“Meat Consumption and Health: Food for Thought”, 2019-11-19 (; backlinks; similar):
For some time, medical and science organizations have been beating the drum that red and processed meat are bad for you. For almost as long, they have lamented that their efforts to inform the public have not convinced enough people to change their consumption. This month’s issue offers us food for thought on why. The field of nutritional epidemiology is plagued by observational studies that have conducted inappropriate analyses, accompanied by likely erroneous conclusions (1). Many studies selectively report results, and many lack an a priori hypothesis. Many use notoriously unreliable self-reports of food consumption while failing to collect or appropriately control for data on numerous potential confounders.
…Four more studies join the evidence base this month, and because they review all of the evidence that came before, they cannot be accused of cherry-picking. The first was a meta-analysis of cohort studies that focused on how dietary patterns, including differing amounts of red or processed meat, affected all-cause mortality, cardiometabolic outcomes, and cancer incidence and mortality (6). More than 100 studies including more than 6 million participants were analyzed. The overall conclusions were that dietary patterns, including differences in meat consumption, may result in only small differences in risk outcomes over long periods.
The next study was a meta-analysis that homed in specifically on cohort studies examining how reductions in red and processed meat might affect cancer incidence and mortality (7). It included 118 studies with more than 6 million participants, and it, too, found that the possible impact of reduced meat intake was very small. The third study was a meta-analysis of cohort studies that looked specifically at meat consumption and its relationship to all-cause mortality and cardiometabolic outcomes (8), and—once again—it found that any link was very small.
…In a fourth analysis in this issue (9), researchers examined randomized controlled trials that compared diets with differing amounts of red meat consumption for at least 6 months. They found 12 eligible studies, but one of them—the Women’s Health Initiative—was so large (almost 49,000 women) that it dominated the analysis. We can wish for more studies, and we could hope that they had more homogenous outcomes and better fidelity to assigned diets, but the overall conclusions from what they had were that “red meat may have little or no effect on major cardiometabolic outcomes and cancer mortality and incidence.”
…it may be time to stop producing observational research in this area. These meta-analyses include millions of participants. Further research involving much smaller cohorts has limited value. High-quality randomized controlled trials are welcome, but only if they’re designed to tell us things we don’t already know.