The Role of Food and Nutrition in Cancer

This article is contributed by my friend and colleague, Dr. Ricardo Parker, who has worked in cancer research for 25 years and began his career as a Research Fellow and subsequently Staff Fellow at the National Cancer Institute in Bethesda, MD.

Cancer and Nutrition

Nutrition is the relationship of foods to the health of the human body, and plays a fundamental role in either promoting health or contributing to the development of various chronic diseases, including cancer. Cancer is currently the number two cause of mortality in the United States, trailing only heart disease. Cancer is a disease of the genes, and is manifested by uncontrolled growth of cells. While only a small proportion (3-5%) of cancers is inherited, it is becoming increasingly clear that the influence of diet along with other environmental factors – both external (e.g., chemicals, radiation, viruses) and internal (e.g., hormonal imbalances, immune impairment, body composition, inherited genetic mutations, etc.) account for 75% to 80% of cancer cases and deaths in the US, with about 45% of cancers being influenced by a combination of nutrition, physical activity, and obesity (1-4) – all factors that can be modified.

Over the past 2 decades in developed countries, there has been a steady shift in the major causes of disease and death toward chronic diseases such as cardiovascular disease and cancer. Interestingly, these disease trends are becoming more and more associated with an increasingly overweight and sedentary population. Do you think diet and lifestyle might be the common link?

Certain dietary patterns are now known to be associated with risks for a number of diseases, including cancer. In 1994, the China Study was published which showed significant associations between diet, lifestyle and disease (2-5). This was a 20-year comprehensive study involving over 6,500 native-born Chinese adults (87% of Han ethnicity) covering 65 counties in 24 geographically different provinces of (mostly rural) Mainland China and Taiwan. The study revealed two basic findings: (1) people who had diets ranging from rich to very rich in plant-based foods were the healthiest and virtually devoid of chronic diseases including cancer; and (2) those who had diets ranging from rich to very rich in animal-based foods had high rates of diabetes, coronary heart disease, and increased occurrences of seven of the most common cancers in China – cancers of the colon, lung, breast, childhood brain, stomach, liver, and leukaemia (6, 7). This distinction offers an opportunity to compare China’s dietary experiences and health consequences to that of the so-called Standard American Diet (SAD) – a very rich animal-based “diet of affluence” that consists of primarily meats and dairy products.

There is no longer any doubt that the SAD diet (comprised of 40 to 50% fat; most of which is saturated fat obtained from consumption of animal-based foods – primarily meats and dairy products) has contributed to the development of chronic diseases that afflict a significant proportion of the US population, including our children. In addition, consumption of certain non-nutrients and preservatives in food, as well as certain vitamin and mineral supplements appear to also contribute to conditions that can increase risk for the four most common cancers in the US – colorectal, breast, prostate, and lung cancers. We will take a closer look at the relationship between diet and risk factors associated with three of these; cancers of the colon, breast and prostate.

Nutrition and Cancer will be presented in two parts. This article is Part I: Colorectal Cancer; and Part II: Breast and Prostate Cancers will be published subsequently.

Colorectal Cancer
Colorectal cancer is the third most common cancer in the US, affecting about 1 person in 20, and constituting 15% of all newly diagnosed cancers (1). It generally starts in the colon or rectum as a polyp (adenoma) and, slowly over a period of several years becomes an adenocarcinoma. Removing the polyp early prevents it from becoming cancer. This is why colonoscopies (at 50 years and periodically thereafter) are so important. Since this cancer occurs within the digestive system, both risk and prevention are related to diet. In fact, the November 2007 Food, Nutrition and the Prevention of Cancer: A Global Perspective report (2), which is the most comprehensive International study undertaken, involving an analysis of 7,000 research studies (such a study of studies is called a meta-analysis) by a panel of 21 experts, showed convincing evidence that the environmental factors of food, nutrition, physical activity, and body composition influence the risk for cancer. The evidence showed a direct link between excess fat and increased risk for seven different cancers including colorectal cancer, and breast cancer in post-menopausal women.

The report emphasizes that we can reduce our cancer risk through increased physical activity, increased consumption of whole plant-based foods, and decreased consumption of red meats and meats preserved by smoking, curing or salting. The experts were in particular agreement that we should eliminate from our diets processed meats (e.g., hot dogs, sausage, bologna, etc.) because they contain nitrates and nitrites as preservatives that can be converted by the bacteria in our colon into potent cancer-causing substances called nitrosamines (8, 9). In addition, grilling, charring, broiling or frying of animal fats and proteins in meat including fish was discouraged because these activities can produce potent cancer-causing compounds called heterocyclic amines (HCA). Indeed, the typical SAD diet is very highly refined, high in animal fat and protein, and low in fiber; and is highly correlated to colon cancer.

In contrast, diets that are whole food-based, high in fiber, and consist of small amounts of animal fat and protein are associated with a very low occurrence of colon cancer (10). It is thought that dietary fiber lowers risk for digestive tract cancers by decreasing bowel transit time, which can physically decrease contact of carcinogens in the digestive tract, thus preventing them from attacking the mucosal wall of the colon. Studies show that vegetarians consume more than twice the amount of dietary fiber compared to meat-eaters, and have the least tendency to develop colon cancer, and lower risks of lymphomas and cancers of the pancreas, stomach, colon, rectum, breast, uterus, mouth, throat, liver, and thyroid (10). It is, therefore, reasonable to avoid refined and processed meats, while taking in adequate amounts of green leafy vegetables which are an excellent source of phyto(plant)nutrients, vitamins and minerals. Did you know that a single apple contains over 10,000 phytochemicals?

