Holy Cow! Reheating the debate on eating red meat
EBM Focus - Volume 14, Issue 22
Reference: Ann Intern Med 2019 Oct 1 early online
Nutritional guidelines that make recommendations for public health and policy may result in changes to school lunch programs, fast food menus, and public perception of ‘healthy’ and ‘unhealthy’ foods. Unprocessed red meat (mammalian meat) and processed meats (preserved meat such as sausage, ham, and hot dogs) have long been considered ‘unhealthy,’ and multiple organizations and public health guidelines recommend reducing consumption of these foods.
Most recently, the NutriRECS Consortium conducted four systematic reviews and meta-analyses examining the effect of meat consumption on cardiovascular events, cancer outcomes, and all-cause mortality. As the guideline authors set out to write recommendations for individuals rather than as part of a larger public health effort, they additionally conducted a systematic review of quantitative and qualitative trials about meat consumption preferences. Each review used GRADE methodology. Overall, many of the included studies were at moderate to high risk of bias, and the resulting findings were of low or very low certainty.
The systematic review of randomized trials included 12 trials in total, but only two provided data on all-cause mortality and cardiometabolic outcomes. The authors present the findings of just one of these two trials (the Women’s Health Initiative [WHI]). The WHI was designed to assess the impact of reduced dietary fat intake on cardiovascular outcomes in postmenopausal women, and did not analyze red meat consumption specifically. However, the low-fat group was advised to increase intake of fruits, vegetables, and grains, and after 3 years reported consuming a mean of 1.4 fewer servings of meat. The WHI found that reduced dietary fat consumption was not significantly associated with nonfatal myocardial infarction, coronary death, cardiovascular disease, stroke, or all-cause mortality. In the meta-analysis of cohort studies, reduced red meat intake was associated with a reduced risk of cardiovascular mortality (risk difference per 1000 persons = 4, very low certainty) while reduced processed meat intake was associated with reduced all-cause mortality (risk difference per 1000 persons = 9, low certainty). In a meta-analysis of studies examining dietary patterns, in which studies were considered at higher risk of bias, a diet consisting of less red meat was associated with reduced all-cause mortality (risk difference per 1000 persons = 15, very low certainty). Additionally, reduced red meat consumption was associated with reduced cancer-related mortality (risk difference per 1000 persons = 7, low certainty). The mixed-methods systematic review found that omnivores are highly attached to eating meat (low certainty) and have little willingness to change meat consumption (low certainty).
Fourteen panelists from both the public and private sectors developed guidelines for red and processed meat consumption from these systematic reviews. The guideline suggests continuing current consumption of red and processed meat for adults (weak recommendation, low certainty evidence). Although some news headlines sensationalized these recommendations and many red meat lovers rejoiced, the reality of this recommendation is that the evidence is too weak to justify a strong statement for or against meat consumption. In particular, small benefits seen in cohort studies are especially prone to the “healthy user” or “compliance effect” bias. This occurs when people who comply with medical advice, such as avoiding red meat, also engage in other healthy behaviors that may account for the differences in mortality outcomes. It is noteworthy that the panel included patient values in making their recommendations, but several panelists have since been reported to have conflicts of interest with the beef industry. Food preferences remain a deeply ingrained part of our culture—certainly something to consider when weighing low-quality evidence against the strength of taste buds.