This past week, one of the prime news stories on virtually every major news outlet, aside from the usual accidents, deaths, and robberies, has been the recent announcement by the World Health Organization (WHO) that red and processed meats are directly linked to the risk for colon cancer development. [1] Included in these dietary choices is bacon, sausage, smoked meats, balogna, salami, and basically everything else that appears to be processed. The big question that I am already being asked as a cancer doctor is, “if I eat bacon or hot dogs or anything like that, am I going to develop colon cancer?” My answer is absolutely not. Now, I will attest that there is data to support these claims by the WHO, but I think completely rejecting these types of foods is not necessarily the answer, as there is a lot more to cancer development than what particular type of food you eat.
Colorectal cancer is a very common cancer in the Western World (meaning us here in North America) and despite advances in surgery, chemotherapy and screening, it is still the second leading cause of cancer deaths in this part of the world.[2] It has long been shown that there are major geographical variations in the frequency of colorectal cancer in different parts of the world, with a significantly higher risk in affluent countries such as the US. Previous clinical studies have linked dietary habits and lifestyle factors as the primary explanation for these differences. The main observation that prompts this conclusion is that there are many more colorectal cancers in the US than say in China or Japan. Then, simply consider some of the differences between these 2 countries in terms of lifestyle – diet choices, frequency of obesity, and exercise obviously stand out. There have also been cohort studies (a study where you follow a group of people for a period of time and make observations) where Japanese immigrants to the US were studied for beginning in the 60s, and over time with the adoption of the Western Diet – their colorectal cancer rates rose from the relatively low numbers of Japan to the higher numbers seen here in the US.[3]
The Western Diet, also called Western dietary pattern or the meat-sweet diet, is a dietary habit chosen by many people in some developed countries, and increasingly in developing countries. It is characterized by high intakes of red meat, sugary desserts, high-fat foods, and refined grains.[4] I got this one straight out of Wikipedia! Think about the Western Diet as all of those foods we would like to eat if there were no consequences. Consisting mostly of the non-essentials.
It is a well understood mechanism that local inflammation within the intestines creates the environment that helps the development of a cancer.[5] That being said, the specifics behind what kind of inflammation, how much, for how long, what specifically causes it, and in which people is very poorly understood. Scientists turn to animal models (mainly in mice) and epidemiology studies to better understand this influence. In mice, studies have been conducted where they will feed mice only red meat for example, and then compare the intestinal mucosa with mice who eat regular diets of grains. These show more local inflammation in the meat-only diets. We cannot obviously replicate these studies in humans – as we’re never going to require a person to eat only red meat for 6 weeks, and then sacrifice them in order to evaluate their entire GI tract. No one would sign up! Epidemiological studies, on the other hand, are often very different – they typically consist of surveys asking people about their behaviors such as how much and of what foods they consume – then cross compare that with cancer rates. The result is lofty conclusions that change from year to year. Just like how 2 years ago, moderate consumption of alcohol reduced the risk for colorectal cancer, and this year, moderate consumption alcohol may actually cause colorectal cancer. Confusing, and then what exactly is moderate? As far as diet and lifestyle, there are a few notable items that are most likely contributing factors: [Disclaimer – this list is not meant to be comprehensive or extremely detailed…I am hitting what I view to be the high points.]
Red Meat There have been several epidemiological studies suggesting red meat to be linked to colorectal cancer. Composite comparisons suggest that consumption of more than 30g per day of red meat can raise the risk for colorectal cancer by 10%,
How much is 20 grams of meat?
And a SEER study in 2007 suggested that consuming more than 100g per day of red meat can raise the risk as much as 37%.[6-9] Those are big numbers. The recent WHO announcement says 50g per day increases your risk 18%! [1] Considering the average person has a 5% risk for developing colorectal cancer in their lifetime, a 10% increase means your risk just went up to 5.5% (that’s half a percent up from 5%), and a 37% increase means it becomes 6.85%. The WHO risk increase = 5.9%. Those are not that big anymore. The mechanism of how red and processed meats exert their detrimental effects relates to the amounts of undigested protein that undergoes degradation from normal gut bacteria and fermentation occurs which produces local inflammation and the generation of free radicals and nitric oxide compounds which can foster the types of mutations that can lead to a cancer. This is well understood. In addition, the type of cooking such as baking versus grilling can produce different effects such as those tasty charred lines on a steak that seems to enhance flavor, they do contain substances that are known carcinogens. What is not known is how much and if those carcinogens that we have identified in labs can truly exert their effects in the tiny crypts of the intestines and at what concentrations.
