Nutrition, Genes, and Cancer Prevention

Q: How long have scientists known about the link between nutrition and ovarian, breast, and prostate cancers?

A: For many decades, the role of diet began to receive attention in the early 20th century, when food-coloring dyes were found to be carcinogenic. Studies of foods and food groups, individual nutrients, and dietary patterns followed, with an emphasis on seeking the cause of illness. For example, the first clues that foods might affect the course of breast cancer came from studies of women in Japan in the early 1960's. Compared with Western women, Japanese women were less likely to develop the disease and were more likely to survive if it occurred.

Back in the 1960's, we became aware that the environment might be playing a causative role in certain cancers. The government, in the early 1970's with the "war on cancer," led up to research requests in the late 1970's that resulted in efforts by researchers Doll and Peto to estimate how many cancer deaths resulted from diet and environment. Their landmark analysis, completed in 1981, set the stage for helping scientists and the public health community understand that a large percentage of cancer deaths were due to the environment and diet. No matter how much information we are able to report scientifically, in terms of "causes," there is also the aspect of "what are people going to do with it?" We know that eating too much can lead to obesity. It is not going to happen in a day; the same applies to other chronic diseases, of which cancer is one.
Q: How is nutrition involved in reproductive cancers?

A: In their 1981 analysis of the causes of cancer, Doll and Peto estimated that 35 percent of cancer deaths in the United States were attributable to dietary factors. The latest American Cancer Society estimates attribute about 33 percent of all cancer deaths to poor nutrition, physical inactivity, overweight, and obesity. We are at a stage of science where we have identified foods that suggest an increase risk for cancers and foods that help offer protection. Recent studies implicate components in dairy products might be linked to an increased risk for ovarian, breast, and prostate cancers. For ovarian cancer, galactose, a component of the milk sugar lactose, is under study as a possible culprit. In prostate cancer, both fat and a high calcium content may play a role. Dairy intake may increase levels of insulin-like growth factor I (IGF-I) in the body, a potent stimulus for cancer cell growth. High IGF-I levels are associated with an increased risk of prostate cancer and breast cancer.
Q: Which causes of cancer are considered to be under our control?

A. We know that total caloric and excess energy intake is related to cancer. The level of adiposity (body fat) is a factor as well. Components of a plant-based diet appear to protect against some cancers, whereas some animal products may increase risk.
Q: How do animal products contribute to the risk of reproductive cancers?

A: Some studies support an association between dietary fat (particularly saturated or animal fat) and prostate cancer. This may be a result of the meat as a source of omega-6 fatty acids, which offset the protective effects of omega-3 fatty acids. The way meat is cooked may also have an influence; grilling or frying produces harmful chemicals that are carcinogenic. Conversely, cooking a soy burger or a slice of tofu produces almost none of these chemicals. High intake of dairy foods is correlated with increased risk for prostate cancer and, in some studies, ovarian cancer. A high fat intake may raise the risk of breast cancer in postmenopausal women.
Q: How might a vegan diet (without any animal products) protect against cancer?

A: A balanced vegan diet can strengthen immunity, reduce oxidative stress, regulate blood sugar, and keep body weight stable. This diet can be a powerhouse of nutrients that may protect against cancer.
Q: Which components of foods might benefit cancer patients?

A: Results of one study in postmenopausal women with breast cancer found that reduced dietary fat and increased fiber, vegetable, fruit, and other nutrients associated with a plant-based, high-fiber diet improved overall survival after a diagnosis. In another study, soy offered protection for men with prostate cancer. Some studies show benefits of vitamin E, selenium, and lycopene for prostate cancer. Non-starchy vegetables may decrease the risk for ovarian cancer.
Q: Which mechanisms are associated with an optimal diet for cancer patients?

A: The immune system is critically important in fighting cancer. Individual cancer cells can arise in all of us from time to time. Cancer cells can also break free from an existing tumor and spread to other parts of the body. If the immune system is vigilant, it recognizes and destroys cancer cells-before they can take hold. So strengthening the immune system is a key strategy in cancer prevention and survival. Immune boosters include maintaining normal body weight and consuming beta-carotene, zinc, and vitamins C and E. Immune function inhibitors include fatty foods and cholesterol.
Q: Does obesity place individuals at higher risk for cancer?

