Introduction
What can each of us do to protect ourselves from cancer?
The World Cancer Research Fund (WCRF) is convinced that the answer is "a great deal" - according to the latest research some 30 to 40 percent, approximately a third, of all types of cancer could be prevented by means of healthy nutrition and sufficient exercise. For this reason the WCRF has published eight recommendations which are aimed at preventing the development of cancer.[1, 2]
The recommendations include
1. Keeping body weight within the BMI guidelines (for adults: Body Mass Index of 19 to 25).
2. Undertaking moderate physical activity for at least 30 minutes per day.
3. Reducing consumption of foods with a particularly high energy density (including sugary drinks and fast food) to a minimum.
4. Predominantly eating plant-based foods and replacing highly processed, starchy foods with pulses, wholegrain products and a variety of fruits and vegetables as part of your daily eating habits (ideally, eat 3 to 4 portions of vegetables and 1 to 2 portions of fruit each day).
5. Lowering consumption of meat to a maximum of 500g per week, limiting consumption of red meat and avoiding processed meats (smoked, cured, salted).
6. Limiting alcohol consumption to a maximum of two glasses (men) and one glass (women) per day.
7. Restricting salt intake and avoiding mouldy grains and pulses.
8. Meeting daily nutritional requirements through consumption of "natural" foods, without resorting to food supplements.
These are actually incredibly simple and well-known recommendations which can be easily integrated into daily life with a little determination and effort. You will also find more detailed information on this topic in our nutrition blog post by Professor Nüssler "Eating healthily as well as ethically at the same time - is this really possible?" and on the TZM info portal of the Nutrition and Cancer Work Group (only available in German).
These recommendations seem to be even more important in relation to colorectal cancer than they are for cancer in general. In this connection, there are indications that some 50 percent of all cases of colorectal cancer in the USA could have been avoided through a varied diet, active lifestyle and healthy body weight [1]. Colorectal cancer is one of the most common form of cancers here in Germany. According to the German Cancer Research Centre (DKFZ), approximately one in seven people are affected by this type of cancer. This means colorectal cancer is the third most common type of cancer in Germany after breast cancer and prostate cancer [3]. In the following article we therefore wish to focus on this type of cancer and provide information on how nutrition can act as a means of prevention.
Nutrition in the prevention of colorectal cancer
Colorectal cancer (also known as colon cancer, colon carcinoma and large intestine cancer) is part of a group of cancer types which can be very positively influenced by making changes to lifestyle and nutrition. This has been found in most studies on this topic.
In a large-scale investigation in North America, carried out over several years, it emerged, for example, that people following a vegetarian diet had a 22 percent lower risk of developing colorectal cancer in comparison to the general population. This trend was seen even more clearly in the case of vegetarians who consumed fish (pescatarians). Their risk of developing colorectal cancer was 43 percent lower [4]. Nevertheless it should be considered that vegetarians often tend to have a healthier lifestyle overall, which could also lessen the influence of nutrition.
In addition to vegetarianism there are other forms of nutrition which are known for their health-promoting properties, although findings vary considerably in this area depending on the way the study is designed. For example the preventative effect of a Mediterranean diet, depending on the study, fluctuates between 8 and 54 percent [5]. Further investigations are required in this area.
What would happen if I decide to observe all of the recommendations of the WCRF listed above from now on? A large European study from 2014 provides an answer to this question: men and women between the ages of 12 and 70 years were assisted in making changes to their lifestyle and nutritional habits in a way which lowered their BMI, increased their activity, reduced their alcohol consumption and helped them to eat more healthily. The result - within 12 years the risk of developing cancer in people who improved in all four areas fell by 37 percent. Even those who only improved in three or fewer areas also reduced their risk, albeit to a lesser extent [6].
As is the case for all cancers, the development of colorectal cancer is dependent on many factors. In addition to the factors mentioned here, there are some which we can only influence to a minimal extent or not at all. These include, for example, another disease, special medication, radioactivity, industrial chemicals or simply genetic predisposition. It may, however, be possible to draw an initial conclusion that even minor lifestyle changes can have a positive impact upon health and, as a result, we are able to contribute to lowering our risk of developing cancer.
In addition to the general recommendations, there are also some factors which particularly affect the risk of developing colorectal cancer. Here are a number of examples:
Fibre – a key constituent in colorectal cancer prevention
Plant-based foods provide us with fibre in the diet. Foods which are particularly rich in fibre include, for example, husks of cereal grains, which is why wholegrain products are seen as healthier then products made of white flour. Fruit and vegetables as well as pulses, mushrooms and nuts provide appropriate quantities of this useful substance. In our blog post "Fibre is an essential constituent of our diet" we explore the fact that an intake of 30 g of fibre per day has a positive impact on our health.
