I am not a vegetarian, but…
Quite recently I have been watching many YouTube videos about various dietary approaches, reading the blogs and discussions and contributing to some. What I have noticed was a constant duel between two opposites: while some people have adopted (some of them exclusively) a plant based lifestyle, finding better health and personal satisfaction with their choice, the meat eaters and Paleo advocates also celebrate improved insulin resistance, plasma cholesterol or significant weight loss with the low-carbohydrate approach. I have found vegans very enthustiastic about their choice showing a tendency to encourage others going vegan, whereas few individuals from the meat eating group attacked me and called me a vegan troll when I did not agree with their mainly meat based diet. For many the ‘Protein’ has become a new savior because it tastes great (especially of animal origin) and it has a high satiety effect promoting a weight loss. These two attributes are making a high protein diet very attractive in the modern era of the obesity pandemics. Moreover, since the saturated fat has been partly cleared of the cardiovascular diseases stigma (see Dr Alseem Malhotra), the meat eaters did not need more. Now we have Dr Greger, a vegan, on one side and Gary Taubes, a low-carbohydrate, high protein and high fat intake advocate, on the other side. Each of them present some pieces of evidence supporting their claims and attracting thousands of followers worldwide. Pieces of evidence, I say, because this is important. As a nutritionist who is standing on a neutral land and having an interest in the objective truth about how to stay healthy without going to extremes, I see the weaknesses in their arguments, in the choice of these arguments and, more importantly, the interpretation of the evidence.
I am not going to discuss each of these dietary practices to the detail here. Instead, I would like to bring to your attention some information that made me to write this article. It is not a new information to me but a repeated exposure to this information recently prompted me to share my views. By writing this article I intend to highlight that although I consider myself an omnivore and I appreciate the nutritional value of the animal products, I do recognize the benefits of the primarily plant based diet with the animal sources forming the minority.
The information, which made me to write this article, were the World Cancer Research Fund (WCRF) dietary recommendations for the colorectal (bowel) cancer prevention. On the WCRF website there is a statement: “In November 2007, World Cancer Research Fund global network published its landmark Expert Report (WCRF, 2007), which was the most comprehensive report ever produced on the links between lifestyle and cancer risk.” The lifestyle also includes the diet. They further announced that creating this report took 6 years and they looked into around 7000 relevant quality studies (out of over a million, initially narrowed to 22 000, quite impressive, is it not?). All these materials covered all sorts of cancer, but I am going to focus on the colorectal cancer in this article. After evaluating a total of 30 cohort studies and 115 case-control studies, the WCRF came to conclusion in their Report that:
“A substantial amount of data from cohort and case-control studies showed a dose-response relationship, supported by evidence for plausible mechanisms operating in humans. Red meat is a convincing cause of colorectal cancer.”
“There is a substantial amount of evidence, with a dose-response relationship apparent from cohort studies. There is strong evidence for plausible mechanisms operating in humans. Processed meat is a convincing cause of colorectal cancer.”
Since browsing the WCRF website I have checked other sources listing the risk factors of the colorectal cancer, such as Cancer Research UK or European Prospective Investigation Into Cancer and Nutrition (EPIC). They basically keep saying the same with small differences: that red meat, and particularly processed meat, was associated with the colorectal cancer. Some studies found this link with white meat, while others did not and the same was for the strength or weakness of the link related to fish, or no link at all. It really depends on the design of the study and it is nothing unusual that studies examining virtually the same thing do not always come to the same conclusion.
Of course, most of the ‘evidence’ was primarily based on the observational (case-control and cohort) studies, which are not able to provide a true evidence of the cause-effect relationship. This uncertainty is a result of many inborn factors of such study designs, including the misreporting of food (items) consumption in the questionnaires or a whole range of confounder factors in the diet composition, physiological state of the participants (ethnicity, age, illnesses, culture) or a lifestyle in general (physical activity, socio-economic status, living in a city or urban area, smoking, etc.). There is also a see-saw effect present: people consuming higher amount of meat tend to consume less fruits and vegetables, smoke more and exercise less, which also have some impact on the overall cancer risk. However, while we do not have better data, we have to use what is available and interpret it accordingly. This means that when an association was found this should not be mistaken for a cause-effect relationship. However, ignoring this observation as not supported by the experimental evidence, which is problematic in humans in relation to cancer, is not good also. Limitations of the findings tend to be listed and discussed in the individual reports so that the reader is made aware about the applicability of the information. Other studies were performed on human tissues or on animals in vivo, examining the mechanisms of the cancer development after various dietary exposures on the molecular level.