A: Yes, overweight is a known risk factor as are body mass index (BMI) and intra-abdominal fat.
Q: Does smoking lessen the protective functions of healthful foods?

A: People who smoke tobacco have lower levels of important cancer-fighting antioxidants, including alpha- and beta-carotene, and vitamin C.
Q: Are there any subgroups of patients who should not follow nutritional advice?

A: People who are overweight, who have any health problem, or who are taking medications should consult with their doctors before making changes in diet or exercise.
Q: Do any essential nutrients place people at greater risk of cancer?

A: Large studies in England and Germany showed that vegetarians were about 40 percent less likely to develop cancer than meat eaters. In the United Kingdom Women's Cohort Study, women with the greatest intake of total meat, particularly processed meats, had the highest breast cancer rates. One reason might be the fat content of meat products, which are typically much higher than in plant foods. And because meat is not a plant product, it has no fiber. Meat is also devoid of vitamin C, and it is low in other protective nutrients found in plants.
Q: Which antioxidants are important for health?

A: Beta-carotene, vitamins C and E, lycopene, and anthocyanins are powerful antioxidants. Anthocyanins provide the color for cherries, plums, red cabbage, and blueberries. These antioxidant cancer fighters are found mainly in vegetables and fruits.
Q: What are the dangers of mega-doses of "anticancer agents?"

A: In general, there is no need to take megavitamin supplements. In the famous Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study, high supplement use of beta carotene increased the risk of cancer in current smokers. Some nutrients become impaired when people take mega-doses of others. Plant foods contain many anticancer nutrients in the proper amounts.
Q: Do any vitamin supplements come close to "the real thing?"

A: Probably selenium and lycopene come to mind.
Q: Which vitamins and nutrients might help decrease the likelihood of cancer recurrence?

A: Focusing on dietary patterns may offer a better approach in. cancer survivors. Breast cancer patients had better survival with foods low in fat (particularly saturated fat); with an increased intake of both fruits and vegetables; and with foods high in fiber. A plant-based diet, along with regular exercise and relaxation techniques, was found to slow prostate cancer progression, and the men were less likely to need additional treatment. Increased survival was also seen in prostate cancer patients who ate a macrobiotic diet emphasizing whole grains, vegetables, and legumes while avoiding dairy products and meats. Higher intake of non-starchy vegetables and isoflavone-rich soy foods has shown a protective effect against ovarian cancer.
Q: Why do certain combinations of foods work best when eaten together?

A: Foods can act synergistically with one another. For example, some vitamins and minerals are better absorbed when they are consumed with other foods. Foods that contain vitamin C help absorb iron, but consuming dairy products decreases the absorption of iron-containing foods.
Q: What role do hormones play in cancer risk?

A: Endogenous hormones, including both androgens and estrogens, may influence prostate cancer. In women, many breast cancers are hormone-dependent; that is, estrogen and progesterone stimulate cancer growth by "turning on" hormone receptors in the cancer, cells. The increase in breast cancer is not just a result of estrogen; studies of combined hormone replacement therapy with estrogen and progesterone also report an increased risk.
Q: Which genes might be responsible for the reproductive cancers?

A: Approximately 13 percent of all breast cancer cases are hereditary. Women with BRCA1 and BRCA2 gene mutations have a 60 to 80 percent lifetime risk for breast cancer and a 16 to 60 percent greater risk for ovarian cancer. About 5 percent of all breast cancers involve these gene mutations. Family history is one of the greatest risk factors for ovarian cancer. A particular region on chromosome 8q24 appears to be associated with an increased prostate cancer rate in African-American men.
Q: Are there any protective genes that might decrease the risk of reproductive cancers?

A: In one study, women with a version of the androgen receptor gene containing a short polyglutamine repeat tract (short- allele genotype) were 50 percent less likely to develop breast cancer, compared with women with a long-allele genotype. Approximately 16 percent of women have the short-allele genotype.
Q: Can lifestyle decrease the effects of cancer genes?

