Should We Stop Eating Meat - Term Paper Example

Should We Stop Eating Meat? According to the World Health Organization, 30 percent of all cancers in the Western World and 20 percent of them indeveloping countries are due to dietary factors (Cancer Project, 2005). When researchers of cancer started to search for causes of cancer in the diet, the most significant finding that was observed was that those who did not consume meat were less likely to develop cancer. Infant, many studies in the Europe have proved that vegetarians are 40 percent less likely to suffer from cancer when compared to those who consumed non-vegetarian food. Studies conducted on Adventist population in which there were no confounding factors like life style habits and smoking and alcohol intake, have clearly shown that vegetarians are at much less risk than non-vegetarians with respect to developing cancer (Cancer Project, 2005). Intake of meat, especially the red meat has been associated with cancers. Meats are usually cooked in high temperatures like grilling or pan-frying, which increase the content of polycyclic aromatic hydrocarbons or PAH and heterocyclic amines or HCA, both of which are carcinogenic. HCAs are formed from reaction of creatinine, creatine, sugars and amino acids. Higher the temperatures used for cooking and longer the periods of cooking, greater are the chances of production of HCAs. The types of meats and the method of cooking also influence the the formation of HCA. Several animal studies have shown the association between HCAs and various types of cancer like those of mammary glands, colon, lung, fore stomach and prostate. The recent detection of HCA-DNA adducts in various tissues of humans implies that human tissues are vulnerable to HCAs (Zheng and Lee, 2009). Thus, it is clear that consumption of meat, especially that is well cooked and red is associated with risk of cancer. Several hypotheses have been drawn to explain such an association. The first explanation is that meat does not have any fiber and several other nutrients that are protective against the development of cancer. The second hypothesis is that meat contains significant amount of animal protein, saturated fat and sometimes carcinogenic compounds which are formed during the process of cooking. The third reason is that meat has very high fat content and when consumed, increases the production of hormones, which ultimately contribute to hormone related cancers like the prostate cancer and the breast cancer. While the first two hypotheses have been proved scientifically, the third hypotheses has been refuted by several large prospective cohort studies (Zheng and Lee, 2010). Several cancers have been attributed to increase in meat consumption and they are cancers of kidney, breast, prostate, colon and pancreas. The past two decades have seen an increase in the number of epidemiological studies and have examined the role of HCAs in the development of various types of cancers in the human beings. Since these compounds are produced only when meat is cooked under high temperatures, most epidemiological studies use intake of high-cooked meats as surrogate measures of exposure to high levels of HCAs (Zheng and Lee, 2009). One of the deadliest cancers in humans, the pancreatic cancer has been attributed to increased intake of high done meat. 3 major epidemiological studies and one cohort study has evaluated the potential role of HCA in the risk of pancreatic cancer. One epidemiological study in Minnesota by Anderson et al (2002, cited in Zheng and Lee, 2009) found a positive association between intake of high done meat and risk of cancer. The study also found several carcinogens in the meat, BaP, PhIP and DiMeIQx that are associated with etiology of pancreatic cancer. In yet another recent study by Lie et al (2007, cited in Zheng and Lee, 2009), similar association was found between high done meat and risk of cancer. In a large cohort study by Stolzenberg-Solomon et al (2007), the researchers evaluated the association between meat, methods of cooking meat, mutagens associated with intake of meat and exocrine pancreatic cancer. From the study, it was evident that red meats that are cooked completely at high temperatures were associated with risk of pancreatic cancer in men. For some reason, such a risk was not associated with women. When the men consumed highest tertile of meat, like the grilled meat or broiled meat or barbecued meat, the risk of pancreatic cancer doubled. This study revealed that exposure to high done meat increases the risk of pancreas by two times. The association between prostate cancer and increased intake of highly done meat has also been studied. Studies have shown that while there is no difference between cancer risk due to white meat or red meat and elevated risk of prostate cancer, definite association has been found between increased intake of meat that is very well done and prostate cancer. Until now, several studies, including 2 cohort studies have studied the association between high done meat and risk of prostate cancer. One large study by Cohort et al (2005; cited in Zheng and Lee, 2009), a prospective cohort study followed up 29,000 adult men who took part in the initial cancer screening programme, 868 cases of prostate cancer were detected. Though this study could not find any association between intake of white or red meat and risk of cancer, definite association was found between intake of high done meat and prostate cancer. In a study by Koutros et al (2008), the researchers prospectively observed the association between types of meats, methods used for cooking of meat, doneness of meat and mutagens of meat with reference to prostate cancer. From this study, it was evident that there is no association