Fruits and vegetables provide only modest protection from cancer?

vegetables

 

You’ve probably seen these headlines on the internet or television recently, claiming that fruits and vegetables provide very little protection against cancer. Of course something like this makes big news – it makes eaters of the typical Western diet feel validated in their unhealthy choices. But is it true? Do fruits and vegetables really offer only weak protection against cancer? Let’s look at the details of the study.

Researchers analyzed data from the European Prospective Investigation into Cancer and Nutrition (EPIC), a large study of over 400,000 people. Subjects reported dietary intakes and were followed for approximately 8 years. The researchers reported the associations between fruit and vegetable intake and risk of total cancer. Two-hundred grams of combined fruits and vegetables (approximately 2 servings) offered a 3% decrease in risk that was statistically significant.1 

According to the lead scientist, Dr. Paolo Boffetta, from Mount Sinai Medical Center, “The bottom line here is that, yes, we did find a protective effect of fruit and vegetable intake against cancer, but it is a smaller connection than previously thought. However, eating fruits and vegetables is beneficial for health in general and the results of this study do not justify changing current recommendations aiming at increasing intake of these foods.”2

A tiny amount of plant food offers a tiny amount of benefit.

Yes, 3% is a tiny reduction in risk – but 200 grams is also a tiny amount of fruits and vegetables! One medium apple is approximately 180 grams, one cup of blueberries is 150 grams, and 1 cup of chopped raw broccoli is 90 grams. So keep in mind all these people did is eat the standard cancer-causing diet and add one apple or two cups of vegetables with dinner, they did not follow a vegetable-centered diet. They were still eating all the cancer-causing processed foods and animal products as their major source of calories.

The median daily intake in this study was 335 grams of fruits and vegetables combined per day – only about three servings. According to the CDC, only one-third of U.S. adults eat two or more servings of fruit per day, and only one-quarter of adults eat three or more servings of vegetables per day.3 These minimal amounts cannot be expected to provide disease protection. I recommend a far more substantial intake of fruits and vegetables with 90 percent of calories coming from nutrient rich plant material, lots of it raw and green. I recommend about two pounds of vegetables per day (approximately 900 grams) and at least 4 fresh fruits per day (which adds another 600 grams). Most importantly, attention should be paid to the highly cancer-protective plant foods, greens, onion, berries, beans and seeds. 

The more fruits and vegetables the subjects ate, the more cancer protection they got.

Many of the news stories on this subject neglected to mention the fact that the researchers found a dose-response relationship between fruit and vegetable intake and cancer risk – this means that as the number of servings increased, rates of cancer decreased. Those eating five servings per day reduced their risk by 9% compared with those eating 2.5 or less, and those eating more than eight servings per day reduced their risk by 11%.4 The benefits of lifestyle changes are proportional to the changes made. As we add more vegetable servings, we increase our phytochemical intake and leave less room in our diet for harmful foods, enhancing cancer protection even further. 

Different fruits and vegetables offer different levels of protection.

In this study, all fruits and vegetables were lumped together in one category – this could have diluted the results. Leafy greens and potatoes have nutrient profiles that are quite different, but in this study, they are both treated the same.   The participants did not eat an extra 200 grams of raw greens - French fries and ketchup counted as a vegetable.

Cruciferous vegetables, such as kale, cabbage, collards, and broccoli, contain potent chemopreventive compounds called isothiocyanates (ITCs). ITCs have a variety of anti-cancer actions including inhibition of angiogenesis (blood vessel formation; important for tumor growth), detoxification or removal of carcinogens, inhibition of cancer cell growth, promotion of cancer cell death, and prevention of DNA damage by carcinogens. Epidemiological studies suggest that cruciferous vegetables, onions, and mushrooms are far more protective against cancer than vegetables overall - inverse relationships between cruciferous vegetable intake and breast, prostate, lung, and colorectal cancers have been found.5  For example, in one prospective study, one or more servings per week of cabbage reduced the risk of pancreatic cancer by 38%.6 And that was just one serving a week, demonstrating dramatic protection is available and real when a diet is ideally designed. The regular consumption of mushrooms has been demonstrated to decrease risk of breast cancer by over 60 percent.7 Onions, berries, seeds and beans also have dramatic beneficial effects.8 In other words, high nutrient plant foods work synergistically and a well designed diet can offer dramatic protection against not just cancer, but heart disease, strokes and dementia.

Healthful eating is a lifetime commitment

The EPIC study followed adult subjects for 8 years, but the foundation of adult cancers was very likely laid down in childhood or early adulthood.9   These researchers missed the most important tenet of nutritional research and that is—childhood diets are the major cause of adult cancers. I wrote a book about this—Disease-Proof Your Child, with all the supporting scientific references. The protective substances contained in fruits and vegetables are more effective if they are consistently present in the diet since childhood.  Making moderate changes later in life, like adding a serving of fruit and vegetables, is not likely to make much of an impact on cancer risk. For later life changes to dramatically reduce cancer risk a total dietary makeover is required, that is one of the purposes of my nutritarian diet-style, to offer people real protection from an ideally designed diet that is adopted later in life.

Conclusion

Most people are confused about nutrition, and results like these can add to the confusion. There is clear evidence that unrefined plant foods protect against chronic disease, but modest nutritional improvements offer only modest health benefits. Cutting back on cigarettes does not offer much protection against lung cancer either.  It is the total package of a well-designed, nutrient-dense diet, regular exercise, and a healthy weight that offers optimal benefit. We can win the war on cancer.

 

References:

1. Boffetta P, Couto E, Wichmann J, et al. Fruit and Vegetable Intake and Overall Cancer Risk in the European Prospective Investigation Into Cancer and Nutrition (EPIC). J Natl Cancer Inst. 2010 Apr 6.[Epub ahead of print]

2. Mount Sinai Study Shows Only a Weak Link Between Fruit and Vegetable Intake and Reduced Risk of Cancer. http://mountsinai.org/about-us/newsroom/press-releases/mount-sinai-study-shows-only-a-weak-link-between-fruit-and-vegetable-intake-and-reduced-risk-of-cancer

3. U.S. Centers for Disease Control. Fruit and Vegetable Consumption Among Adults --- United States, 2005. Morbidity and Mortality Weekly Report March 16, 2007 / 56(10);213-217

4. NewScientist. Short Sharp Science: Five fruit and veg a day won't keep cancer away. http://www.newscientist.com/blogs/shortsharpscience/2010/04/five-fruit-and-veg-a-day-wont.html

5. Higdon JV et al. Cruciferous Vegetables and Human Cancer Risk: Epidemiologic Evidence and Mechanistic Basis. Pharmacol Res. 2007 March ; 55(3): 224–236

6. Larsson SC, Hakansson N, Naslund I, Bergkvist L, Wolk A. Fruit and vegetable consumption in relation to pancreatic cancer: a prospective study. Cancer Epidemiol Biomarkers Prev 2006;15:301–305.

7. Zhang M, et al. Dietary intakes of mushrooms and green tea combine to reduce the risk of breast cancer in Chinese women. Int J Cancer. 2009;124:1404-1408

8. Powolny AA, Singh SV. Multitargeted prevention and therapy of cancer by diallyl trisulfide and related Allium vegetable-derived organosulfur compounds. Cancer Lett. 2008 Oct 8;269(2):305-14.

Stoner GD, Wang LS, Casto BC. Laboratory and clinical studies of cancer chemoprevention by antioxidants in berries. Carcinogenesis. 2008 Sep;29(9):1665-74.

Aune D, De Stefani E, Ronco A, et al. Legume intake and the risk of cancer: a multisite case-control study in Uruguay. Cancer Causes Control. 2009 Nov;20(9):1605-15.

Jenab M, Ferrari P, Slimani N, et al. Association of nut and seed intake with colorectal cancer risk in the European Prospective Investigation into Cancer and Nutrition. Cancer Epidemiol Biomarkers Prev. 2004 Oct;13(10):1595-603.

9. Maynard M, Gunnell D, Emmett P, Frankel S, Davey Smith G. Fruit, vegetables, and antioxidants in childhood and risk of adult cancer: the Boyd Orr cohort. JEpidemiol Community Health. 2003 Mar;57(3):218-25. Erratum in: J Epidemiol Community Health. 2007 Mar;61(3):271.

Fuemmeler BF, Pendzich MK, Tercyak KP. Weight, Dietary Behavior, and Physical Activity in Childhood and Adolescence: Implications for Adult Cancer Risk. Obes Facts. 2009;2(3):179-186.