In 2011 the WCRF had published an update after examining dozens of additional studies: Colorectal Cancer 2011 Report (see the reference), where they confirmed their conclusions from the 2007 Report, stating that the evidence about effect of the red and processed meat on the cancer has strengthened. After all, probably the most complex overview of the up to date evidence about the cancer published in the WCRF suggests that both of these meat items (red and processed) in excess represent a risk to human health.
What is it about the bowel cancer?
Before I start the main discussion and provide the arguments, I would like to explain, why I have decided to bring this factor into the vegan vs. carnivore disputes. The colorectal cancer death rate in the UK is the third most common form of cancer, according to the newest figures of the Office for National Statistics (2013) and the same is the case worldwide. One of the reasons for the bowel cancer development is that the intestine lining tissue is metabolically very active and it is being replaced at a very high rate: within a few days each of us have a new bowel lining. This is good for healing, but with such a high turnover rate of the tissue, when there is a frequent transcription and multiplication of the DNA, this provides more opportunities for an error during the DNA replication. Therefore, anything that promotes the changes in DNA can contribute to the formation of a tumor. In most cases these replication mean nothing. We produce damaged DNA all the time and our immune system and other cellular corrective mechanisms can deal with it without any major consequences. However, in some cases, when more of these errors accumulate on specific DNA regions and such damage has not been noticed by the corrective mechanisms inside of our body, it can result in the cancer. The problem with the cancer is that it does not usually hurt during the time when the cure would be the most efficient. Even when people experience some discomfort in their private area, they hesitate to rise their concerns to the doctor until it is too late. This only adds to the death rate due to the late diagnosis despite the colorectal cancer is one of the easiest to treat when discovered early.
Since the prevention is better than cure, in order to reduce the risk of colorectal cancer, the WCRF recommends to limit the consumption of red meat (beef, lamb, pork, goat) to the maximum of 500 grams of cooked weight per week, and, if possible, to completely avoid processed meat, such as sausages, smoked bacon, salami and others. This recommendation was based on the evidence that the bowel cancer was more frequent among people who consumed large amounts of these meats and meat products. Those 500g are only an approximate number which does not distinguish between the healthy limit for men and women separately. Nonetheless, the association between the consumption of other kinds of meat was less convincing (poultry or even the fish) than of the red and processed meat. Why is that?
Well, one of the reasons for cutting down on red meat is that it is rich in the haem molecule, the one responsible for the red color of the meat (myoglobin). This haem molecule is similar to the one we have in our red blood cells (remember the haemoglobin?) and which is essential for binding oxygen that needs to be delivered to the most distant cells in our body otherwise they would die. This haem compound in meat has been found to ‘damage the lining of the colon‘, according to WCRF, based on the experimental studies in the laboratories. The mechanism was suggested as working in two ways. Firstly, the haem iron is more bioavailable, i.e. easily accessible to the body and the free iron, which is released at the site of the intestinal lining for the absorption, can contribute to the oxidative stress and damage of the DNA. Another reason are the ‘suspected mutagenic and carcinogenic’ N-nitroso compounds. Not only the haem molecules promote their formation, but the added nitrates in the processing and preserving of the meat products (bacon, sausages, salami) contribute to the pool of the produced N-nitroso molecules, too.
These nitrates, which are then naturally converted to nitrites, are added for three main reasons: 1. the visual properties of the products (they keep the meat fresh looking and attractive), hence contributing to the profit of the manufacturer, 2. they add a rich meaty flavor to the product, making it palatable and 3. to inhibit growth of the bacteria responsible for the food poisoning, including the botulism, hence protecting the public from the acute disease.
Furthermore, the high heat applied to meat causes the formation of polycyclic aromatic hydrocarbons and heterocyclic amines, which are the reason why we so much love barbecue and the browned crust on the meat or the chicken skin. These compounds give the characteristic flavor to the meat prepared this way, but they were also found to be carcinogenic, regardless of the kind of the meat (red or not), and people are advised to eat them only sporadically or avoid them completely.
