Research. Diet and Health Recommendations for Cancer Prevention: Healthy Living and Lower Cancer Risk. Washington: Amer. Inst. for Cancer Research, 2006. Print.
Awad, Atif B., and Peter G. Bradford, eds. Nutrition and Cancer Prevention. Boca Raton: CRC, 2006. Print.
Doyle, Colleen. "From the Pyramid to the Plate." Cancer.org. Amer. Cancer Soc., 2 June 2011. Web. 30 Oct. 2014.
Kushi, Lawrence H., et al. “American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention.” Cancer: A Cancer Journal for Clinicians 56 (2006): 254–81. Print.
McTiernan, Anne, ed. Cancer Prevention and Management through Exercise and Weight Control. Boca Raton: Taylor, 2006. Print.
"Up to 40 Percent of Annual Deaths from Each of Five Leading US Causes Are Preventable." CDC. Centers for Disease Control and Prevention, 1 May 2014. Web. 30 Oct. 2014.
"Vitamin D and Cancer Prevention." Cancer.gov. Natl. Cancer Inst., Natl. Inst. of Health, 21 Oct. 2013. Web. 30 Oct. 2014.
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