The relationship between Red Meat Consumption and Colon Cancer
Nutritional epidemiology provides evidence about the diet-disease relationship to inform Public Health Nutrition (PHN) and enable the development of prevention methods [Boeing, 2013].
Almost 60% of global colorectal cancer (CRC) cases are seen in developed countries [Ferlay et al., 2010]. In the UK, CRC is the fourth most common cancer; accounting for an incidence rate of 47 per 100,000 in 2011 [CRUK, 2014a].
The WCRF/AICR  recognise the complexities of determining associations between diet and cancer, and conclude that red and processed meat (RAPM) are ‘convincing’ causes of CRC. This is reinforced by subsequent meta-analyses by Chan et al.  and Xu et al. . In contrast, Alexander and Cushing  suggest there is inadequate evidence to support this relationship .
The aim of this essay is to critically appraise two cohort studies by Norat et al.  and Cross et al. , observing the relationship between RAPM consumption and CRC risk. These studies have been selected due to their large sample size and robust study design. Since CRC is largely influenced by diet [Willett, 2005], understanding these influences will enable development and implementation of PHN strategies at a national and local level [Webster-Gandy, Madden and Holdsworth, 2012].
Cohort studies are the strongest observational design for diet and cancer [Gibney et al., 2004]. Although randomised controlled trials (RCTs) are considered the ‘gold standard’ of quantitative research methods [Aveyard and Sharp, 2009], they are not always appropriate [Morrow, 2010]. Since cancer develops slowly, applying intervention trials can be difficult [Gibney et al., 2004]. It may also be unethical to use a RCT, as some participants would not receive the potentially beneficial treatment [Sanson-Fisher et al., 2007]. Cohort studies however are considered to be ethical, and are useful for establishing a sequence of events [Heneghan and Badenoch, 2006]. In contrast, they do involve enrolling numerous participants which is costly [Willett, 2013]. There is also potential for selection bias, information bias and confounding bias which can reduce the reliability and validity of the findings [Healey and Devane, 2011].
Both studies used Cox regression to adjust for confounders. CRUK [2014b] outline the dietary and lifestyle factors believed to be associated with CRC risk. Both studies have failed to account for some of these factors, which could lead to an inappropriate assumption that the exposure increases disease risk [Healy and Devane, 2011].
In the XXXX study, cooking methods were not considered, even though certain methods have been linked with carcinogen production [WCRF /AICR, 2007]. Genetic susceptibility was also not accounted for, despite the evidence of an association between family history and CRC [Johns and Houlston, 2001]. Additionally, socioeconomic factors were not taken into account, despite the positive association between deprivation and CRC incidence in males [PHE, 2014].
In the YYYY study, the highest consumers of red meat also had other CRC risk factors. Therefore, residual confounding may have contributed to the positive associations observed. Additionally, 42.8% of women reported use of hormone replacement therapy (HRT), which wasn’t adjusted for, even though HRT is believed to reduce CRC risk [CRUK, 2014b].
Alexander, D.D. and Cushing, C.A. (2011) ‘Red meat and colorectal cancer: a critical summary of prospective epidemiological studies’. International Association for the Study of Obesity. 12(5), pp. e472-e493.
Aveyard, H. and Sharp, P. (2009) A beginners guide to evidence based practice in health and social care. Berkshire: Open University Press
Boeing, H. (2013) ‘Nutritional epidemiology: New perspectives for understanding the diet-disease relationship?’ European Journal of Clinical Nutrition. 67, pp. 424-429.
Cancer Research UK (CRUK) (2014a) Bowel Cancer Incidence Statistics. Available at: http://www.cancerresearchuk.org/cancer-info/cancerstats/types/bowel/incidence/
Cancer Research UK (CRUK) (2014b) Bowel Cancer Risk Factors. Available at: http://www.cancerresearchuk.org/cancer-info/cancerstats/types/bowel/riskfactors/bowel-cancer-risk-factors
Chan, S.M., Lau, R., Aune, D., Vieira, R., Greenwood, D.C., Kampman, E. and Norat, T. (2011) ‘Red and Processed meat and Colorectal Cancer Incidence: meta-Analysis of Prospective Studies’. PloS ONE. 6(6), pp. 1-11.
Cross, A.J., Leitzmann, M.F., Gail, M.H., Hollenbeck, A.R., Schatzkin, A. and Sinha, R. (2007) ‘A Prospective Study of Red and Processed Meat Intake In Relation to Cancer Risk’. PLoS Medicine. 4(12), pp. 1973-1984.
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Gibney, M.J., Margetts, B.M., Kearney, J.M. and Arab, L. (2004) Public Health Nutrition. Oxford: Blackwell Science.
Healy, P. and Devane, D. (2011) ‘Methodological considerations in cohort study designs’. Nurse Researcher. 18(3), pp. 32-36.
Heneghan, C. and Badenoch, D. (2006) Evidence-based Medicine Toolkit (pdf). 2nd edn. Massachusetts: Blackwell Publishing. Available at: http://eprints.kmu.ac.ir/2227/1/Evidence-Based%20Medicine%20Toolkit%20-%202nd%20Edition.pdf
Johns, L.E., Houlston, R.S. (2001) ‘A systematic review and meta-analysis of familial colorectal cancer risk’. Am J Gastroenterol. 96(10), pp. 2992-3003.
Morrow, B. (2010) ‘An overview of cohort study designs and their advantages and disadvantages’. International Journal of Therapy and Rehabilitation. 17(10), pp. 518-523.
Norat, T., Bingham, S., Ferrari, P., et al (2005) ‘Meat, fish, and colorectal cancer risk: the European Prospective Investigation into cancer and nutrition’. J Natl Cancer Inst. 97(12), pp. 906–916.
Public Health England (PHE) (2014) National Cancer Intelligence Network: Cancer by Deprivation in England (pdf). Available at: file:///C:/Users/Megan/Downloads/Cancer_by_Deprivation_in_England_1996_2011.pdf
Sanson-Fisher, R.W., Bonevski, B., Green, L.W. and D’Este, C. (2007) ‘Limitations of the Randomised Controlled Trial in Evaluating Population-Based Health Interventions’. American Journal of Preventive Medicine. 33(2), pp. 155-161.
Willett, W.C. (2005) ‘Diet and cancer: an evolving picture’. JAMA. 293(2), pp.233-234.
Willett, W.C. (2013) Nutritional Epidemiology. 3rd edn. New York: Oxford University Press.
Webster-Gandy, J., Madden, A. and Holdsworth, M. (2012) Oxford Handbook of Nutrition and Dietetics. 2nd edn. Oxford: Oxford University Press.
World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) (2007) Food, nutrition, physical activity and the prevention of cancer: a global perspective (pdf). Available at: http://www.dietandcancerreport.org/cancer_resource_center/downloads/Second_Expert_Report_full.pdf
Xu, X. Yu, E., Gao, X., Song, N., Liu, L., Wei, X. Zhang, W. and Fu, C. (2013) ‘Red and processed meat intake and risk of colorectal adenomas: A meta-analysis of observational studies’. International Journal of Cancer. 132(2), pp.437-448.
I am module lead for Nutritional Epidemiology module. This assessment is a challenge for the students as it tests their critical writing skills (and nutrition as a subject area that provides many complexities with this skill). This essay excerpt is taken from a student who achieved a first class mark for this assessment. This essay (of which excerpts are shown) was well structured, with good use of a range of referenced sources, which were well integrated to demonstrate good understanding of epidemiology concepts as well as excellent skills in critical appraisal of the evidence.