Title: Cancer & Diet

Key words: carcinogenesis, dietary influences, anti-carcinogenic, antioxidant properties, unsaturated fats, phenols, tannins, flavenoids, isothiocyanates, isoflavones, polyphenols,

Date: Feb 1999

Category: 13. Specific conditions

Type: Article

Author: Dr van Rhijn

 

 

Cancer & Diet

Reducing Cancer Risk Through Diet

 

 

Introduction

Cancer accounts for 25% of all deaths in the UK1, and this proportion is still increasing especially among females2,3. The development of cancer (carcinogenesis) involves a multi-stage process4, and although genetic factors influence individual predisposition to cancer development, there is a growing body of evidence to suggest that environmental factors (80%5) are responsible for a large proportion of cancers. This paper briefly discusses the evidence for the role of dietary (70%6) influences in protecting against the long-term risk of cancer.

Dietary Influence

Compelling chemical, biochemical, epidemiological7,8 and clinical experimental data suggest that diet as a whole, and specific nutrients (fat, protein, vitamins and minerals) as well as non-nutrient components (phenols, tannins, flavenoids and isothiocyanates), have a role to play in protection against cancer. Numerous other plant constituents (lignans, phytoestrogens9, glucosinolates, indoles, allium compounds, phytic acid, sterols and saponins) have been shown to be anti-carcinogenic. It has been postulated that part of the protective effect is due to the antioxidant properties of certain nutrients (b -carotene, vitamins C & E, zinc and selenium10) and various studies11 show an inverse correlation with cancer incidence12.

Some Research Evidence

Although the relationship between antioxidants and cancer risk in humans remains uncertain13, there is some supportive evidence that dietary carotenoids and vitamin C may be inversely related to the risk of lung, upper digestive tract and uterine cervical cancers14. Soluble and insoluble non-starch polysaccharides (NSP) diets are associated with lowering colorectal and endometrial, and green tea (polyphenols) with lowering esophageal 15 cancer risk. Unsaturated fats in fish oils16 may protect against breast and colorectal cancer. Soy (isoflavones), grains and vegetables with woody stems (precursors to lignans) and diphenolic phytoestrogens17, 18, of (lignans and isoflavonoids) are plausibly associated with a lower risk of sex-hormone-related cancers 19.

Higher consumption of meat and dairy products has been associated with greater risk of prostate cancer; red meat consumption with risk of colon cancer, and also lifetime excessive energy intake20 with an increased risk of human cancer. Potential carcinogens (fungal contamination, cooking or tobacco) and cancer promoters (salt and alcohol) elevate the overall risk of cancer (epithelial).

Suggested Foodstuffs

Fruit and vegetables21 are the principal sources of the majority dietary antioxidants, together with grains, which also provide NSP. It is suggested22 that we should consume greater amounts of raw and fresh, leafy green or colourful vegetables (carotenes & lycopenes), fruit (including tomatoes and citrus fruit). Biologically active compounds (isoflavonoids and lignans) are present in soybean products as well as whole grain cereals, seeds and probably berries and nuts (lignans). Avoid high intakes of red meat, foods high in animal fat (replace with unsaturated fatty acids). Avoid excessive sugar, alcohol and nicotine.

Conclusion

The WHO advises at least 500g/day of fresh fruit and vegetables.This is endorsed by the UK advocating at least 5 servings a day. Consuming an abundance of fruits and vegetables will substantially reduce the risk of human cancer without having to resort to supplements.

 

References

1. OPCS,. Office of Population Censuses and Surveys. Mortality Statistics, cause. Series DH2, No. 18. 1993; London: HMSO.

2. Lancet Editorial.. The cancer epidemic: fact or misinterpretation? Lancet 1992; 340, 399 400.

3. Adami, H-O, et al.. Increasing cancer risk in younger birth cohorts in Sweden. Lancet 1993; 341. 773 777.

4. Singh, V.N. and Gaby, S.K.. Premalignant lesions: role of antioxidant vitamins and B-carotene in risk reduction and prevention of malignant transformation. American Journal of Clinical Nutrition 1991; 53, 586S 590S.