Based on this knowledge it is obvious that people who consume a lot of red and processed meat should reduce its consumption if they want to cut down the risk of developing a bowel cancer.
Although I have encountered some articles saying that other organisations, such as National Research Council or the American Cancer Society (see Danilo Alfaro, n.d. or Matt, 2010), have not confirmed the link between the nitrates and cancer, these articles were written for the culinary purposes, hence favoring the flavor above the health risks. I have contacted these two organisations for more information regarding what would be their comment on that their claimed statements is in contrast with another big attempt of WCRF to summarize the overall evidence. The American Cancer Society replied to me the very next day via Facebook, confirming the findings of WCRF regarding the colorectal cancer and red and processed meat products, hence contradicting the claims presented in the article of Danilo Alfaro.
In contrast to the potentially damaging effect of high amounts of consumed meat, I have learned (from the evidence based sources, including the WCRF report) that the consumption of resistant starch and other complex carbohydrates promote the anti-cancer environment in the large intestine. This is achieved by the intestinal bacteria and other microorganisms, which digest (ferment) these carbohydrates, forming other beneficial substances such as butyrate. This compound was found to serve as a fuel for the intestinal cells, regulating their growth and stimulating their apoptosis (the programmed cell death). This is pretty much in opposite to the cancerous uncontrolled growth, is it not? The body is normally very clever in maintaining the health of its tissues. Complex carbohydrates also come with the soluble and insoluble fiber, increasing the bulk of the stool and reducing the transit time. One will go on the loo more often than once in two days as it often happens with the constipation, but this significantly reduces the contact time between the toxins and the intestinal lining, decreasing the chances for damaging the DNA and finally the risk of the colon cancer.
How far to go in the dietary changes
After reading about the recommended limit of 500g of red meat per week I became curious to find out what the current consumption of red meat was in the UK. I have visited the website of the National Diet and Nutrition Survey UK (NDNS) and found the data tables from the combined years 2008/9 and 2009/10. I have selected the relevant information and looked at the figures. Are you interested in what I have found? Keep reading.
From the diagram on your right, which I have plotted from the selected data of the NDNS mentioned above, it appears that the poultry is the most consumed meat in the UK. However, when adding all red and processed meat products together and excluding the poultry (I had no control over the poultry part in the processed meat and other meat products), the men consumed on average 2037g per week, which was over 300% more than recommended 500g, and women consumed average 1330g per week, exceeding the recommendations by over 100%. In comparison, the poultry meat consumption among adult men and women was 798g and 658g per week, respectively. These data are the average for the general population, representing a reference man/woman, consuming all these in one week. This is the British population reality. The dairy, fish, condiments, pastry (except of the meat pastry), sugary items, beverages and others were not included due to a little relevance to this article. So, if the figures I have presented here are correct, it will be a tough job to reduce the red and processed meat consumption to the relatively safe amounts stated by the WCRF. This is particularly true when you imagine that the mean values are not the real values of every citizen. Instead, the mean values include people consuming little or no meat at all and others consuming far more than the average amounts presented here. In fact, when I was examining the data, the standard deviation, a measure of how the consumption varied from the mean values, was even three times higher than the mean values for some variables. And this is alarming because people who consume substantially more of the risky meat are those having the highest risk of the colon cancer. Moreover, people who tend to consume processed meat on regular basis tend to be those who consume the least of the complex carbohydrates (and other protective plant compounds within), which only adds to their chance of developing bowel cancer sooner or later.
What the low-carbers have missed
Here I am finally coming to the main reason for writing this article. Probably all advocates of low-carbohydrate diet focus on the short-term effect of the animal rich diet such as improved lipid profile, insulin sensitivity, gradual decreasing adipose tissue, and the ability of this diet to keep these metabolic variables under control. The changes of these variables were noticed within two weeks, according to Dr Kimber L Stanhope, whose name appears in many studies examining the effect of fructose/sugar on human metabolic health and who has also appeared in several TV shows dedicated to this topic. In contrast, nobody seems to be interested in a long-term effect of such diet on cancer.
