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Q. Dietary factors that increase or decrease the risk of gastro-intestinal cancers.
The gastro-intestinal (GI) tract is known to be one of the most frequent sites of cancer and many different infections since it is constantly being exposed to different bacteria and virus. It mainly consists of the stomach, pancreas, small and large intestines and the oesophagus. It plays an important role in the digestion along with the absorption of food and many fluids, electrolytes and vitamins. Just like the other parts of the body, the organs in the digestive system consist of cells and when these cells grow and reproduce uncontrollably an individual suffers from cancer. The cause of cancer can be either from genetic factors, which are germline mutations present in every cell or somatic alterations found in tumour cells, or environmental factors which could be physical, chemical or biological. Cancers arising within the GI tract are linked initially with an immune component and secondly in their maintenance. Gastrointestinal cancers include the oesophageal, gastric, hepatobiliary (liver cancer), pancreatic and the colorectal cancer. The most common symptoms associated with GI cancers include nausea, vomiting, diarrhoea and constipation. Some treatments to cure these cancers are available. Patients with oesophageal cancer are sometimes treated with radiotherapy and colon, gastric and liver cancer patients go through surgeries.
Diet is said to play a major role in a number of cancers. In the late 1970’s an interest about the relationship between diet and cancer began to emerge. Almost by 1980, numerous researches conducted in various parts of the world had pointed out that diet and other lifestyle factors have quite a role to play in the development of cancer. The recent changes in diet have overwhelmingly affected the rates of disease. Many food products contain dietary genotoxins which are formed by contaminating moulds, products of storage or fermentation of food and food additives (Bower, & Jonathan, 2011). Excess body fat is an important risk factor for cancers of the pancreas, colon and oesophagus, since fats increase the production of bile acids and sterols and can produce carcinogenic compounds. Around 1982, the committee in diet, nutrition and cancer of the National Academy of Sciences declared that it had enough evidence to confirm that high fat consumption was linked to an increase in colon cancer (Bendich, 2010). In one of the prospective studies carried out among 89,000 women in England by Colditz, Rosner, Stampfer, Speizer & Willett (1990) a positive correlation was identified between the consumption of red meat (processed meat) and risk of colorectal cancer. 9 more studies conducted in the United States found a positive relationship. A possible reason for this could be due to the presence of high content of heme iron or nitroso compounds in the red meat which are considered to be carcinogenic (Bendich, 2010). The nitrites are produced via oxidation of nitric oxide and reduction of nitrate by the bacteria in the GI tract (Bryan, Hord & Tang, 2009). The nitrite then reacts with amines and amides to produce nitrosamines and nitrosamides respectively. And these two compounds constitute the N-nitroso compounds which are known to cause cancer. Many early studies conducted in the 1960’s by Hirayama of approximately 268,000 Japanese have suggested that a high intake of fruits and vegetables would decrease the risk of a wide range of cancers. Between 1964 and 1995, 31 dietary studies were conducted out of which 26 studies examined different food groups and in that 24 found a decreased risk of stomach and oesophageal cancer with a high intake of one or more fruits or vegetables. However, more recent cohort studies have revealed either a weaker or no relation between the two, but these findings would require an eventual authentication before any conclusion can be given. Micronutrients from various fruits/vegetables are strongly believed to decrease the risk of gastric cancer as well. According to Graham, high consumption of Vitamin C (oranges, grapefruits, lemons), β-carotene (sweet potato, carrots and spinach) and also Vitamin E/Selenium (nuts, avocados) have proved to trim down the risk of gastric and oesophageal cancer. The mean plasma levels of vitamin C and carotene is significantly found to be lower in people who die of gastric cancer (Bendich, 2010). This could be because both Vitamin C and β-carotene are antioxidants and can neutralize free radicals thereby preventing oxidative damage to DNA and causing cancer. Folate may also be associated to cancer since a low folate status could damage the DNA repair capacity which is one of the noted risk factor for human cancers. Another micronutrient which has shown to reduce the risk of cancer is calcium taken from either food or supplements. Low-calcium intake has been associated with the risk of colon cancer in large prospective studies even though the data are inconsistent (Bendich, 2010). In ‘Preventive Nutrition’, Bendich states that the mechanism of action of calcium is thought to be via the reduction in bile acids that are thought to be carcinogenic. An article by Hill discussed the relation between cereals, dietary fibre and cancer found out that cereals, mainly rice, did have a protective effect on cancer. Another article by Graham supports the inverse relation between dietary fibre and cancer of the colon. One of the possibilities could be that large amounts of fibre in the diet dilute any carcinogen going through the gut and therefore reduce the opportunity for any carcinogen to act on the wall of the gut (Burkitt & Trowell, 1975). Dietary ascorbic acid which can be obtained from citrus fruits, tomatoes, kiwis and many berries can act as an antioxidant and reduce carcinogenic nitrosamines formation in the stomach (Graham, 1983). Another study done by Higginson had proved the reduction in risk of gastric cancer with an increased intake of ascorbic acid. In an article ‘Pickled Food and Risk of Gastric Cancer’ the consumption of salty and pickled foods has been associated with stomach cancer, since the action of salt facilitates the action of carcinogens and thus salt is known to act like a carcinogen- meaning a substance involved in causing cancer. Some pickled foods contain N-nitroso compounds mainly nitrosamides which are direct-acting carcinogens and therefore they could act in the stomach if produced there (Mirvish, 2006). Alcohol is also linked with gastric cancer too, however many studies conducted in various countries have yielded mixed results. A study carried out in 1990 in Los Angeles reported positive associations while another research done in Japan found no amplified risk of gastric cancer associated with the consumption of alcohol (Bendich, 2010). In addition to that, tobacco smoke and cancer risk had also been reviewed and it was concluded that current smokers were at increased risk for both cardia (upper opening of the stomach) and noncardia stomach cancer since tobacco smoke is also known to contain many carcinogenic compounds like nicotine and nitrosamines (Cho, & Seitz, 2009).
