"Epistemic Certainty Surrounding Dietary Recommendations for Meat"
Ellen M. StreetEllen Street is a Ph.D. student in Nutrition at Oregon State University. Her graduate research is
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ResultsAmong the selected articles, I found a disparate ratio of hedges to boosters. True to Hyland’s explanation about the popular use of hedging in academic writing, directives, present indicative, and ambiguity take place of markers indicating certainty, such as boosters. However, in my analysis, I will focus primarily on the significance of the presence or absence of hedges and boosters to indicate epistemic modality. Dietary Guidelines for Americans 2015-2020 Overall trends in the 2015-2020 DGA indicate a lack of certainty, evident by the prevalent use of hedging and lack of boosters (see appendix table 3). The guidelines are phrased as suggestions without emphasis or authority. The suggestions rest on the possibility of lean meat as part of a healthy diet, save for one directive in Chapter 2 written for teen boys and men, calling for the necessity of reducing protein foods, without directly naming red meat: “Some individuals, especially teen boys and adult men, also need to reduce overall intake of protein foods...by decreasing intakes of meats, poultry, and eggs and increasing amounts of vegetables or other under consumed food groups.” Verbs indicating low and medium degrees of modality include the use of can, for lean meats, and may for processed meats. These markers suggest possible benefits of consuming red meat: “... can contribute important nutrients,” most often followed by the phrase “... within limits.” The most commonly used phrase, as long as, indicates the suggestions preceding it are contingent upon the reader’s current eating pattern: “... intake of these products [processed meats] can be accommodated as long as sodium, saturated fats, added sugars, and total calories are within limits in the resulting eating pattern …” The phrase, within limits, is also used to indicate restrictions on consumption of red and processed meats based on the current individual eating pattern. Interestingly, the section titled “The Science Behind Healthy Eating Patterns,” names “lower intakes of meats, including processed meats; processed poultry …” as identifiable characteristics of a healthy eating pattern. These characteristics are followed with a reference to the “About Meats and Poultry” section, which claims lean meats “can” be part of a healthy eating pattern. “The Science Behind Healthy Eating Patterns” also references a discussion in Chapter 2, about the excessive meat intake among men and adolescent boys in the United States. The only booster included in the DGA is strong, used to describe the strength of “evidence from mostly prospective cohort studies” and “randomized controlled trials,” indicating that red meat, processed meats, and poultry “are associated with reduced risk of CVD in adults.” There is no source listed for this statement. Compared to the section describing red meat intake for the broader audience, this statement expresses a stronger stance towards limiting red meat consumption, solely for populations of teen boys and men. However, there is no substantiation provided for either recommendation. AHA – “Recommended Dietary Pattern to Achieve Adherence to the American Heart Association/American College of Cardiology (AHA/ACC) Guidelines: A Scientific Statement From the American Heart Association” The AHA is a charity organization focused primarily on public health education, research, and professional training. The AHA Recommended Dietary Pattern to Achieve Adherence to the AHA/ACC Guidelines presents evidence-based strategies to help readers change dietary and lifestyle behaviors to prevent or reduce risk factors for cardiovascular disease, in accordance with the AHA/ACC guidelines. These recommendations outline diet practices and plans to cultivate a heart-healthy lifestyle for at-risk individuals with high LDL-C and BP. The dietary pattern guidelines state that individuals “should consume a dietary pattern that emphasizes vegetables, fruits, and whole grains; includes low-fat dairy products, poultry, fish, legumes, nontropical vegetable oils, and nuts; and has limited intake of sweets, SSBs [sugar sweetened beverages], red meats, and processed foods” (Van Horn et. al., 2016). The AHA/ACC do not use hedges to describe red meat and trans-saturated fat intake (see appendix table 4). Rather than boosters, the use of the directives limit and reduce indicate necessity whereas should, a deontic modal verb, expresses duty or obligation. American Institute for Cancer Research – “Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective – Recommendations for Cancer Prevention” The second expert report, or the Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective – Recommendations for Cancer Prevention, published jointly by the AICR/WCRF, outlines dietary and lifestyle guidelines for preventing cancer as recommended by a panel of world-renowned experts from a variety of disciplines. The language used in the section on red and processed meats displays strong epistemic certainty and the use of boosters (see appendix table 5). The introduction at the beginning of the meat section states, “The strongest evidence, corresponding to judgments of ‘convincing’ and ‘probable’, shows that red meat and processed meat are causes of colorectal cancer.” At the end of the section covering processed meats, the concluding statement expresses a lower modality: “There is strong evidence for plausible mechanisms operating in humans. Processed meat is a convincing cause of colorectal cancer.” The modality differs between processed and red meats considered separately, as well in the section on unprocessed red meat: "The general mechanisms through which red meat could plausibly cause cancer are outlined below." Could plausibly was used to describe the relation of general mechanisms to multiple types of cancer and red meat while the