The known negative risk factors associated with diet, lifestyle and colorectal cancer are: a diet high in fat, especially fat from animal sources and, over time, eating a lot of red meats and processed meats; lack of exercise, especially in people who are not active; being very overweight or obese increases a person’s risk of dying from colorectal cancer; smoking – we know it causes lung cancer and increases the risk of many other cancers, but recent studies show that smokers are 30% to 40% more likely than nonsmokers to die of colorectal cancer; heavy users of alcohol are usually malnourished with chronic debilitating health that increases their risk for colorectal and other cancers; and diabetics have a 30% increased risk and tend to have a higher death rate from colorectal cancer.

Fresh fruits and vegetables are the principal whole food sources of phytonutrients, and play an important role in both prevention and protection against cancer (2). Indeed, the consumption of vegetables is more helpful in reducing cancer because they contain much higher amounts of cancer-protective compounds–especially green vegetables. Among these green vegetables, the cruciferous family has demonstrated the most dramatic protection against cancer (11-14). Cruciferous vegetables (broccoli, Brussels sprouts, cabbage, cauliflower, kale, bok choy, collards, arugula, and watercress) contain a symphony of phytonutrients with potent anti-cancer effects, which appear to play a protective role by lowering the risk for cancers of the mouth, pharynx, larynx, esophagus, and stomach. Researchers have identified a number of phytochemicals in cruciferous vegetables (i.e., glucosinolates, crambene, indole-3-carbinol and isothiocyanates [products of enzymatic breakdown of glucosinolates]) that have been shown to help control critical enzyme systems in the body that defend against cancer; and have the ability to stop the growth of cancer cells, including tumors of the breast, cervix, endometrium, lung, liver and colon. These compounds also appear to play a protective role against prostate cancer (13, 14).

Evidence is mounting that the minerals, vitamins and phytochemicals in plant foods interact to provide extra cancer protection. This concept is called synergy. In addition, vegetables, fruits, whole grains and beans are low calorie, high nutrient foods that help to protect against weight gain, especially since being overweight or obese is implicated in the development of certain types of cancer. Eating a predominantly plant based diet can help prevent weight gain and therefore protect against cancer risks that are convincingly increased by higher body fat – namely cancers of the colorectum, esophagus, endometrium, pancreas, kidney, and breast in postmenopausal women. The current general recommendation is that at least 2/3 of your plate should be filled with vegetables, fruit, whole grains and beans.

© Ricardo J. Parker, M.S., Ph.D.
Department of Pediatrics,
Loma Linda University Health Care,
Loma Linda, CA 92350, USA.

Adventist Health Ministry,
Laguna Niguel, CA 92677, USA.

References

1. Cancer Facts and Figures 2007. American Cancer Society. www.cancer.org/downloads/STT/CAFF2007PWSecured.pdf

2. World Cancer Research Fund/American Institute for Cancer Research (2007) Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective. AICR, Washington DC, pp. 516. http://www.dietandcancerreport.org/

3. Chen, J. et al. (1991) Diet, Lifestyle and Mortality in China. A Study of the Characteristics of 65 Chinese Counties. Oxford, UK; Ithaca, NY; Beijing, PRC: Oxford University Press.

4. Medical Publishing House (1990); Campbell, T.C. and Chen, J. Diet and Chronic Degenerative Diseases: Perspectives from China.” Am. J. Clin. Nutr. 59 (Suppl.) 1152S-1161S, 1994.

5. Campbell, T. C. (1994) The Dietary Causes of Degenerative Diseases: Nutrients vs. Foods. In: N. J. Temple and D. P. Burkitt (Eds), Western Diseases: Their Dietary Prevention and Reversibility, pp 119-152. Totowa, NJ: Humana Press.

6. Campbell, T. C. and Chen, J. (1994) Diet and Chronic Degenerative Diseases: A Summary of Results from an Ecologic Study in Rural China. In: N. J. Temple and D. P. Burkitt (Eds), Western Diseases: Their Dietary Prevention and Reversibility, pp 67-118. Totowa, NJ: Humana Press.

7. Campbell T. C. et al. (1992) China: From Diseases of Poverty to Diseases of Affluence. Policy Implications of the Epidemiological Transition. Ecol. Food Nutr. 27: 133-144.

8. Bartsch, H. and Montesano, C. (1984) Relevance of Nitrosamines to Human Cancer. Carcinogenesis, Vol.5 no.ll. pp. 1381 -1393.

9. Article 15: Minerals Matter. The Wrong Amount Can Harm You. Consumer Report on Health. Vol. 18, No. 6. June 2006, pp1, 4-6. In: Annual Editions. Nutrition 07/08, 19th Edition. D. Klimis-Zacus, ed. McGraw Hill. pp. 60-62, 2008.

10. Jacobs, D. R. Jr. et al. (1998) Whole-Grain Intake and Cancer: An Expanded Review and Meta-Analysis. Nutr. Cancer 30: 85–96.

11. Seow, A. et al. (2002) Dietary Isothiocyanates, Glutathione S-Transferase Polymorphisms and Colorectal Cancer Risk in the Singapore Chinese Health Study. Carcinogenesis 23(12): 2055-261.

12. Steinkellner, H. et al. (2001) Effects of Cruciferous Vegetables and Their Constituents on Drug Metabolizing Enzymes involved in the Bioactivation of DNA-Reactive Dietary Carcinogens. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis Vols. 480-481: 285-297.

13. Singh, S. V. et al. (2005) Sulphoraphane-Induced Cell Death in Human Prostate Cancer Cells is initiated by Reactive Oxygen Species. J. Biol. Chem. 280(20):19911-19924.

14. Xiao, D. et al. (2003) Allyl Isothiocyanate, a Constituent of Cruciferous Vegetables, inhibits Proliferation of Human Prostate Cancer Cells by causing G2/M Arrest and Inducing Apoptosis. Carcinogenesis 24(5):891-897.