Fiber Diets high in dietary fiber, defined as 25-30g per day have been linked to reduced colorectal cancer rates. [10] So much so that, it is possible that fiber can counteract some of the negative effects of red meat. Fiber works by increasing the bulk of stool by stimulating gut flora, speeding up transit times, and as a result, there is less time for these potential carcinogens to be active. What is fiber and where do we get it? Cereals (not fruit loops – cheerios, shredded wheat, etc.), breads, whole grains, vegetables, etc.
Fibre-rich foods. All these foods are high in insoluble fibre, the portion of plant foods that cannot be digested by the body. Insoluble fibre absorbs water, thereby helping the passage of other foods and waste products through the gut.
Tobacco Guess what. More than any other dietary or lifestyle choice, smoking tobacco beats them all. Tobacco smoking not only increases the risk of cancer in the lungs, but also in organs such as the kidney, bladder, cervix, lower urinary tract, pancreas and the colon and rectum. There is a linear increase in the risk of CRC with smoking consumption, which is considered to be responsible for 12% of all colorectal cancer cases. [11] Simply smoking cigarettes for 10 years raises your risk for colorectal cancer alone by 25%. [12] That’s worse than red meat…
No question here… Smoking Kills!
Alcohol Alcohol comsumption is responsible for 6% of all deaths in the western world and is a significant risk factor for many cancers.[13] Approximately 10% of all cancers in men and 3% of cancers in women are considered to be attributable to alcohol use. [14] Daily alcohol consumption has been suggested to increase the risk of CRC, where 10 g/d increases the risk by 10% and 100 g/wk increases the risk by 18%. [15] Similar to suggested reasons red meat is harmful, as alcohol is broken down and digested, the primary metabolite acetaldehyde is a damaging substance that increases local inflammation, hence explaining its causative effects.
The big picture with each of the above items is that, aside from Tobacco, there are just about as many studies that suggest these items are good as they are bad. There are no studies that suggests Tobacco is good for anything other than Parkinson’s Disease – and we have better drugs for that anyways. The consensus opinions are what I have posted above, meaning there are slightly more studies in favor one way or the other, and this is the reason that all of the recent news reports say red meat is “probably” linked with colorectal cancer, rather than anything more conclusive.
Cancer is such a complex process that there is no single one factor that determines it. To paraphrase a famous radiation biologist named Judah Folkman, “to think that there is one pathway that we can block with a drug and cure cancer is like thinking you can prevent a person in a single car from driving from one end of New York City to the other by blocking only a single intersection.” The key being that there is a limitless and intertwined combination of possible roads, walkways, and pathways that lead to a cancer. There are obviously superhighways, such as inheriting a cancer gene, but in this analogy, red meat amounts to being a 4-lane road instead of a 2-lane – probably going to be a contributor, but its definitely not the main or only means of getting there. The more important conclusion from the above statements is that under the right conditions, there are many dietary food items and lifestyle choices that can enable the development of a cancer.
As mentioned above, epidemiological studies tend to focus on frequencies – how many people admit to eating a certain amount of red meat per day – then we cross that with how many develop a cancer. Many of the dietary concerns that appear to be linked with a cancer are more or less a pattern that has been seen among patients with cancer. In my opinion, the bigger issue than simply the presence or absence of processed foods in the diet is how these tie in with overall health. The concept of the western diet is intimately linked with obesity. If you simply look at questionnaires, and poll 2 different people: one who admits to eating a well rounded diet consisting of the recommended amounts of vegetables, fruits, fiber, meat, fish, and dairy each day and compare that to one who does not eat fruits or vegetables, but instead drinks alcohol daily, and lives on predominantly high fat, high calorie foods – it will be easy to tease out who has better overall health. Now picture which one will be obese – you can predict that one. Now also picture which one exercises regularly. Obesity, or more aptly having a higher concentration of adipose tissue, is directly associated with higher circulating levels of estrogens, leptin, and pro inflammatory cytokines – all of which are associated with the development of cancers. That is not epidemiological data – that is proven scientific fact. The Western Diet is what causes our so called obesity epidemic, and on the horizon currently is new information supporting that another key pathway in cancer development is that of insulin resistance and elevated cortisol levels, the same that results from the metabolic syndrome – a condition synonymous with obesity.
