Diet in cancer prevention

In Europe, approximately one in four deaths is caused by cancer, making the disease the second cause of death in the European countries (after cardiovascular disease). Most people die from following types of cancers: lung, gastrointestinal, breast and prostate. Men most often suffer from lung cancer, prostate cancer and colorectal cancer. The most common cancers in women are breast cancer, colorectal cancer and lung cancer.

While everyone has heard of saturated fatty acids, cholesterol and other nutrition-related aspects of the prevention of cardiovascular diseases, the average person knows little about diet’s relationship with the occurrence of certain types of cancer.

About 40% of cancers could be prevented through proper diet and regular physical activity

Genes versus lifestyle

According to the latest available data, only a small percentage of cancer is down to our genes only. WCRF and AICR estimate this figure to be  about 5% to 10%, whereas poor diet, overweight, obesity and lack of physical activity are responsible for 3 to 8 times more cancer incidence than genetic inheritance[2].

It is worth to quote the statement of Dr Rachel Thomson, WCRF’s Deputy Head of Science: ‘The occurrence of cancer in the family is an important information for patients, but purely genetic predisposition to cancer is relatively uncommon. Specific genes responsible for breast cancer or colon cancer have been identified, but occur rarely and they only cause very small percentage of cancers. On the other hand, approximately one third of the most common cancers could be prevented by a proper diet, physical activity and maintaining normal body weight. People with a genetic predisposition to cancer should especially pay attention to the lifestyle, as leading a healthy life can significantly reduce the risk of disease.’

Information on the share of environmental factors in causing cancer was obtained from the study of migrants and observation of Asian countries, in which changes in the incidence of cancer in the last 60 years took place too quickly that it can be attributed to genetic determinants.

For example:

·       The incidence of breast cancer and colorectal cancer has increased three times in the second generation of Japanese immigrants to the United States, which according to scientists is related to the adoption of American lifestyle, including eating habits[3].

·       Migrating to the U.S. and the length of residence in the US is an independent risk factor for prostate cancer among men born in Asia is which suggests a strong influence of American lifestyle on the risk of developing this disease (the longer the Asians live in the United States, the higher risk of prostate cancer they have)[4]

·       Incidence of prostate cancer back in the 90’s of the last century was 15 times higher in the U.S. than in some Asian countries[5]. Nowadays these differences are obliterated mainly due to the increasing prevalence of so-called 'western lifestyle', including diet on the continent.

·       These days, China experiences unprecedented epidemic of breast cancer; in 2008, there were 10 to 60 cases of breast cancers in 100 000 women; it is estimated to increase to 100 in 100 000 women in 2021[6], which is explained by scientists as a result of lifestyle changes, including diet on the continent.

Prevention

After each WCRF and AICR scientific report, the media in the United States and Great Britain as well as other countries such as the Netherlands, France and China, communicate openly about the possibility of cancer prevention by changing our eating habits, while the media in our country do not pay much attention to this topic.

And it is something worth fighting for. In 2009 the World Cancer Research Fund presented a report[8] which is a summary of all existing knowledge on the link between the lifestyle and cancer. This report informs what percentage of cancers could be avoided by a healthy way of life (proper diet, keeping proper body weight and physical activity). These percentages are as follows:

·       about 45% of all large intestine cancers

·       about 38-42% of all breast cancers

·       about 11-20% of all prostate cancers

·       about 56-70% of all endometrial cancers

·       about 45-47% of all stomach cancers

·       about 40% of all pancreas cancers

·       about 35% of all lung cancers

·       about 70-75% of all esophageal cancers

·       about 65% of all oral cavity, pharynx and larynx cancers

·       about 16-21% of all gallbladder cancers

·       about 15-17% of all liver cancers

·       about 19-24% of all kidney cancers.

The above values ??are based on studies of the British society and do not take into account smoking as the leading single cause of cancer incidence, therefore leading a healthy lifestyle (together with not smoking) could prevent the development of even greater number of cancers.

Cancerous food

Scientific studies aimed at finding the causes and factors that increase the risk of diseases are very tedious. It takes a lot of evidence in order to be able to determine the long-term effects of various substances on the human body. So far four groups of compounds that can be found in our food were classified as carcinogenic. They are aflatoxins, which are present in mouldy food, heterocyclic amines, formed during high temperature food processing (for example, during grilling or baking foods rich in protein – meat, including fish), n-nitrosamines that are found in processed meat and fish, along with polycyclic aromatic hydrocarbons.  The latter are formed in grilled and smoked meat, fish, as well as burnt products and those fried in oil. All the above listed substances can damage our DNA and thereby cause formation of the tumour cells.

Another product increasing the risk of cancer is alcohol (including red wine!), which is proven to be a risk factor for oral cavity, larynx, pharynx, esophagus, breast, colon, and probably liver cancers. Even moderate alcohol consumption can significantly increase the risk of breast cancer. NIH-AARP Diet and Health Study followed  185 000 women for 13 years. Comparing to nondrinking women, those who drank 1-2 units of alcohol per day were 32% more likely to have breast cancer (receptor-positive), and those drinking 3 units per day – 51%. WCRF and AICR scientists recommend eliminating, or at least limiting alcohol intake to a maximum of two units per day for men and one for women. “Unit” is a portion of alcohol containing 10-15 g of pure compound, that is: a small beer (330 ml), a small glass of wine (125 ml) and 25 ml of vodka, whisky or brandy.

In recent years scientists also examined meat products (cold meats, frankfurters, sausages, etc.) and red meat (beef, veal pork, lamb). In 2007 the World Cancer Research Fund in their comprehensive report recognized these groups of products as the only ones that can be defined as dietary risk factors for colorectal cancer. This argument was confirmed in 2011, in an update of this report.

