In one of his recent Health Care Triage videos, Aaron Carroll calls attention to a recent study published in the Journal of the American Heart Association that supposedly tells us something new about plant-based diets and health.
In this study, cardiovascular and all-cause mortality were the primary outcomes measured, and the authors found that participants with the highest adherence to the overall plant-based diet and pro-vegetarian diet had an associated decrease in risk of cardiovascular disease (16%), cardiovascular disease mortality (31-32%), and all-cause mortality (18-25%).
At first glance, the results of a plant-based diet seem promising, but Dr. Carroll points out a major issue with the study; the people who are more likely to adhere to plant based diet are also more likely to exhibit more overall healthy behaviors, like increased likelihood of physical activity, and decreased likelihood of smoking or alcohol consumption. They’re also more likely to be wealthy, better educated, white, and female. These drivers of health work in combination to positively affect health outcomes.
It’s difficult (nearly impossible, even) to disentangle a single health behavior—diet—from a multitude of other factors that influence health. They’re interrelated and associated with other predictors for health, decreasing the utility of this research that’s supposed to be focused on diet. The big takeaway from Dr. Carroll is that these kinds of studies really aren’t that useful.
Observational studies in nutritional science don’t give us much new information (an overabundance of observational studies have shown similar associations between plant-based diets and positive health outcomes), and the information they do give us is questionable. Even the research we’ve believed for years that eating red meat is bad for our health is based on shaky evidence. As Dr. Carrol puts it bluntly, “We’ve outlived the utility of observational studies in nutritional epidemiology.” We don’t need more of those. What we need, is to put our resources toward randomized controlled trials, and better study designs that tell us something new.
Watch the whole Health Care Triage video here: