Studies on the health impact of consuming red meat and processed meat are pervasive in nutritional science these days, with much evidence linking over-consumption to cardiovascular disease, obesity and cancer. So why do new guidelines now say there is no need to cut back? Our expert scientific contributor, Heather Huntsman, Ph.D., CSCS, weighs in on these recommendations and nuances in research that go beyond the headlines.
Last month, five reviews were published in the Annals of Internal Medicine to examine evidence on red meat and processed meat consumption and its impact on health outcomes, most notably cancer mortality, cancer risk, diabetes, and heart disease.1,2,3,4,5 The reviews conclude that adults can consume red and process meats at current levels of intake, despite overwhelming evidence from various studies that associate intake with incidence of adverse health conditions.
Inconsistent advice around recommendations on consumption often come from single studies in the nutrition, whereas the new reviews analyze data from dozens of studies involving millions of participants. However, that is what makes their recommendations somewhat unexpected and confusing.
Over the last five years, red meat, in particular processed meat, has been considered a carcinogen by organizations such as the World Health Organization and the World Cancer Research Fund International. When considering the saturated fat content of these particular types of meat, we have been told that the increased risk of cardiovascular disease is even stronger.
So, how could this panel of scientists recommend “…that adults continue current unprocessed red meat consumption (weak recommendation, low-certainty evidence). Similarly, the panel suggests adults continue current processed meat consumption (weak recommendation, low-certainty evidence).?” Does this mean red meat is not associated with an increased risk of cancer, cardiometabolic and cardiovascular disease? Is red meat safer to consume than we originally thought?
To answer that question, an understanding of nuances in nutritional research must be met. Although the gold standard in research is to conduct randomized controlled trials that try to limit the number of confounding variables (variables that may influence the measured outcome, but in a poorly understood and hard to calculate manner), these types of studies are extremely expensive, unrealistic, and often unethical in nutrition science. (Imagine keeping people in a lab and forcing them to only eat a highly controlled diet for 5 years. I’m not sure you’d get a lot of volunteers for that study!)
For this reason, much of the evidence we have to inform our nutrition recommendations is based on self-reported, questionnaire data, which run the risk of inconsistencies. This doesn’t mean that the data are invalid, only that they come with limitations. These limitations can mean a high number of confounding variables which automatically weakens any assumptions on direct associations between the variables of interest – in this case, red and/or processed meat and the health outcomes.
With this in mind, it is no surprise that the evidence linking red/processed meat and health will have a level of uncertainty. In the case of the Harvard study, the group of scientists chose to interpret their findings as inconclusive: there is not enough evidence to absolutely recommend people eliminate red and processed meat from their diet.
My interpretation as a scientist is that there may be some evidence linking consumption of certain types of meat to increased adverse health outcomes. Yes, cancer and cardiovascular disease are complex diseases that have a number of contributing factors to their incidence and progression apart from nutrition, such as exercise, pollutants, and genetics. Of those factors, nutrition and exercise are in our control. So, if there is any evidence at all, I personally will err on the side of caution and eliminate, or at least minimize, my own red and processed meats to lower my risk for certain diseases.
References:
- Zeraatkar D, et al. (2019) Red and Processed Meat Consumption and Risk for All-Cause Mortality and Cardiometabolic Outcomes: A Systematic Review and Meta-analysis of Cohort Studies. Ann Intern Med. doi: 10.7326/M19-0655. [Epub ahead of print]
- Han MA, et al. (2019) Reduction of Red and Processed Meat Intake and Cancer Mortality and Incidence: A Systematic Review and Meta-analysis of Cohort Studies. Ann Intern Med. doi: 10.7326/M19-0699. [Epub ahead of print]
- Vernooij RWM, et al. (2019) Patterns of Red and Processed Meat Consumption and Risk for Cardiometabolic and Cancer Outcomes: A Systematic Review and Meta-analysis of Cohort Studies. Ann Intern Med. doi: 10.7326/M19-1583. [Epub ahead of print]
- Valli C, et al. (2019) Health-Related Values and Preferences Regarding Meat Consumption: A Mixed-Methods Systematic Review. Ann Intern Med. doi: 10.7326/M19-1326. [Epub ahead of print]
- Zeraatkar D, et al. (2019) Effect of Lower Versus Higher Red Meat Intake on Cardiometabolic and Cancer Outcomes: A Systematic Review of Randomized Trials. Ann Intern Med. doi: 10.7326/M19-0622. [Epub ahead of print]