The development of colorectal cancer can also be influenced by this - a variety of studies have been able to prove that an increased consumption of high-fibre foodstuffs can reduce the risk of developing colorectal cancer. This effect has been shown to be even more significant for men than for women. In this connection it is also interesting to note that the type of fibre is probably very important. Fibre from grains and pulses seem to have a particularly positive effect [7, 8, 9]. Explanations as to why fibre may have a positive all-round effect include:
- Initially the stool volume is increased through consumption of fibre and therefore the time it takes to pass through the bowel is lowered. This means that the harmful substances from the stool have less time to affect the mucous membrane of the intestines.
- Fibre also acts as a nutrient for our intestinal bacteria. These bacteria use fibre to form fermentation products (short-chain fatty acids) which are beneficial for us in two respects. They provide an acidic bowel environment which inhibits the growth of harmful bacteria and promotes the resorption of important minerals. Furthermore, the short-chain fatty acids support the natural regulation of large intestine cells and their life cycle [8, 10].
Practical tip: Wholegrain products (e.g. wholegrain bread) contain the largest amounts of fibre. The taste of these products can take a while to get used to at first. The switch to using wholegrain flours is often easier - such as very strong or hard/brown flour (type 1050 in Germany). There is almost no noticeable difference in taste to normal soft/patent flour (type 405) but you will increase your intake of fibre. Rye products are also usually made of less finely ground flour and are therefore richer in fibre than wheat products.
Red meat and meat products - how much should I eat? How much is harmful?
"Red meat" generally refers to meat from (domesticated) cows, pigs, sheep and goats. Consumed as part of a healthy diet, a moderate amount of red meat (up to 500g per week) does not constitute a risk of developing colorectal cancer [1, 8, 11]. The recommendation is to consume game, poultry and fish rather than red meat, as the nutritional profile of these types of meats is seen as more favourable than that of domesticated and industrially reared animals. Consumption of white meat (poultry), according to the "Krebsinformationsdienst" (cancer information service of the German Cancer Research Center - DKFZ), has no measurable influence on the risk of developing colorectal cancer [12].
So far, no clear explanation as to why red meat can be cancer causing has been found. One theory focusses on the substance known as "haem", which stimulates the formation of N-nitroso compounds in the bowel of humans. These compounds are said to be potential large intestine carcinogens and are of particular concern when nitrate or nitrite is added to meat to improve shelf life. Red meat is seen to be especially carcinogenic due to haem. White meat contains a much lower concentration of haem. In addition to the formation of N-nitroso compounds, heating red meat at too high a temperature (e.g. when searing) can increase its carcinogenic potential. This can lead to the formation of heterocyclic aromatic amines and polycyclic aromatic hydrocarbons - two compounds which, for people with a genetic predisposition, can lead to colorectal cancer. These compounds do not occur when cooking [8, 10]. Careful and varied preparation, as well as gentle cooking, of food is therefore extremely important.
The data available on processed meat is clearer. Processed meats are those which have been "preserved by means of being smoked, marinated or salted, or through the addition of chemical preservatives". The World Health Organisation (WHO) classified these types of food products as "cancer-causing for humans" in 2015 [13]. Consumption of well-cooked ham or sausage is seen as critical in this connection as it is accompanied by a significant increase in the risk of developing colorectal cancer [14].
Despite all of this, meat is still a very nutritious and valuable part of the diet and most studies have only been able to prove a risk-increasing effect when a certain quantity is exceeded. Consumption of 500g unprocessed meat produced with regard to animal welfare standards per week is perfectly acceptable.
Excess weight and increased abdominal fat as risk factors
Especially in recent years, the connection between a high BMI (> 25 kg/m2) and the risk of developing certain types of cancer has become increasingly clearer. Meanwhile this effect has also been proven for colorectal cancer in a large number of studies. There is a connection between the risk rising by 2 to 4 percent for every "BMI unit" (1 kg/m2). The negative influence therefore increases with increasing excess weight. The effect is twice as pronounced for men as it is for women [6, 8, 15].
A possible explanation for this is that our fatty tissue in the body, and in particular our abdominal fat, is very active metabolically. Fatty tissue produces hormones such as oestrogen and growth factors which influence our bodily processes and can cause mild inflammation. This creates an environment in which tumours can develop and grow more easily. For this reason, in addition to the amount of body fat, the way it is distributed also plays a decisive role in the development of colorectal cancer. If a lot of fatty tissue is stored around the abdomen, the risk of developing colorectal cancer is increased once more [8].