Gary Taubes specifically praised Dr Atkins for his dietary recommendations and pronounced such diet as healthy for its benefits mentioned above. The healthiness was emphasized in contrast to the past belief about the saturated fat being the main factor in the cardiovascular diseases development. In one of his blogs (Taubes, 2011), Gary recommended animal based diet for most people and other plant foods rich in proteins for vegetarians to cure or even avoid weight gain or obesity. I agree with the vegetarian part but not with the dominance of animal products rich in dairy, eggs, fat and meat of all kind as Dr Atkins used to promote and his followers are readily adopting. In such diet the plant sources are the minority, hence there is a little variability in the diet, having a narrowed list of some vegetables (mainly non-starch vegetables) and less sweet fruits. This leaves out the whole spectrum of other healthy plant foods, regardless of the level of processing applied onto them. While low processing is good, the highly processed and nutrients depleted modern food industry products provide little nutrients but plenty of energy and sometimes a cocktail of additives, which we all want to reduce. Less plant food in the diet provides less fiber and other secondary compounds such as resveratrol, anthocyanins and others, being under research for their anti-ageing, anti-cancer and many other anti-disease properties. And there is another component in such foods which is lacking in the low-carbohydrate diet: it is the resistant starch discussed earlier. It can be found in starchy and relatively carbohydrate rich plant sources (pulses, grains or even not overly ripen bananas). These are exactly the ones that the low-carb advocates want to avoid. However, I hope that the following summary will make you clear why I am criticizing this dietary approach, when applied for a long period of time:
The WCRF had clearly stated that there is a convincing evidence about the health risks of red meat consumption, whereas the evidence of benefits of various non-starch vegetables for colorectal cancer are rather limited, based on the inconsistent evidence. Therefore, if one is risking health with high consumption of processed meat, the little amount of non-starchy vegetables might not provide a protection from the potential harm. However, the starchy plants (rich in various forms of fiber) have been found to help preventing the colorectal cancer (the butyrate discussed earlier). More specifically: there was an apparent clear dose-response relationship between the fiber intake and the colorectal cancer epidemiology. This conclusion was based on a consistent evidence of the examined studies, which were of the observational but also the experimental nature.
In short: while the meat consumption may be harmful and the allowed plant foods provide little protection (if any at all), the starchy vegetables evidently providing the protection against the colorectal cancer are excluded in the low-carb diet. Do you see the connection?
In the current British (westernized) diet the plant sources are dominating while Britons already consume high amounts of potentially hazardous animal products. What could we expect if this ratio had flipped over and the plant food have formed the minority while the animal food would supply most of the energy and proteins? I suggest that in this era of the food industry domination, the consumption of unprocessed or little processed plant foods would be very low and the processed carbohydrates would still have found their way to the diet of a westernized man or woman. And nobody would complain about being encouraged to eat more meat, eggs, sausages or fatty cheese, because they taste so bloody good! The majority of the population is hooked on the palatability of the processed food, and they will keep going to the fast-food outlets even if you have stood at the door and told to each one of them that they were speeding up to their graves. The taste factor is so strong here that it overrides the sense for self-preservation. For many the short-term pleasure is evidently more attractive than the long-term health benefits.