5. Higgens, J.. Environmental Carcinogenesis Cancer Supplement 1993; 72, 971 977.

6. Doll, R.. An overview of the epidemiological evidence linking diet and cancer. Proceedings of the Nutrition Society 1990b; 49, 119 131.

7. Kromhout, D. at al.. Contribution of epidemiology in elucidating the role of foods in cancer prevention. In: Waldron, K.W. et al (eds). Food and Cancer Prevention: Chemical and Biological Aspects. 1993; Cambridge: Royal Society of Chemistry, pp 24 36.

8. UK Nutritional Epidemiology Group.. Diet and Cancer. A review of the epidemiological literature, prepared for the Nutrition Society. 1993; London: Nutrition Society.

9. Cline JM and Hughes C.L. Jr. Phytochemicals for the prevention of breast and endometrial cancer. Cancer Treat Res, 1998, 94:, 107-34

10. Clark, L.C. et al.. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. J. Am. Med. Assoc. 1996; 276: 1957 1963.

11. Rice-Evans, C. and Miller, N. J.. Antioxidants the case for fruit and vegetables in the diet. Br. Food J. 1995; Vol. 97 No 9. Pp. 35 40.

12. Gey, K.F.. "The relationship of antioxidant status and the risk of cancer and cardiovascular disease: A critical evaluation of observational data." In Nohl, H., Esterbauer, H. and Rice-Evans, C. ( Eds), Free Radicals in the Environment, Medicine and Toxicology, Richelieu Press, 1994; London. pp. 181219.

13. Flagg, E. W. et al.. Epidemiological studies of Antioxidants and Cancer in Humans J. Am. Coll. Nutr. 1995; Vol 14, No. 5, 419 427.

14. Byers, T. & Perry, G.:. Dietary carotenes, vitamin C and vitamin E as protective antioxidants in human cancer. Ann. Rev. Nutr. 1992; 12: 139 159.

15. Gao, Y.T. et al.. Reduced risk of esophegeal cancer associated with green tea consumption. J. Natl. Cancer Inst. 1994; 86: 855 858.

16. Cayhill, C.P. et al.. Fat, fish, fish oil and cancer. Br. J. Cancer 1996; 74: 159 164.

17. Adlercreutz, C.H.. Soybean phytoestrogen intake and cancer risk. J. Nutr. 1995; Jul; 125:3 Suppl, 757S 770S.

18. Shao, Z.M. et al.. Genistein exerts multiple suppressive effects on human breast carcinoma cells. Cancer Res. 1998; Nov, 58:21, 4851-7

19. Murkies, et al.. Clinical review 92: Phytoestrogens. J. Clin. Endocrinol. Metab, 1998; Feb, 83:2, 297-303.

20. Willett. W.C.. Nutrition and Cancer. Salud. Publica Mex. 1997; Jul, 39:4, 298 309.

21. Miller A.B. et al:. Diet in the aetiology of cancer: a review. Eur J Cancer 1994; 30A: 207-220.

22. Potter, J.D. & Steinmetz, K.. Vegetables, fruit and phytoestrogens as preventive agents. IARC Sci.Publ. 1996; 139, 61-90.

Further Reading

The Department of Health, Eat Well !:; An action plan from the Nutrition Task Force to achieve the health of the Nation targets on diet and nutrition. The Health of the Nation. HMSO, London. 1994

The Department of Health, Eat Well II: A progress report from the Nutrition Task Force on the action plan to achieve the Health of the Nation targets on diet and nutrition. HMSO, London. 1996

The National Heart Forum: At Least Five a day. Strategies to increase vegetable and fruit consumption. The Stationery Office. London. 1997

The National Heart Forum:; Preventing coronary heart disease: The Role of Antioxidants, Vegetables and Fruit. The Stationery Office. London. 1997

Trends in Patterns of Disease and Diet: Fact File No 10: 1993; National Dairy Council. London.

Vitamins Minerals and Health: Fact File No 3: 1997; National Dairy Council. London.