Sunday, May 17, 2015

Fresh (!) Red Meat Acquitted - Overgeneralized Accusations that Red Meat Consumption Triggers Cancer Overlooks Influence of Processing & Other Confounding Factors

I guess if someone finally dared to do this study, there would be a linear or exponential association between the number of processing steps red meat has undergone and the increase in cancer risk from regular consumption. Stay away from cheap bacon, sausages & co.
The potential relationship between red meat consumption and colorectal cancer (CRC) has been the subject of scientific debate. In fact, you will remember that I have addressed the issue repeatedly and in various articles. If you read all or at least some of the articles you will also be aware of the fact that the evidence against red meat is of observational nature and has a high degree of resulting uncertainty.

Dominik D. Alexander's and his colleagues's objective was thus to conduct a systematic quantitative assessment of the epidemiologic literature. Specifically, they updated and expanded their previous meta-analysis by integrating data from new prospective cohort studies and conducting a broader evaluation of the relative risk estimates by specific intake categories.
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Data from 27 independent prospective cohort studies were meta-analyzed using random-effects models, and sources of potential heterogeneity were examined through subgroup and sensitivity analyses. In addition, a comprehensive evaluation of potential dose-response patterns was conducted.
Table 1: Meta-analysis of prospective studies of red meat consumption and colorectal cancer (Alexander. 2015)
In the meta-analysis of all cohorts, a weakly elevated summary relative risk was observed (1.11, 95% CI: 1.03–1.19); however, statistically significant heterogeneity was present. Furthermore
However, in the model that included studies of fresh red meat (n D 17 studies independent of processed meat items), the SRRE dropped to 1.05 and was no longer statistically significant (95% CI: 0.98–1.12), and the model was less heterogeneous (p-H D 0.328). Of 13 of these studies that explicitly defined red meat, the SRRE was 1.04 (95% CI: 0.98–1.14, p-H D 0.263). [...] Stronger (and more heterogeneous) associations were observed in meta-analyses of studies conducted in North America (SRRE D 1.18, 95% CI: 1.05–1.32), compared with studies published in other countries (SRRE D 1.07, 95% CI: 0.98–1.16). The model of studies conducted in China and Japan had the weakest SRRE (1.01, 95% CI: 0.92–1.12; Chen et al. and Khan et al. excluded). Interestingly, the summary associations were modified by publication date, with the SRREs becoming monotonically weaker over time. For example, meta-analysis of 8 studies published prior to the year 2000 resulted in an SRRE of 1.30 (95% CI: 1.06–1.59), while the SRRE for the studies published in the past 5 years was 1.09 (95% CI: 0.98–1.21)" (Alexander. 2015).
So, if sub-analysis using models that looked for the isolated effects of fresh red meat (from processed meat), adjusted for more relevant factors, analyzed women only, and were conducted in countries outside of the United States showed once again that the allegedly "deadly" association between "red meat" and cancer is in fact one between the bacon, burger and overall junkfood laden diet the average American still considers "food", what's the conclusion then? Right, it's the same conclusion researchers have drawn based on the 2007 World Cancer Research Fund Report:
"One of the 10 universal guidelines for healthy nutrition in a report of the World Cancer Research Fund released at the end of 2007 is to “limit intake of red meat and avoid processed meat”, as a result of the “convincing evidence” for an association with an increased risk of colorectal cancer development" (Demeyer. 2008). 
In addition Daniël Demeyer, Karl Honikel, and Stefaan De Smet rightly demand that the food industry takes steps to develop "improved processed meats using new ingredients" by omitting or lowering the use of nitrite and nitrate (a real problem for bacon and sausages), reducing the exuberant salt content and taking measures to inhibit the damaging nitros(yl)ation reactions by haem and nitrite/nitrate present in the digestive tract and of the ensuing carcinogenic effects.
Table 2: Relative risk (RR)* of colorectal cancer in relation to animal food cooking method | all number > 1.00 indicate an increased risk, all number < 1.00 indicate a decreased risk (Lee. 2005).
In the end, all the efforts of the industry will yet be in vain, if you keep buying high nitrite bacon, and deep frying previously benign fresh meats to turn them into colorectal and cancer promoting agents (Lee. 2009 | note: Stir-fried meats are not associated with increased cancer risk in the same study).
Red Meat & Breast Cancer: Dietary Protein Sources in Early Adulthood and Breast Cancer Incidence | 22% Risk Increase for Red Meat Eaters, Substituting Poultry Normalizes Risk | Read the full Story
Bottom line: As the authors of the meta-analysis rightly point out "the state of the epidemiologic science on red meat consumption and CRC is best described in terms of weak associations, heterogeneity, an inability to disentangle effects from other dietary and lifestyle factors, lack of a clear dose-response effect, and weakening evidence over time" (Alexander. 2015). Accoringly, instead of condemning all read meats, scientists would be well-advised to conduct proper epidemiologic studies investigating diet and health outcomes in which they accurately measure food intake, dietary pattern differences across populations, food definitions, outcome classifications, bias and confounding, multicollinearity, biological mechanisms, genetic variation in metabolizing enzymes, and differences in analytical metrics and statistical testing parameters.

Needless to say that the anti-meat lobby is not interested in doing studies like this. After all, even a closer analysis of the data of the existing evidence shows: Red meat is not the culprit. It's processed junk food and the problem is not going to be soleved by replacing pork sausages with disgustingly tasting, but exactly as unhealthy tofu or soy sausages | Comment on Facebook!
References:
  • Alexander, Dominik D., et al. "Red Meat and Colorectal Cancer: A Quantitative Update on the State of the Epidemiologic Science." Journal of the American College of Nutrition ahead-of-print (2015): 1-23.
  • Chen, Kun, et al. "Nested case-control study on the risk factors of colorectal cancer." World Journal of Gastroenterology 9.1 (2003): 99-103.
  • Demeyer, Daniël, Karl Honikel, and Stefaan De Smet. "The World Cancer Research Fund report 2007: A challenge for the meat processing industry." Meat science 80.4 (2008): 953-959.
  • Khan, M. M. H., et al. "Dietary habits and cancer mortality among middle aged and older Japanese living in hokkaido, Japan by cancer sites and sex." Asian Pacific Journal of Cancer Prevention 5.1 (2004): 58-65.
  • Lee, Sang-Ah, et al. "Animal origin foods and colorectal cancer risk: a report from the Shanghai Women's Health Study." Nutrition and cancer 61.2 (2009): 194-205.