between the type of meat or the method of cooking with risk of cancer. However, intake of meat that is either well done or very well done is associated with 1.26 percent risk of prostate cancer. The compounds that were significant with respect to risk of cancer were 2-amino-3,8-dimethylimidazo-[4,5-b]quinoxaline and 2-amino-3,4,8-trimethylimidazo-[4,5-f]quinoxaline. One small hospital-based study reported lack of association between prostate cancer and high done meat. This was a case-control study and experts opine that this study was subjected to potential biases in areas of patient selection and assessment of exposure (Zheng and Lee, 2009). The incidence of breast cancer is higher in countries where there is increased consumption of fat from animal products like dairy and meat. In Japan, since traditionally there is decreased intake of fat, breast cancer incidence rates are low. Some studies have shown that when Japanese girls are raised on American diet, the chances of breast cancer increase. Women with increased intake of well-done meat are at 4.6 fold increase in breast cancer. Several genes like NAT1 and 2 have been identified that increase the association between increase in meat intake and development of cancer (Zheng and Lee, 2010). 3 major studies have found association between exposure to HCA or high cooked meat and risk of breast cancer. One study was a small hospital based case control study in which benign breast disease patients were taken as controls, no positive association was found between breast cancer and intake of high done meat. In the other 2 studies, which were done on post menopausal women and the controls were normal women in post menopause phase, positive association was found between intake of high done meat and risk of breast cancer (Zheng and Lee, 2009). In a study by Zhen et al (cited in Zheng and Lee, 2009), it was reported that consistent intake of meat in women increases the risk of development of breast cancer by 4.6 fold. Based on reports from this study, another study by Sinha et al (2006; cited in Zheng and Lee, 2009) evaluated and demonstrated a clear association between PhIP and breast cancer and not other mutagens. Most epidemiological studies which assessed the risk of colon cancer due to ingestion of high levels of well-done meat have proven increase in risk of colon cancer. Seven major studies have been done to study the relationship between risk of cancer and intake of meat. All of them, except the Sweden based study in the early years have reported positive association between colorectal cancer and intake of meat. Kampnam (1999; cited in Zheng and Lee, 2009) reported 30 percent increase in risk of cancer. This study also reported that the association between cancer risk and mutagen index was modifiable by NAT2 gentypes. Such a gene-diet interaction was replicated in another study by LeMarchand et al (2001; cited in Zheng and Lee, 2009). The mutagens for which definite association with risk of cancer were found were, MEIQx and DiMEIQx. There has been some research to ascertain the role of high done meat in the development of adenomatous polyps. Most studies have infact reported such an association between colon polyps and increased intake of meat. Increased intake of meat has been associated with other cancers too like esophageal cancer and stomach cancer. The role of HCAs in stomach cancer is a much controversial issue. In the esophagus, squamous cell carcinoma has been attributed to increased intake of meat and not adenocarcinoma. But one study has suggested the role of meat even in adenocarcinoma. Study by Sinha et al (1998; cited in Zheng and Lee, 2009) has associated with consumption of fried red meat or well done meat with risk of lung cancer. This is in concordance with studies that have reported association between MEIQx and risk of lung cancer. Such an association has been demonstrated in animal models too. Several experiments, in vivo and in vitro have clearly proven the fact that HCAs, found in high done meat, are potent mutagenic agents and can induce cancers in several parts of the body, not only in animal models, but also in humans. Increasing number of epidemiological studies, especially over the past 10 years have associated intake of well-done meat and exposure to HCA with risk of various types of cancers. Many studies have also studied the interaction between exposure to HCA or intake of well done meat and genetic polymorphisms in metabolizing enzymes of carcinogens towards risk of development of cancer. The statistical power of these studies are limited because of small sample size and bias. However, most studies have in detail, assessed the risk of cancer with reference to methods of cooking of meat and intake of high-done meat and from these studies it is very clear that intake of meat increases the chances of developing cancers of various tissues like prostate, breast, stomach, colon, rectum, esophagus, pancreas and lungs. Thus, consumption of meat is not advisable and dieticians and health providers must advise their clients about this. References Cancer Project. (2005.). Cancer prevention and survival. Retrieved on 27th November, 2010 from http://www.cancerproject.org/survival/cancer_facts/meat.php Koutros, S., Cross, A.J., and Sandler, D.P. (2008). Meat and meat mutagens and risk of prostate cancer in the Agricultural Health Study. Cancer Epidemiol Biomarkers Prev., 17(1), 80-7. Stolzenberg-Solomon, R.Z., Cross, A.J., Silverman, D.T., et al. (2007). Meat and meat-mutagen intake and pancreatic cancer risk in the NIH-AARP cohort. Cancer Epidemiol Biomarkers Prev., 16(12), 2664-75. Zheng, W., and Lee, S. (2009). Well-done Meat Intake, Heterocyclic Amine Exposure, and Cancer Risk. Nutr Cancer, 61(4), 437–446. Read More