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October 2, 2019

Is red meat really bad for you? A new study ignites a scientific food fight.

Daily Briefing

    Clinical guidelines published this week in the Annals of Internal Medicine triggered a wave of pushback over claims that there isn't convincing evidence that adults need to reduce their intake of processed and red meats to improve their health, countering prominent dietary guidelines that for years have warned consumers to eat less of those foods.

    Cheat sheets: Evidence-based medicine 101

    Key findings

    The new guidelines are based on five systematic reviews of randomized and observational trials involving about 54,000 people conducted by a panel of 14 researchers from seven countries. The researchers used the data to gauge the potential impact of eating three fewer servings of processed or red meat each week on cancer, cardiovascular disease, and mortality, as well as how people viewed red meat.

    The researchers found that the effects of cutting three servings of red meat resulted in seven fewer cancer-related deaths per 1,000 people. The researchers similarly said they found "very small absolute risk," or statistically insignificant differences, and weak evidence related to potential harms for many of the other outcomes measured.

    As such, the guidelines concluded that people do not need to cut back on their red meat consumption for health reasons.

    Bradley Johnston, an associate professor at Dalhousie University, who co-led the research review, said that the researchers' "bottom line recommendation ... is that for the majority of people, but not everyone, continuing their red and processed meat consumption is the best approach."

    Further while the guidelines counter recommendations to reduce red meat consumption, three of the report's 14 authors said they still support guidelines that call for reducing red and processed meat consumption.

    Study ignites prompt pushback

    The new guidelines counter those from leading organizations, such as the U.S. Department of Agriculture, and the World Health Organization, and were met with swift pushback.

    Before the study was published, a group of 13 prominent nutrition researchers—including one of the study's co-authors—urged Annals' Editor-in-Chief Christine Laine to preemptively retract the study, "pending further review." The letter said that low-certainty evidence "is in no way a logical or even rational basis to recommend."

    In addition, the American Cancer Society, American Heart Association, and the Harvard T.H. Chan School of Public Health have denounced the findings.

    Frank Hu, chair of Harvard's Department of Nutrition, took aim at the researchers' interpretation of the data, noting that the observed reductions in health risk that the study authors considered small "are not small from a public health point of view and could save hundreds and thousands of lives in the U.S." He added, "Few dietary or lifestyle changes or even a drug could have multiple health benefits on major causes of deaths."

    Study shines light on holes in nutrition research

    But the study also renewed the discussion on the validity of existing nutrition research, Vox reports. The researchers in the guidelines acknowledged that their recommendation was "weak" and made with "low-certainty evidence," but argued that existing nutritional recommendations also are based on poor science.

    John Ioannidis, a Stanford University meta-researches and a longtime critic of nutrition science who was not involved in the research, said of the guidelines, "These papers provide a nice counterbalance to the current norm in nutritional epidemiology where scientists with strong advocacy tend to overstate their findings and ask for major public health overhauls even though the evidence is weak."

    As Vox explains, a lot of nutritional guidelines have been based on a wide range of research, including animal studies, case-control studies, and observational studies, which are widely viewed as less rigorous than cohort studies or randomized control trials.

    But for the new guidelines, the researchers weeded out those lower-quality studies and examined a broad range of research. They also notably compared the health effects of processed and unprocessed red meat, Vox reports. This different approach to evaluating nutritional research is why their nutritional guidelines differed from existing recommendations, according to Vox

    In a separate editorial accompanying the study, Aaron Carroll and Tiffany Doherty, both of the University of Indiana, also took aim at the traditional approach to nutrition research and argue that it may be time for "a major overhaul of the methods for communicating nutritional data" to the public.

    They wrote of the findings, "This is sure to be controversial, but it is based on the most comprehensive review of the evidence to date. Because that review is inclusive, those who seek to dispute it will be hard pressed to find appropriate evidence with which to build an argument" (AP/Los Angeles Times, 9/30; Monaco, MedPage Today, 9/30; Kelland, Reuters, 9/30; Aubrey, "The Salt," NPR, 9/30; Kolata, New York Times, 9/30; Carroll, "The Upshot," New York Times, 10/1; Belluz, Vox, 10/1; Carroll/Doherty, Annals of Internal Medicine, 10/1).

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