connection between processed meat to cancers other than colorectal uses the marker probable. One low modality marker appears often in statements regarding the relation of red processed and unprocessed meats to five different types of cancer: “Red or processed meats are convincing or probable causes of some cancers.” The overall trend in epistemic certainty is supported by boosters and directives such as convincing, limit, and avoid. Hedges are used to describe the link between red and processed meats with other types of cancer besides colorectal, using low modality markers (“…general mechanisms through which red meat could plausibly cause cancer are outlined below") and claiming processed meats are a "probable cause of stomach cancer." From the AICR/WCRF report, evidence clearly supporting the link between processed meat consumption and colorectal cancer is judged as strongly reliable, indicated by the prevalence of boosters. Recommendations to decrease consumption of processed meats are substantiated by boosters and directives to communicate certainty and authority. The Lancet Oncology – “Carcinogenicity of consumption of red and processed meat” The Lancet Oncology monograph shows a distinct difference in epistemic certainty describing red and processed meat. Statements regarding red meat consumption and its link to cancer use hedges while statements linking processed meat to colorectal cancer show epistemic certainty (see appendix table 6). Hedges include this example: “The Working Group classified consumption of red meat as probably carcinogenic to humans”; booster use includes mention of strong evidence connecting red meat to colorectal cancer and many positive associations between the two. An interesting ambiguity was found between neighboring statements specifying red and processed meats: “The Working Group classified consumption of red meat as probably carcinogenic to humans,” preceded by the assertion that "Overall, the Working Group classified consumption of processed meat as “carcinogenic to humans.” Unprocessed red meat is classified in the Lancet Oncology monograph as “probably carcinogenic to humans,” considering “substantial” data showing positive associations between red meat and colorectal, prostate and pancreatic cancer and “strong mechanistic evidence” (Beland, 2015). Archives of Internal Medicine – “Red Meat Consumption and Mortality” An Archives of Internal Medicine article, written by Pan et al., investigated associations between processed and unprocessed red meat consumption and mortality over the period of “2.96 million person-years of follow-up,” between two large cohorts. The discussion of the study results primarily indicate probability, but do not make any certain claims until the last sentence of the comments (discussion) section. This article includes hedges and low modality markers to describe the connection between red meat and cancer (see appendix table 7). The article placed agency and causality on individual components within processed meats. High sodium content in processed meats “may increase CVD risk.” Secondary products of nitrites (added preservatives) are “potential carcinogens.” Dietary heme iron, sourced from red meat, is “positively associated with myocardial infarction and fatal coronary heart disease.” The following sentences from the last two paragraphs link unprocessed and processed red meats to cancer: “... we found that greater consumption of unprocessed and processed red meats is associated with higher mortality risk” and “… red meat intake has been associated with increased risks of colorectal cancer and several other cancers.” The selected excerpts use the indicative present to portray a strong stance and express factuality. The final sentence “indicate[s]” red meat replacements “may lower” risk of death due to red meat consumption. American Journal of Epidemiology – “Red meat and processed meat consumption and all-cause mortality: A meta-analysis” The meta-analysis of 13 studies, published in the American Journal of Epidemiology, links the consumption of unprocessed and processed red meats as well as total meat consumption with all-cause mortality. The findings discussed in the concluding discussion section reflect epistemic certainty in statements associating high consumption of processed meat to all-cause mortality and colorectal cancer: “Among cancer types, colorectal cancer has been most consistently associated with red meat and processed meat consumption.” In the AICR/WCRF report, red and processed meats are also linked to esophageal, lung, pancreatic, endometrium, stomach and prostate cancers. But the evidence is described by the AICR/WCRF as limited, or merely suggestive for these associations. There are no known cancer associations linked to consumption of lean meats, poultry or fish, save for Cantonese-style salted fish (associated with nasopharyngeal cancer, supported by probable evidence). However, red and processed meats are linked to colorectal cancer with convincing and probable evidence, as reflected in the AJE meta-analysis, published seven years after the publication of the AICR/WCRF second expert report. Also, “In conclusion, findings from this meta-analysis showed a positive association between the consumption of red meat, particularly processed meat, and all-cause mortality.” The italicized markers were classified as boosters (see appendix table 8), due to their extra emphasis linking processed meats and all-cause mortality among the 13 analyzed studies. Other statements are hedged with the low modality marker, may: “Red meat and processed meat consumption may increase all-cause mortality by increasing the risk of major chronic diseases, including cardiovascular disease and cancer.” The authors back their associations with possible mechanisms by which red and processed meats may contribute to major chronic disease development, citing the World Cancer Research Fund and addressing the individual components in red processed meats that may contribute to carcinogenicity and all-cause mortality. |