Vitamin D may protect against colon cancer

Vitamin D insufficiency is widespread, and is now thought to contribute to a variety of disease states, including osteoporosis, cardiovascular disease, diabetes, autoimmune diseases, depression, and cancers.

Vitamin D affects calcium absorption and metabolism in the bone, kidney, and intestine, but it also acts as a regulator of gene transcription in many tissues, affecting genes that control cell growth, adhesion, differentiation, proliferation, and programmed cell death. Vitamin D’s action on such genes has been shown to suppress proliferation of human colon cancer cells and tumor growth.1,2

Also, the cells of the colon, whether they are normal or cancerous, are capable of converting 25(OH)D to its active form 1,25(OH)2D. It is likely that this ability has purpose – vitamin D may have yet unidentified actions specific to the cells of the colon.

Colon

Researchers analyzed data from the European Prospective Investigation into Cancer and Nutrition (EPIC) study, which has over 520,000 participants. Blood levels of vitamin D, which were measured at the start of the study, were compared between 1248 colorectal cancer patients and matched controls after diagnosis.

Circulating 25(OH)D levels of below 20 ng/ml were associated with increased risk of colorectal cancer compared with levels between 20-30 ng/ml.  When the researchers arranged the data into 5 quintiles of Vitamin D levels, they found a dose-dependent reduction in colon cancer risk; highest quintile (greater than 40 ng/ml) had 40% reduced risk compared to lowest quintile (less than 10 ng/ml). When cancers were distinguished by site, the association between Vitamin D levels and colon cancer was even stronger – the highest quintile showed a 60% risk reduction.3

This is the largest study on the subject to date, following up at least 25 previous studies since 2002. A 2009 review of these previous studies confirmed that there is indeed an inverse relationship between vitamin D levels and colorectal cancer. Even after a diagnosis of colon cancer, vitamin D levels are associated with increased survival – in colon cancer patients, higher vitamin D levels were predictive of a decreased risk of death from any cause, not only colon cancer.4

The 2009 review concluded that 25(OH)D levels of 32 ng/ml would be sufficient to achieve the protection against colorectal cancers seen in the literature, and the current study saw benefits with as low as 20 ng/ml. A minimum of 30 ng/ml 25(OH)D is thought to be required for vitamin D to properly exert its many beneficial effects.5 Accordingly, I  recommend that levels be maintained in the range of 35-55 ng/ml. 

About 50% of the U.S. population is deficient in vitamin D and cannot rely on sun exposure because of indoor jobs, skin color, and their climate. Plus, with the depletion of the ozone layer, the amount of sun most people would require to achieve these levels may result in too much skin damage and skin cancer.6 

 

 References:

1. Ingraham BA, Bragdon B, Nohe A. Molecular basis of the potential of vitamin D to prevent cancer. Curr Med Res Opin. 2008 Jan;24(1):139-49.

2. Journal of Clinical Investigation (2009, July 7). Understanding The Anticancer Effects Of Vitamin D3. ScienceDaily. Retrieved April 6, 2010, from http://www.sciencedaily.com /releases/2009/07/090706171500.htm

Emory University (2008, April 14). Vitamin D And Calcium Influence Cell Death In The Colon, Researchers Find. ScienceDaily. Retrieved April 6, 2010, from http://www.sciencedaily.com /releases/2008/04/080413161052.htm

Rockefeller University Press (2008, November 26). Vitamin D Can Alter Color Cancer Cells In Many Ways, Through One Pathway. ScienceDaily. Retrieved April 6, 2010, from http://www.sciencedaily.com /releases/2008/11/081117091614.htm

3. Jenab M, Bueno-de-Mesquita HB, Ferrari P, et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations:a nested case-control study. BMJ. 2010 Jan 21;340:b5500.

High vitamin D levels linked to lower risk of colon cancer. ScienceDaily. Retrieved April 6, 2010, from http://www.sciencedaily.com /releases/2010/01/100122002340.htm

4. Dana-Farber Cancer Institute (2008, June 20). Vitamin D Linked To Colon Cancer Survival. ScienceDaily. Retrieved April 6, 2010, from http://www.sciencedaily.com /releases/2008/06/080619090749.htm

5. Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences.Am J Clin Nutr 2008;87(suppl):1080S– 6S.

6. Terushkin V, Bender A, Psaty EL, et al. Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes. J Am Acad Dermatol. 2010 Apr 2. [Epub ahead of print]