The proof that Gary Taubes have omitted the long-term health risks of high animal products consumption is his article (Taubes, 2012), where he produced an impressive critique of the Pan et al. (2012) analysis. This analysis reported the results of the two large cohort studies, examining the association between the consumption of red meat and the total, cardiovascular and cancer mortality. Gary wrote:
“So we do a randomized-controlled trial. Take as many people as we can afford, randomize them into two groups — one that eats a lot of red meat and bacon, one that eats a lot of vegetables and whole grains and pulses-and very little red meat and bacon — and see what happens. These experiments have effectively been done. They’re the trials that compare Atkins-like diets to other more conventional weight loss diets — AHA Step 1 diets, Mediterranean diets, Zone diets, Ornish diets, etc. These conventional weight loss diets tend to restrict meat consumption to different extents because they restrict fat and/or saturated fat consumption and meat has a lot of fat and saturated fat in it. Ornish’s diet is the extreme example. And when these experiments have been done, the meat-rich, bacon-rich Atkins diet almost invariably comes out ahead, not just in weight loss but also in heart disease and diabetes risk factors. I discuss this in detail in chapter 18 of Why We Get Fat, ”The Nature of a Healthy Diet.” The “Stanford A TO Z Study” is a good example of these experiments. Over the course of the experiment — two years in this case — the subjects randomized to the Atkins-like meat- and bacon-heavy diet were healthier. That’s what we want to know.“
I do not know how Gary, but I want to know the whole story, the whole picture, not only a part of it. High body and abdominal adiposity have also been associated with various forms of cancers, including the bowel cancer. This constantly has been excluded in the argumentation of Gary and others advocating this high meat – high fat dietary approach. I have highlighted the details which were the most relevant to this article:
- Performing randomized-controlled trial on humans when studying the cancer development is difficult for ethical reasons. Instead we have mainly the observational studies, even with their limitations, and laboratory studies on animals or isolated human tissues, which are also not too representative of the whole human body in its complexity.
- There was mentioned weight loss, heart disease and diabetes risk factors. Nothing about cancer.
- A third point of mine: the “Stanford A TO Z Study” and the conclusion of being healthy. In what sense? There were examined the effects of various dietary approaches on the body weight, blood pressure, insulin and blood glucose levels and also the blood lipids. Nothing about cancer. While I agree that the diet that helps to reduce body fatness can contribute to reduction in various forms of cancer, the bowel cancer seems to be rather exception here, when this most effective Atkins and similar diets virtually increase the risk of bowel cancer, while reducing the overall body adiposity. In addition – little or no attention has been paid to the physical activity, which also helps to improve all discussed risk factors, including the cancer.
- Finally: the TWO years covered by the Stanford A to Z study is quite a short period of time to study the development of cancer on the human population, is it not? In fact, the abstract of this particular study ended with: “While questions remain about the long-term effects and mechanisms, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.”
This only confirms what I have highlighted earlier: a short-term focus on metabolic health, omitting the potential long-term effect in relation to cancer (and perhaps other diseases).
It was a lengthy and exhaustive article of Gary which heavily analyzed and criticized a single analysis of Pan et al. (2012). This analysis concluded: “Red meat consumption is associated with an increased risk of total, CVD, and cancer mortality. Substitution of other healthy protein sources for red meat is associated with a lower mortality risk.” I understand that the Gary`s article was a response to the demand of his readers who pointed out the media coverage of this study that time (2012), but still, the cancer part was ignored completely and only the metabolic consequences of the Atkins and similar animal based diets were highlighted as the proof of their healthiness. While I appreciate Gary’s knowledge and his hard work in raising awareness in the weaknesses of such (observational) studies, I want to know more about the long-term effect on human health when following his dietary recommendations, not only what he wants to know and what his overall work suggests.
Is it only about the insulin?
While the low-carbohydrate diet might appear healthy in a short time by improving the metabolic variables discussed earlier, the long-term effect of such diet was excluded during its promotion. Instead, Gary and others sometimes highlight the role of insulin in the cancer development as a consequence of the consumption of high glycaemic carbohydrates. By this logic the lower insulin excretion should protect against cancer – giving another tick to the list of beneficial effects of this diet, especially when we are talking about the processed, not the complex carbohydrates and the soluble fiber. I am OK with that, if it only was the whole story. It is true that cancer is tightly linked with the insulin, but there is another factor associated with cancer: insulin-like growth factor (IGF-1). The function of these molecules is interlinked and they are also structurally similar which is why they share some of our receptors. However, while insulin is increased with the processed carbohydrate-rich diet, it is the protein intake that increases IGF-1 more than carbohydrates, according to Kaklamani et al. (1999). Another study of Giovanucci et al. (2003) have found association of increased IGF-1 in men after higher consumption of ALL proteins, including the total plant proteins, but not of the red meat (surprise?). High fat intake and positive energy balance were also associated with the IGF-1. Although the incidence of cancer with high protein intake was not reported in this study, the IGF-1 was positively correlated in various cancers, including the colorectal, in younger and older males in another study back in 1999: Ma et al. (1999).
