How Diet Affects Cancer

Diet affects cancer both directly and indirectly. Nutrients directly impact the mechanisms by which cancer cells grow and spread. They indirectly help control the cancer by changing the surrounding biochemical conditions that either encourage or discourage the progression of malignant disease. The bottom line is that what you eat can spell the difference between conquering your disease and having it rage out of control.

Here are some examples of findings from recent studies that support the importance of diet in fighting cancer:

• Diets high in fat and refined carbohydrates make you more likely to become overweight, which in turn increases your risk of tumor recurrences. (8) Obese men are at significantly greater risk of developing more aggressive prostate cancer. (9)

• Dietary fats can impair the body's anti-cancer defenses by depressing the activity of natural killer (NK) cells, while a low-fat diet markedly increases NK activity. (10,11,12) Natural killer cells play a key role in preventing metastasis.

• Obese breast cancer patients are two to four times more likely to experience a recurrence than women of normal weight. (13)

For every additional 10 percentage points of calories derived from fat in the diet of newly diagnosed breast cancer patients -- by going from 25 percent to 35 percent of calories from fat -- the risk of recurrence approximately doubles. (14) An increase of 10 percentage points is alarmingly easy: just add four ounces of beef, four ounces of mozzarella cheese (about the size of three nine-volt batteries), a cup of ice cream, or four pats of butter to your daily intake and you're there.

High intake of many dietary fats is linked with higher rates of cancer recurrence, lower rates of survival, or both. (15) At the American Society of Clinical Oncology meeting in 2005, I listened to a stunning presentation of a randomized controlled study of 2,400 breast cancer patients. It found that those who adopted a diet in which 20 percent of the calories came from fat (the US norm is more like 35 percent) had a 24 percent lower rate of relapse. The lowered risk of relapse was particularly great for the 42 percent of women with the more dangerous estrogen-receptor-negative breast cancers. Because these women have fewer good conventional options, this is an especially important finding. (16)

Despite this overwhelming evidence for the benefits of a healthy diet when you are fighting cancer, that is not what mainstream medicine recommends. Yes, when it comes to cancer prevention, the American Cancer Society recommends a diet that is heavy on fruits, vegetables, whole grains and low-fat proteins while restricting unhealthy fats, refined carbs and fatty red meats. So far, so good. Yet the standard advice for patients with cancer -- that is, those for whom prevention didn't work -- is "all you can eat." (17)

Cancer patients are told to get all the calories they can, from butter, margarine, high-fat dairy products, mayonnaise, eggs, meat, hard and soft cheese, ice cream and peanut butter. The rationale is that a fat- and calorie-packed diet prevents or combats cachexia, the "starvation response" seen in cancer patients. It does not. But this response is hardly universal; only some patients become cachectic, and only at certain points in their treatment. The reality is that there are far more patients for whom "all you can eat" is exactly the wrong prescription: it makes them fill their plates with animal protein, saturated fats, unhealthful omega-6 fats and refined carbohydrates, all of which have tumor-promoting properties. (18) In fact, a 2007 study reported in the Journal of the American Medical Association found that stage III colon cancer patients who ate the least meat, fat, refined grains and desserts had half the mortality risk of those who ate the most of these foods. (19)

I don't want to pick on mainstream cancer groups -- in my five years as vice president of the uptown Chicago chapter of the American Cancer Society (ACS), I saw firsthand the good intentions of everyone involved. Nonetheless, the disconnect between the ACS's cancer-prevention dietary advice and its cancer-fighting dietary advice is hard to justify. Even laypeople can see that. A number of my patients have said to me, "My doctor used to advise that I should eat fruits and vegetables and avoid too much meat and fat so I wouldn't get cancer. Now that I got a diagnosis of cancer, I'm supposed to eat cheesecake, milk shakes and cream sauce. That doesn't make sense." They're right: it strains credulity to think that the very foods you are told to minimize in order to reduce your risk of developing cancer should be dietary staples once you have cancer. The cheesecake-and-cream-sauce advice also ignores the growing scientific evidence of the tumor-promoting potential of the standard American diet. To a great extent, the foods recommended for cancer prevention are also the foods that seem to suppress cancer after it's diagnosed. In most cases it is reasonable to use prevention studies as a guide for how patients should eat, especially in cancers where healthy diets reduce risk.

Copyright 2009 Keith I. Block, M.D.

REFERENCES AND RESOURCES

8. Bray GA, Popkin BM. Dietary fat intake does affect obesity: American Journal of Clinical Nutrition. 68(6):1157-73, 1998

9. Freedland SJ, Platz EA. Obesity and prostate cancer: making sense out of apparently conflicting data. Epidemiol Rev. 2007;29:88-97.

10. Hebert JR. Barone J. Reddy MM. Backlund JY. Natural killer cell activity in a longitudinal dietary fat intervention trial. Clinical Immunology & Immunopathology. 1990; 54(1):103-16

11. Malter M. Schriever G. Eilber U. Natural killer cells, vitamins, and other blood
components of vegetarian and omnivorous men. Nutrition & Cancer. 1989; 12(3): 271-8

12. Vujanovic NL. Basse P. Herberman RB. Whiteside TL. Antitumor functions of natural killer cells and control of metastases. Methods (Duluth). 9(2):394-408, 1996

13. Hebert JR. Augustine A. Barone J. Kabat GC. Kinne DW. Wynder EL. Weight, height and body mass index in the prognosis of breast cancer: early results of a prospective study. Int J Cancer. 1988; 42(3):315-8

14. Holm LE. Nordevang E. Hjalmar ML. Lidbrink E. Callmer E. Nilsson B. Treatment failure and dietary habits in women with breast cancer. Treatment failure and dietary habits in women with breast cancer. J Nat Cancer Inst. 1993; 85(1):32-6

15. Gregorio DI. Emrich LJ. Graham S. Marshall JR. Nemoto T. Dietary fat consumption and survival among women with breast cancer. J Nat Cancer Inst. 1985 ; 75(1):37-41

16. Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, Goodman MT, Giuliano AE, Karanja N, McAndrew P, Hudis C, Butler J, Merkel D, Kristal A, Caan B, Michaelson R, Vinciguerra V, Del Prete S, Winkler M, Hall R, Simon M, Winters BL, Elashoff RM. Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study. J Natl Cancer Inst. 2006; 98(24):1767-76.

17. Brown J, Byers T, Thompson K, Eldridge B, Doyle C, Williams AM. Nutrition during and after cancer treatment: a guide for informed choices for cancer patients. CA Cancer J Clinic 2001; 51:153-81.

18. Anon. Eating hints for cancer patients: before, during and after treatment. Available at: http://www.cancer.gov/cancertopics/eatinghints/page7#F6. Accessed May 4, 2008.

19. Meyerhardt JA, Niedzwiecki D, Hollis D, Saltz LB, Hu FB, Mayer RJ, Nelson H, Whittom R, Hantel A, Thomas J, Fuchs CS. Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA. 2007 Aug 15;298(7):754-64.