Table 1: Lists the different dietary factors which can be associated with different cancers of the GI tract.
Factors associated with decreased risk of cancer
Factors associated with increased risk of cancer
Table 1 provides an overall conclusion of the factors linked with the decreased/increased risk of the GI cancers showing how different dietary habits can link to various cancers. Just to sum up and prove the above points based on diet and cancer, an article ‘Association of Dietary patterns with cancer recurrence and survival in a large group of stage III colon cancer patients’ published in 2007 had examined the influence of two different dietary patterns, western and prudent. A western diet which had more of red and processed meat, sweets refined grains and the prudent diet containing all the fruits, fish, vegetables and whole grains. The results concluded that a higher intake of a western diet may be associated with a higher risk of cancer recurrence. Therefore it can be assumed that the most consistent recommendations to prevent different cancers could be by maintaining a healthy diet, eating more fruits, vegetables, grains and less high-fat foods and meat in combination with regular exercise as well as avoiding smoking, tobacco and alcohol. A latest study carried out showed that the rate of gastric cancer has been declining in many countries with the most probable reasons relating to improved living conditions particularly improved sanitation, water quality, food hygiene and a reduction in smoking (Jankowski, 2011). Recent advances in molecular biology have yet to contribute significantly to dietary recommendations, but hopefully in the future these approaches may provide some endpoints and enhance our understanding of the mechanisms by which dietary factors influence cancers. Some of the researches mentioned in this essay are observational studies; there are currently many research work, studies, experiments being done in order to prove all the points on diet and cancer.
- Bower, M. & Jonathan, W. (2011). Lecture Notes Oncology. (2nd ed.). London: John Wiley & Sons.
- Bendich, A. (2010). Preventive Nutrition. (4th ed.). New York: Springer.
- Colditz, G.A, Rosner, B.A, Stampfer, M. J, Speizer, F.E & Willett, W.C. (1990). Relation of meat, fat and fiber intake to the risk of colon cancer in a prospective study among women, 323 (24), 1664-1672.
- Bryan, N.S, Hord, N.G. & Tang, Y. (2009). Food Sources of nitrates and nitrites. The physiologic context for potential health benefits, 90 (1), 1-10.
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- Hill, M.J. (1998). Nutrition Research. Cereals, Dietary Fibre and Cancer, 18 (4), 653-659.
- Burkitt, D.P & Trowell, H.C. (1975). Refined carbohydrate foods and disease: some implications of dietary fibre. New York: Academic Press.
- Mirvish, S.S. (2006). Effects of Vitamins C and E on N-Nitroso Compound Formation, Carcinogenesis and Cancer, 58 (8), 1842-1850.
- Cho, H.C. & Seitz, H.K. (2009). Cancer Epidemiology. Contribution of Alcohol and Tobacco Use in Gastrointestinal Cancer Development, 472 (2), 217-241.
- Fuchs, C. S., Hantel, A., Hollis, D., Hu, F.B., Mayer, R.J., Meyerhardt, J.A., Nelson, H., Niedzwiecki, D., Saltz, L.B., Thomas, J. & Whittom, R. (2007). Association of Dietary Patterns with Cancer Recurrence and Survival in Patients with Stage III Colon Cancer, 298 (7), 754-764.
- Jankowski, J. (2011). Inflammation and Gastrointestinal Cancers. London: Springer Fachmedien.
- Forman, D., Islami, F., Kamangar, F & Ren, J. (2012). Cancer Epidemiol Biomarkers & Prevention. Pickled Food and Risk of Gastric Cancer- a Systematic Review and Meta-analysis of English and Chinese Literature, 23 (11), 905-915.