By Jason Bosley-Smith, MS, LDN, CNS, FDN
Cancer is perhaps the most feared chronic disease in modern times, and as Siddhartha Mukherjee designates in his seminal work, the “Emperor of All Maladies”. Perhaps rightfully so. According to statistics from the American Cancer Society, the estimated number of new cancer cases in the US in 2016 will exceed 1.6 million, and estimated cancer deaths will reach nearly 600,000.(1) To understand how we can mitigate our risk for cancer in light of these rather daunting numbers, it is helpful to first understand exactly how cancer arises in the body.
Fundamentally, cancer is a genetic disease at the cellular level, where cells become aberrant in their structure and function. DNA is damaged, tumor-suppressor genes get “turned off”, and tumor-promoter genes “turn on”. With this loss of regular, appropriate function, the cells begin to lose important biological features such as apoptosis or programmed cell death – the mechanism by which cells automatically self-destruct when they become deranged in function or damaged in structure. This is a protective mechanism for our bodies, preventing damaged cells from producing byproducts that can harm adjacent cells and from a loss of function that impairs the original purpose of that cell. Without this safeguard, cellular growth occurs that no longer responds to normal genetic controls. The cell continues to reproduce, without need for it to reproduce, depriving other cells of nutrition to fuel its own growth and replication. Eventually, these “rogue” cells can detach from surrounding cells and infiltrate or spread into surrounding tissue. Tumor cells often travel and spread to distant sites from their place of origin via the bloodstream and lymphatic vessels.
The fact that cancer initiation is the result of genetic changes may produce a sense of fatalism – that your genes control your cancer destiny – this far from the truth. While genetic changes that cause cancer can be inherited, only about 5% to 10% of all cancers result directly from gene defects (known as mutations) inherited from a parent.(2) The remaining 90-95% of cancers develop as the result of mutations caused by repeated environmental incidents that serve to damage DNA and influence gene expression. Common environmental exposures that can lead to mutations include chemicals in tobacco smoke, viruses, industrial agents, and radiation, such as ultraviolet rays from the sun.
Nutrition and Cancer
Diet is another environmental factor that can influence the potential for cancer development. Research in the area of nutrition’s impact on cancer risk is somewhat mixed and in some areas inconclusive, but there are some components of dietary habit and consumption that are clearly associated with a reduced prevalence or risk of carcinogenesis. Perhaps more importantly, there are clear distinctions between what is supported by evidence with respect to nutrition and cancer prevention versus those claims that lack solid scientific support.
Let’s examine some elements of nutrition that have been shown to carry support based on the available research.
1.) Plant-based diet.
Epidemiological data, information gathered by analysis of the patterns, causes, and effects of health and disease conditions in defined populations, supports a diet rich in vegetables and fruits as being associated with reduction in risk for cancer. More specifically, dietary intake of ≥ 5 servings or ≥ 2 ½ cups of vegetables and fruits per day is associated with a reduction in cancer incidence and cancer mortality, particularly when paired with recommended physical activity, healthy body weight, and alcohol consumption guidelines.(3) From a practical perspective, 1 serving of vegetables equals 1 cup of raw leafy vegetables (about the size of a small fist), or 1/2 cup of other vegetables.
Interestingly, some of this research also indicates a positive association with the variety of unique fruits or vegetables consumed per month; specifically, a greater proportion of foods high in carotenoids. Carotenoids are organic fat-soluble compounds that give certain fruits and vegetables their yellow, orange, or red pigments. Common dietary carotenoids include beta-carotene, lycopene, lutein and zeaxanthin whose beneficial effects are thought to be due to their role as antioxidants.(4) Fruits and vegetables that provide significant amounts of carotenoids include carrots, watermelon, papayas, tomatoes, squash, pink grapefruits and pumpkins.(5)
To ensure optimal protection, set a goal of consuming 1 cup of plant-based foods to each your 3 main meals each day, including a variety of brightly colored red, yellow, and orange fruits and vegetables.
2.) Limit alcohol consumption.
Based on extensive reviews of research studies, there is a strong scientific consensus of an association between alcohol drinking and several types of cancer.(6) Important to note is that the risk of developing cancer increases with the amount of alcohol a person drinks, with the research indicating that a prudent approach with alcohol is to limit consumption to 1 drink/day for women or 2 drinks/day for men.(3)
3.) Avoidance of charred or burnt meat.