My take on the entire dietary recommendations is that all foods are essentially fine when taken in moderation, although [quote align=”center” color=”#COLOR_CODE”]Every Body can stand to clean up their diet and get rid of some junk.[/quote]
Are you going to develop colorectal cancer because you ate bacon with breakfast – NO! Are you going to develop colorectal cancer because you eat 3 strips of bacon every day for breakfast – Probably not, but your risk is going to be slightly higher than the person who eats a scrambled eggs with toast and fruit every morning. I personally happen to enjoy red meat from time to time, and when I finish an Ironman – there is bacon in my very near future, but it is not my day to day protein source as it should not be for anyone. Rather than particularly single out any one food item, we should be looking at the entire diet package and try to eat right.
It all comes down to making good decisions…
References: 1. World Health Organzation. http://who.gov. Accessed 10/27/15. 2. American Cancer Society. http://cancer.gov. “Important Cancer Statistics – Colorectal Cancer.” Accessed 10/26/15. 3. Tamakoshi A, Ozasa K, Fujino Y, Suzuki K, Sakata K, Mori M, et al. Cohort profile of the Japan Collaborative Cohort Study at final follow-up. J Epidemiol. 2013;23:227–323. 4. Western Diet. http://wikipedia.com. Accessed 10/26/15. 5. Terzić J, Grivennikov S, Karin E, Karin M. Inflammation and colon cancer. Gastroenterology. 2010;138:2101-2114. 6. Alexander DD, Miller AJ, Cushing CA, Lowe KA. Processed meat and colorectal cancer: a quantitative review of prospective epidemiologic studies. Eur J Cancer Prev. 2010;19:328-341. 7. Alexander DD, Weed DL, Cushing CA, Lowe KA. Meta-analysis of prospective studies of red meat consumption and colorectal cancer. Eur J Cancer Prev. 2011;20:293-307.[PubMed] [DOI] 8. Cross AJ, Ferrucci LM, Risch A, Graubard BI, Ward MH, Park Y, Hollenbeck AR, Schatzkin A, Sinha R. A large prospective study of meat consumption and colorectal cancer risk: an investigation of potential mechanisms underlying this association. Cancer Res. 2010;70:2406-2414.[PubMed] [DOI]5. 9. Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective 2007. Available from: http://www.dietandcancerreport.org/cancer_resource_center/downloads/Second_Expert_Report_full.pdf. 10.Aune D, Chan DS, Lau R, Vieira R, Greenwood DC, Kampman E, Norat T. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2011;343:d6617. 11.Botteri E, Iodice S, Bagnardi V, Raimondi S, Lowenfels AB, Maisonneuve P. Smoking and colorectal cancer: a meta-analysis. JAMA. 2008;300:2765-2778. 12.Jensen K, Afroze S, Munshi MK, Guerrier M, Glaser SS. Mechanisms for nicotine in the development and progression of gastrointestinal cancers. Transl Gastrointest Cancer. 2012;1:81-87.[PubMed] [DOI] 13. Schütze M, Boeing H, Pischon T, Rehm J, Kehoe T, Gmel G, Olsen A, Tjønneland AM, Dahm CC, Overvad K. Alcohol attributable burden of incidence of cancer in eight European countries based on results from prospective cohort study. BMJ. 2011;342:d1584.[PubMed] [DOI] 14. Moskal A, Norat T, Ferrari P, Riboli E. Alcohol intake and colorectal cancer risk: a dose-response meta-analysis of published cohort studies. Int J Cancer. 2007;120:664-671.[PubMed] [DOI] 15. Cho E, Smith-Warner SA, Ritz J, van den Brandt PA, Colditz GA, Folsom AR, Freudenheim JL, Giovannucci E, Goldbohm RA, Graham S. Alcohol intake and colorectal cancer: a pooled analysis of 8 cohort studies. Ann Intern Med. 2004;140:603-613