Overall, the high protein intake and also the high animal protein intake has generally been associated with the increased risk of various forms of cancers in a number of studies. Therefore the long-term effect of the high protein and high fat diet seems to favor the increased risk of cancer development and it should not be promoted as a healthy diet in a long term.
And this is where I would like to end this rather lengthy article of mine. One thing I would like to add though: several days ago I came across a podcast, a short interview of Sarah Wilson with Dr Lustig, published on the 3rd April 2014. In that interview Dr Lustig revealed that because he tries to exclude sugar from his diet he likes having eggs and bacon for breakfast, no bread. As you can see, these cancer risks are constantly being ignored even by the health professionals in these times of anti-carbohydrate boom. The public and professionals seem to go from one extreme to another: once so much promoted low-fat and full of added sugar diet has now turned to rather absolutely no sugar but other potentially harmful animal products consumed on a regular basis. My question is: why not replacing the unhealthy bacon with the healthy beans to accompany the eggs, merging the positives of these two food items: controlling the insulin response and providing healthy complex carbohydrates together? I believe it would be much healthier option than having two-three rashers of bacon for breakfast almost every single day.
Update from 21.7.2014: Recently I came across one fantastic article. Although there are some theories and speculations in it, the evidence that the diet rich in natural plant foods promotes health has been widely known for a while, in contrast to diets where these precious treasures of nature are lacking. The article is titled Fruits and vegetables are trying to kill you and contains really interesting information about how sophisticated the nature is and how our adaptation to stimuli can actually makes us stronger and healthier.
Danilo Alfaro (n.d.) Facts about sodium nitrate [Online]. Available at: http://culinaryarts.about.com/od/seasoningflavoring/a/nitrates.htm (Accessed: 14.4.2014)
Giovannucci, E., Pollak, M., Liu, Y., Platz, E.A., Majeed, N., Rimm, E.B., Willett, W.C. (2003) Nutritional Predictors of Insulin-like Growth Factor I and Their Relationships to Cancer in Men. Cancer Epidemiology, Biomarkers and Prevention 12 (2), pp: 84-89
Kaklamani, V.G., Linos, A., Kaklamani, E., Markaki, I., Koumantaki, Y., Mantzoros, C.S. (1999) Dietary Fat and Carbohydrates Are Independently Associated With Circulating Insulin-Like Growth Factor 1 and Insulin-Like Growth Factor–Binding Protein 3 Concentrations in Healthy Adults. Journal of Clinical Oncology 17 (10), pp: 3291-3298
Ma, J.,Pollak, M.N., Giovannucci, E., Chan, J.M., Tao, Y., Hennekens, C.H., Stampfer, M.J. (1999) Prospective Study of Colorectal Cancer Risk in Men and Plasma Levels of Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein-3. Journal of the National Cancer Institute 91 (7), pp: 620-625
Matt (2010) Nitrates and nitrites [Online]. Available at: http://mattikaarts.com/blog/charcuterie/nitrates-and-nitrites/ (Accessed: 14.4.2014)
NDNS (2011) National Diet and Nutrition Survey: Headline results from Years 1 and 2 (combined) of the rolling programme 2008-9 – 2009-10 [Online.] Available at: https://www.gov.uk/government/publications/national-diet-and-nutrition-survey-headline-results-from-years-1-and-2-combined-of-the-rolling-programme-2008-9-2009-10. Accessed 2.4.2014
Office for National Statistics (2013) What are the top causes of death by age and gender? [Online.] Available at: http://www.ons.gov.uk/ons/rel/vsob1/mortality-statistics–deaths-registered-in-england-and-wales–series-dr-/2012/sty-causes-of-death.html (Accessed 4.4.2014)
Pan, A., Sun, Q., Bernstein, A.M., Schulze, M.B., Manson, J.E., Stampfer, M.J., Willett, W.C., Hu, F.B. (2012) Red Meat Consumption and MortalityResults From 2 Prospective Cohort Studies. Archives of Internal Medicine 172(7), pp: 555-563
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Taubes, G. (2012) The science, pseudoscience, nutritional epidemiology, and meat [Online]. Available at: http://garytaubes.com/2012/03/science-pseudoscience-nutritional-epidemiology-and-meat/ (Accessed 13.4.2014)
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