A: It is not entirely known, but women who carry the BRCA gene mutation should consider the same recommendations as those for non-carriers. These include a better diet, limiting alcohol, exercise, and maintaining a healthy weight. Some research suggests a favorable effect with the use of omega-3 fatty acids (from soy, walnuts, flax), plant-based compounds, soy compounds, and weight control. Others suggest that intake of selenium, lycopene, green tea, and cruciferous vegetables (broccoli, cabbage, cauliflower) may reduce risk of breast cancer in BRCA mutation carriers by reducing DNA damage. Vitamin D, by interacting with vitamin D receptors in the breast and other tissues, may be protective. The vitamin D receptor plays a role in how the body uses vitamin D. It occurs in at least two different genetic types. Individuals who inherit the "weak" type of receptor gene from both parents may be at an increased risk for breast cancer.
Q: Is the prostate-specific antigen (PSA) test accurate?

A: The advent of PSA screening for prostate cancer has resulted in more diagnoses of earlier-stage prostate cancer. However, many of these cancer cases are insignificant or of a low grade and may exist until the end of a person's life without causing harm. Therefore, the use of the test is controversial; some experts say that up to 50 percent of PSA-detected prostate cancers are considered insignificant.
Q: A 2007 cardiology study reported that very low cholesterol levels increased cancer risk, How would you interpret this?

A: The finding showed an association between cancer risk and reduced levels of low-density lipoprotein-cholesterol after therapy with statin drugs. There might be some connection with how statins affect the liver. It might also be that the presence of cancer itself disrupts cholesterol metabolism and causes cholesterol levels to drop, in which case the low cholesterol levels did not cause the cancer but, instead, were the result of the cancer.
Q: Are health professionals trained to look at diseases holistically?

A: Cancer patients tend to have a much better survival rate if they eat right. That shows how hard the body wants to correct itself. Even if cancer is diagnosed, it still can partially reverse itself or at least extend longevity if patients can follow some healthy practices. Most cancer patients do not make major life changes and do not follow these guidelines after their treatment.

Some say we need a different model than the current allopathic model of medicine, which treats disease instead of trying to prevent disease; this would take a lot more effort than a quick "one-pill" Solution. Unfortunately, many physicians and oncologists do not discuss the role of nutrition and diet, which is usually relegated to nutritionists and dietitians who have a limited amount of time to discuss these topics in depth with patients. Of course, "Rome was not built in a day," but it was not torn down in a day either. Changing long-term patterns does not happen in two one-hour consultation visits.
Q: Are some causes of cancer considered to be under our control?

A: Certainly, some things are beyond our ability to change, but many lifestyle changes might influence whether we increase or reduce our risk for certain cancers. The data show that we can decide many things, such as adding or eliminating certain foods; undertaking physical activities; maintaining stable a weight; and smoking or not smoking. All of these factors can influence the pathway of disease formation, which in one sense is a good thing, because it offers hope that we might be able to make a difference.

Genetics is only a small factor in the many chronic diseases we see today. I look at genetics as being the gun, in a sense, but the trigger is the environment itself. You could even have a predisposition for a certain disease, but that does not mean that you are going to get that disease. In fact, you can do a number of things that reduce that risk. This is comforting to know.
Q: Do any essential nutrients place people at greater risk for reproductive cancers?

A: Clearly, the meat-eating population has an increased risk. The recent United Kingdom Women's Cohort Study showed that total meat intake, especially processed meats that contain nitrates and nitrites, conferred a higher risk of breast cancer.
Q: Is there anything else you would like to address?

A: A group of "super foods" out there has known value — broccoli, walnuts, blueberries — and all come from the plant-based kingdom. These foods can be easily incorporated into our daily regimens. Regardless of whether we are vegetarian, we can take advantage of these foods to help reduce the risk of disease.

Much of this has to do with antioxidants and a teeter-totter balance going on in our bodies, which is about oxidative stress and whether we tip the scale in our favor or in a way that can cause disease. This may depend on how many of these great cancer-fighting foods we add to our diet. I like the fact that we have a level of science now that has been able to identify a number of foods that have known benefits.


Interview with Tim Radak, Dr.P.H., R.D.

Tim Radak, Dr.P.H., R.D., is a Nutrition Consultant at the Cancer Project, which is part of the Physicians Committee for Responsible Medicine, located in Washington, D.C. He is also the Senior Research Manager at the Northern California Cancer Center in Fremont, California. Dr. Radak has conducted research on plant-based diets and the reduced risk of chronic diseases. 'He received his Doctorate in Public Health Nutrition from Loma Linda University in California. He has been a Registered Dietitian since 2000.

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