Cooking meat, specifically muscle meat, at high temperatures can result in the formation of chemical compounds called heterocyclic amines (HCAs). Clinical trials have shown that exposure to HCAs can cause cancer in mouse models.(7) Researchers have used comprehensive surveys in numerous epidemiologic studies to estimate the consumption of HCAs in the diet of study participants, and found that high consumption of well-done, fried, or barbecued meats was associated with increased risks of colorectal(8), pancreatic(9,10), and prostate(11,12) cancer.(13) To avoid the formation of HCAs in dishes that contain meat, opt for low-cooking methods such as using slow-cookers and baking.
4.) Dietary fiber intake.
Total fiber intake is not associated with reduced cancer risk among all cancer types; however, the risk of colorectal and liver cancer is inversely (i.e. opposite) associated with the intake of total dietary fiber.(14) Research from the European Prospective Investigation into Cancer and Nutrition (EPIC) found a lower colorectal cancer risk per 10 g/day increase in total fiber intake.(14) General dietary recommendations for total fiber are 14 grams per 1,000 calories; in practice that would equate to roughly 28 grams of fiber in a 2,000 calorie daily diet. As with vegetable and fruit intake, these numbers can be achieved through the inclusion of fiber-rich foods in the diet. For example, there are 11 grams of fiber in approximately a half-cup of navy beans, and nearly 13 grams of fiber in a half cup of almonds.
5.) Specific dietary components with anticancer activities.
As we’ve discussed, mutations and genetic changes are at the root of eventual cancer development. The role of plant-based foods, alcohol, meats, and fiber may involve protection against such genetic damage, but their specific mechanisms of action have been difficult to elucidate. In contrast, there is a good deal of research examining the biochemical properties of specific nutrients that act as epigenetic-regulating agents against cancer. Epigenetics is concerned with the modification of gene expression rather than alteration of the genetic code itself. Recall that cancer often results from mutations caused by repeated environmental incidents that serve to damage DNA and influence gene expression. The following compounds have support for their cancer-protective properties:
While the studies vary on the amounts and forms of these specific dietary components and their direct role in reduction of cancer incidence, it remains clear that each has direct biological activity on the cellular alterations associated with tumor development and cancer progression. From a nutritional perspective, incorporating EGCG and curcumin in either their natural forms of green tea and turmeric, or in a high-quality supplement may provide some degree of support when in the context of a healthy diet as outlined above.
6.) Dietary restriction.
A great deal of interest has surrounded methods of dietary restriction in longevity and disease prevention. Restricting dietary intake in one form or another should be performed with caution and under the direct supervision of a qualified health professional. The three primary forms of dietary restriction that have been studied most extensively include caloric restriction, ketogenic diet, and intermittent fasting.
This examination of dietary restriction models looked specifically at the effects in animals and not humans, so while the results are promising, more clinical trials with human participants need to be conducted.
In summary, we can say with confidence that DNA is not destiny, and that we have a good degree of control over our risk for cancer by what we choose to put on our plates each day. Following the guidelines outlined above and incorporating some specific dietary components provide us with practical tools to manage our health and ease our fears against the threat of cancer in our lives.
There is certainly much more we could discuss regarding the role of nutrition in cancer prevention. What questions do you have? Have you heard about a certain diet or nutrient that supposedly protects against cancer and are curious about its credibility? Want to find out if the claims are supported by science? Comment below and let’s continue the discussion!
About the Author: Jason Bosley-Smith, MS, LDN, CNS, FDN
Jason is a 15 year veteran in the health and wellness field. He has a Master of Science in Nutrition and Integrative health and is a Licensed Dietetic Nutritionist, a Certified Nutrition Specialist, and is Certified in Functional Diagnostic Nutrition. Additionally, he is a Certified Strength and Conditioning Specialist and a Certified Lifestyle Coach. He is a faculty member at the Maryland University of Integrative Health, a guest lecturer a George Washington University and at the Institute for Integrative Health, and a nutritionist with the Center for Integrative Medicine at the University of Maryland School of Medicine. Read his full bio here. To schedule an appointment with Jason, call 410-448-6361.
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