Quoting AICR: even minimum amount of processed meat (such as cold meats) increases the risk of colon cancer, which grows with each bite ingested. Processed meats increase the risk of colon cancer by about 36% with every 100g (4-5 slices of ham) daily consumption.

Dairy products are still subject to doubts. On one hand, a diet high in calcium appears to protect against colon cancer, on the other hand, there are suspicions that regular consumption of dairy products may increase the risk of prostate cancer. For that reason Harvard scientists encourage meeting your calcium needs from other, non – dairy products, for example, cruciferous vegetables (broccoli, cauliflower and cabbage), legumes, sesame seeds, almonds, and calcium-fortified vegetable milk (such as soy, rice, etc.)[9].

Cancer promoters

Studies concerning link between cancer and diet, not only focus on individual substances or products, but also the overall diet.

Our diet as a whole (unlike its particular elements) influences the processes that may promote the development of cancers, such as chronic inflammation[10]^,[11], increased concentration of certain hormones[12] and activating or "disabling" certain genes[13]. This effect of diet on cancerous processes is called the promotion of the existing tumor cells.

So-called promoter of the neoplasia is excessive fat, protein and processed carbohydrates in the diet, which is a typical Western (including Polish) eating manner. Consumption of food of animal origin, especially fatty meats and cheeses, as well as highly processed products, such as sweetened soft-drinks and oils, increases inflammatory processes no longer than 30-90 min after a meal.[14]^,[15]. Inflammation encourages the reproduction of existing cancer cells and prevents from their death. Excess supply of protein in the diet, particularly animal protein, increases the concentration of a certain growth factor, IGF-1 (insulin-like growth factor 1)[16], which promotes the multiplication of cancer cells and may block their death[17].

Another strong promoter is excess body fat. According to WCRF the risk of cancer increases not only because of obesity, but also overweight and the level of body fat which is considered to be innocuous. Research has shown that Body Mass Index within the upper limit of the norm may increase the risk. Widely acknowledged standard is 18.5-24.9. In cancer prevention the ideal BMI should be lower than 23. Cancers of which the risk increases due to the excessive weight include endometrial, esophagus, pancreas, kidney, gallbladder, breast and colon cancers.

Therefore, all the products, the consumption of which favours the overweight and obesity, that is products with a high energy density (=energy (calories) – per unit mass), indirectly increase the risk of cancer. These include fatty meats, fatty cheeses, and added fats such as butter, margarine, oils, as well as products with a high content of sugar and fast food products. They also displace low-processed vegetable products (fruits, vegetables, cereals, legumes) which have nutritious properties and low energy density (that is a relatively small number of calories per unit volume), therefore they promote lean figure.

What protects us?

Vegetables, fruits, legumes, nuts and seeds contain many of the protective factors. These are antioxidants and other phytochemicals (e.g.: flavonoids, isoflavones, glucosinolates, carotenoids). They inhibit the conversion of potentially carcinogenic substances to carcinogenic and reduce the impact of damage to the genetic material (which may lead to the development of cancer)[18]. Substances that are found in vegetables and fruits "extinguish" inflammations by blocking the activity of genes involved in inflammatory processes[19]. They may also cause the death of cancer cells, block the formation of blood vessels supplying the tumor, and enhance detoxification of carcinogens. Diet based on low-processed plant products contains a lot of them, it is also a source of fibre, which directly protects against colon cancer[20] and breast cancer[21], and indirectly reduces the risk of other malignancies thus it helps to stay slim and reduces inflammatory processes in the body.

Such a diet reduces the supply of "promoters of cancer" because it delivers adequate levels of protein (avoiding excess of this compound) and relatively little fat, provided that it is not added as an oil, margarine or butter. On top of vegetables and fruits it is also recommended to consume moderate amounts of nuts and seeds, low-fat dairy products and skinless white meat (if the latter two groups are eaten).

Hundreds of studies have shown that a diet based on plant products protects against many cancers. Therefore, it is highly recommended by the WCRF, AICR and other oncological organizations in cancer prevention. The World Health Organization have been claiming for many years that in order to prevent chronic disease (not just cancer), people should eat mostly vegetables, fruits, legumes and whole grains, and the addition of food of animal origin should be minimal[22].

Diet is not the only factor

What else should we pay attention to? Another recommendation is at least 30 minutes of physical activity per day. In addition to helping to maintain a healthy weight, it strengthens the immune system and reduces the risk of many diseases – from cancer, through cardiovascular disease and diabetes to osteoporosis. And it does not necessarily have to be sports – working in the garden, cleaning the house and active play with children also count.

Diet and the secondary prevention of cancer

Although the data on the secondary prevention of cancer is not as abundant as the data on the primary prevention, available findings suggest that lifestyle factors such as regular alcohol consumption, smoking, overweight and obesity, lack of physical activity as well as the so-called "Western diet", i.e. diet rich in meat (especially red meat), fats, processed carbohydrates (pastries with white flour, sweets, etc.) and eggs, increases the risk of colon cancer recurrence[23], breast cancer recurrence[24]^,[25],[26], prostate cancer recurrence[27] and probably also other malignancies [28]. Research also suggests that the same elements of lifestyle that are recommended in the prevention of cancer, such as smoking cessation, following a plant-based diet, maintaining a healthy weight and regular physical activity can have a positive effect on the survival of patients with previously diagnosed cancer and reduce the risk of recurrence of certain cancers.

The text was prepared for the Polish Foundation: ‘We know what we eat’. The main objective of the Foundation is to provide reliable and evidence – based information about nutritional medicine to the society, focusing on possibilities of prevention and treatment of diseases through nutrition.

The whole literature is with the author.