Nutrition and cancer prevention
Nutrition plays a significant role in cancer prevention, as studies increasingly highlight the relationship between dietary habits, lifestyle choices, and cancer risk. According to research, approximately 45% of cancer deaths may be linked to modifiable risk factors, including diet and physical activity. Diets high in animal fats and low in fiber are associated with increased cancer rates, while plant-based diets rich in whole grains, fruits, and vegetables may reduce risk. Furthermore, being overweight or obese is strongly correlated with several types of cancer, including breast and prostate cancer.
Preventative measures include maintaining a healthy weight, engaging in regular physical activity, and adopting a balanced diet that emphasizes plant sources. The American Cancer Society recommends consuming a variety of vegetables and fruits daily, limiting processed foods and red meat, and moderating alcohol intake. Additionally, the consumption of certain nutrients and compounds, such as antioxidants and phytochemicals found in foods, may offer some protective benefits against cancer. However, the effectiveness of dietary supplements remains unclear, with some studies suggesting potential harm. Overall, fostering a healthful lifestyle is essential for lowering cancer risk.
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Nutrition and cancer prevention
DEFINITION: Everyday eating habits are increasingly associated with cancer incidence, prevention, and management. According to the American Cancer Society, in 2023, 45 percent of all cancer deaths could be attributable to risk factors that are potentially modifiable. They also estimated that the types of foods people eat and their levels of physical activity directly cause about 16 percent of cancer deaths. Studies show that diet and lifestyle changes can prevent and reduce the risk and recurrence of most cancers.
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, such as a healthful diet, avoidance of tobacco and excessive alcohol use, 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 2021, the Center for Disease Control (CDC) reported that 18 percent of deaths in the United States 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. According to the International Agency for Research on Cancer, overweight and obesity are associated with thirteen cancers in particular: breast (postmenopausal), colorectal, esophageal (adenocarcinoma), gallbladder, liver, kidney, meningioma, multiple myeloma (a blood cancer), ovarian, pancreatic, stomach, thyroid, and uterine. These findings are of particular concern as Westernized societies have experienced increased 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.
Preliminary research showed 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. The National Cancer Institute reported in 2017 that nine randomized controlled trials had found collectively found no benefit to consuming dietary antioxidant supplements for cancer prevention and that some other trials with cancer patients found that such supplements had worsened outcomes.
The epidemiological evidence for tea consumption and a lower risk of cancer has also been inconsistent. Tea may help reduce the drinker's risk of developing colon, breast, ovary, prostate, and lung cancers, but there are many possible confounding variables. Furthermore, several clinical trials conducted with at-risk precancerous populations reported no clear cancer prevention benefit.
In the past, coffee, aspartame, saccharin, and sugar were suspected of causing cancer, but studies did not conclusively link them to cancer in humans. Research has found, however, that consuming excess sugar or sweeteners contributes to diabetes and obesity, which are both proven risk factors for various cancers. The American Heart Association recommends that women consume no more than twenty-five grams of sugar a day and men consume no more than thirty-seven grams a day.
An increased cancer risk has been associated, however, with the consumption of highly salted, preserved, or smoked meats and those cooked for long periods or 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, set in 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: People should not consume more than two drinks per day, though any alcohol consumption can pose a risk of cancer. The recommendation is to cease alcohol intake altogether.
- Limit smoking and exposure to other carcinogens: Smoking has known links to cancer, particularly lung cancer, so it is advised not to smoke at all. It is also advised to avoid other carcinogens or, if you are exposed in the workplace, to protect yourself and receive annual health screenings.
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