Alcohol – one glass isn't a problem?
There is a proven connection between consumption of alcohol and an increased risk of developing colorectal cancer (10 percent increase per 10 g of alcohol) [8]. The "European Code Against Cancer" of WHO/IARC (International Agency for Research on Cancer) identifies a decrease in the risk of colorectal cancer by up to 31 percent when consumption of alcohol is reduced from more than four glasses a day to a maximum of one glass [16]. Unlike the risk of cardiovascular diseases, there is no dose which could have a protective effect against colorectal cancer. There is a linear correlation - that is, any consumption of alcohol increases the risk of cancer. In particular, people with a low intake of folic acid (contained, for example, in pulses or green leafy vegetables) and/or the amino acid methionine (found in Brazil nuts or salmon, for example) should limit how much alcohol they drink. In this connection, attention should only be paid to the amount of alcohol consumed - irrespective of the type of alcoholic drink. The carcinogenic effect of alcohol is also more pronounced for men than women [8].
But through which mechanism does alcohol increase our risk of colorectal cancer?
In the first instance, it is to do with the reactive metabolites of the alcohol itself, for example acetaldehyde, which can develop carcinogenic effects. A further explanation might be that alcohol can function as a solvent which enables other carcinogens to reach the cells of the intestinal mucosa more easily [8].
The combination of alcohol with smoking tobacco can also increase the risk of cancer. Tobacco facilitates the development of specific mutations in our DNA. Repairing such mutations is hindered by a simultaneous consumption of alcohol [8].
It is open to debate, however, whether people who consume a lot of alcohol generally also eat less well and have a lower intake of essential nutrients, and are therefore more susceptible to developing cancer [8].
Daily exercise
Daily exercise is good for us and is also proven to lower the risk of developing colorectal cancer. Overall we should ensure that we at least comply with the recommendation of taking 30 minutes of moderate physical activity each day. This helps to reduce inflammation in the body, lower the level of insulin and reduce the risk of insulin resistance. On a long-term basis moderate physical activity will also lead to it being possible to reduce body fat, therefore eliminating a further risk factor for many diseases [8].
Garlic, milk and calcium
Garlic
World Cancer Research Fund (WCRF) classifies garlic as "probably protective against colorectal cancer". Studies revealed a slight decrease in the risk through consumption of garlic. Animal studies showed garlic had a protective effect against tumour formation and cell growth. To date, however, there are is no clear evidence that this also applies to humans [8].
Milk
Consumption of milk is also seen to be "probably protective against colorectal cancer". The protective effect fluctuates between a 7 to 9 percent risk reduction depending on the study. It is not clear, however, whether this effect largely originates from calcium (see below).
Calcium
Calcium consumed in the diet is an important mineral for humans. In addition to its importance for the health of bones and muscle strength, it also influences many cellular processes. For example, calcium plays an important role in cell growth, cell division and cell death in normal cells but is also particularly important in the cancer cells of the bowel. Overall, studies confirm a slight protective effect in relation to the development of colorectal cancer through the consumption of calcium.
Conclusion
Everyone can do a great deal to lower their risk of developing colorectal cancer. The fact is that living a "healthy" lifestyle in general is key - also concerning this disease. In a study, for example, it was possible to lessen the negative impact of consuming a large amount of meat and meat products if the study participants increased their consumption of fibre. This effect was also achieved if the amount of fish was increased [11]. Pleasure also plays a central role in living a healthy life. Our Is enjoyment a prerequisite for healthy eating? nutrition blog post explores this topic.
There is a lot to gain by simply ensuring you have a healthy and varied diet which contains plenty of fibre. In addition, make sure that your body weight is at a healthy level, with abdominal fat as low as possible, and that you exercise on a daily basis. Meat may be part of the diet, but should only be enjoyed in moderate quantities. For ethical and sustainable reasons, meat which has been produced with regard to animal welfare or game meat is preferred. Processed meat as well as alcohol should only feature in the diet on occasion and not a regular basis. It is not absolutely certain, but it is likely, that garlic, milk and calcium have a protective effect. The data situation regarding the protective effect of fruit and vegetables is even less certain, beyond what is known about the positive impact of their high-fibre content. Foodstuffs rich in vitamin D are often associated with a protective effect. In this case the data available is also insufficient, as is the assumption that cheese, iron-rich foods, animal fats and sugar facilitate the development of colorectal cancer.
Sources
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