Keeping Cancer at Bay with Diet

Cancer is stubborn; ask anyone who’s had it. You hope it’s gone for good and then it comes back. But thanks to advances in medicine and early detection, the future is much rosier than it used to be for cancer victims. The cancer death rate in this country has declined steadily since the 1990s. The overall survival rate for all cancers for five years is about 65 percent, even more for breast and prostate cancers. There are now over 12 million survivors in the U.S.—most looking at a variety of strategies to help keep cancer at bay. EN explores the latest science on lifestyle factors that help prevent cancer recurrence.

What causes cancer? According to the American Institute for Cancer Research (AICR), cancer is not a single disease with a single cause—there’s more to it than eating a poor diet or getting fat. Other contributors include environmental factors like pollutants, radiation and toxic contaminants, smoking, gene variants, age, and certain infections. Still, it is estimated that approximately one-third of cancer deaths in the U.S. are related to poor nutrition, physical inactivity and excess weight—all modifiable risk factors.

Does it matter if you’re fat? Yes, it does—for all cancers. According to the National Cancer Institute, obesity is related to increased risk for cancers of the colon, uterus, kidney, esophagus, stomach, breast, gallbladder, ovaries and pancreas; 14 percent of deaths from cancer in men and 20 percent in women are due to overweight or obesity. According to David Heber, M.D., Ph.D., professor of medicine at UCLA Center for Human Nutrition, there is a clear association between obesity and cancer risk, incidence, or progression for a number of common forms of cancer. A 2006 article in Obesity Reviews reported that there is enough evidence to suggest that weight management should be part of the strategy to prevent the occurrence, recurrence and death risk of breast cancer.

Diet-cancer connections. Diet accounts for 25 percent of cancers in developed countries, according to a 2011 review published in European Journal of Cancer Care. But is it what we eat or what we don’t eat that is to blame? The body of scientific research on dietary patterns and cancer is intriguing.

In a 2007 study published in the Journal of the American Medical Association, researchers observed 1,009 patients for two years, and discovered that a Western diet pattern (high intake of meat, fat, refined grains, and desserts) after cancer diagnosis was associated with a significantly worse risk of disease-free survival, cancer recurrence, or death. The Women’s Healthy Eating and Living Study (Journal of the American Medical Association, 2007), a randomized controlled seven-year study that examined whether a diet high in vegetables, fruit and fiber and low in fat could have an impact on cancer survival after treatment for early stage breast cancer, showed that eating five to seven servings/day of fruits and vegetables did not reduce additional breast cancer events or death in study subjects. In contrast, the Women’s Intervention Nutrition Study, a long-term randomized study, found a 24 percent reduction in risk of breast cancer recurrence for women on a low-fat diet. 

Most studies on preventing first cancers show a strong relationship between prevention and eating a diet high in fruits and vegetables, while red meat seems to increase cancer risk. Demark-Wahnefried, Ph.D., R.D., associate director, University of Alabama Comprehensive Cancer Center, says, ”There is less convincing evidence against red meat than before, but people definitely should not be grilling or charring the meat, and we still recommend against processed meats.” Scientists don’t have all the answers yet, although they continue to recommend a diet high in fruits, vegetables and whole grains, and low in fat and refined carbohydrates to reduce cancer risk.

Sugar and cancer scenario. You might have read that sugar “feeds cancer cells.” To most of us, sugar is that white granulated stuff we use to sweeten our foods. But in this case, sugar really means glucose found in blood. Cancer cells use a lot of glucose, so high blood glucose, which is promoted by overweight and refined carbohydrate intake, could contribute to first and recurring cancer risk. People who are overweight may have a condition called insulin resistance that results in higher than normal circulating insulin levels, which can help cancer cells consume glucose and grow.

Because of the glucose/cancer relationship, there has been interest in using the Glycemic Index (GI,) a system that ranks carbohydrate foods according to their effect on blood glucose, to treat cancer survivors. Scientists reported in the 2009 issue of Journal of American College of Nutrition that the GI might be a useful tool for management of body weight and associated chronic diseases, including cancer. But, to date, the research results of GI on cancer risk have been conflicting. One of the problems is that people who eat high-GI foods (those that raise blood sugar the most) likely eat less fruits, vegetables and whole grains, so it’s difficult to know whether it’s the high-GI diet or the poor diet in general that promotes cancer recurrence.

Do supplements help? Dietary supplements or single nutrients, including vitamin D, omega-3 fatty acids, selenium, calcium, resveratrol, fiber, and antioxidants like vitamins E and C, as well as food components like soyfoods, coffee, garlic, green tea, cruciferous vegetables (i.e., broccoli and cabbage,) berries, flax, grapes, and spices are under study to see if they can keep cancer survivors healthy longer. To date, however, there are no solid recommendations for using supplements to ward off future cancers, even though as many as 80 percent of cancer survivors report taking supplements during their treatment and recovery.

Remember, more is not always better. Antioxidants like vitamins C and E that protect healthy cells might also protect cancer cells from destruction by cancer treatments. Soy has been shown to be protective in some cases, but in women with estrogen-dependent cancers, large amounts are controversial because of soy’s plant estrogen compounds. AICR recommends against using supplements to prevent cancer. According to Karen Collins, M.S., R.D, C.D.N., nutrition advisor to AICR, the only exception might be vitamin D, but she cautions that more research is needed to clarify dosage recommendations.

Surviving chronic disease. Those who survive cancer are at higher risk for having a second cancer, as well as other chronic diseases, such as heart disease and diabetes, due to genetic factors and as a consequence of treatment, according to Demark-Wahnefried. Diana Dyer, M.S., R.D., author and expert known as the “cancer dietitian,” says that she emphasizes the importance of making diet choices that improve your general health and well-being, as well as reduce the risk of chronic diseases that may be a result of cancer therapy. AICR strongly advises cancer survivors to include physical activity along with a balanced, plant-based diet in their health maintenance routine in order to reduce the risk of heart disease and diabetes.

Bottom line. “One thing’s for sure; there are no easy or obvious magic bullets with nutrition, foods and dietary supplements,” says Dyer. The recommendations for preventing heart disease and diabetes are really no different from those for preventing cancer: eat smart, move more, and stay lean. Collins suggests, “Focus first on priorities of aiming to reach a weight that is healthy and achievable.” She recommends that you emphasize regular exercise and eating fruits and vegetables; then, if you’d like to add some new nutritional strategies like drinking green tea, go ahead. 

—Sharon Salomon, M.S., R.D.

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