Misuse of Meta-analysis in #Nutrition Research | Nutrition | JAMA | The JAMA Network
▻http://jamanetwork.com/journals/jama/fullarticle/2654401
A 2014 meta-analysis examined the relationship between saturated fat intake and coronary artery disease.2 One of the included prospective studies, the Oxford Vegetarian Study,3 included vegans, ovolacto vegetarians, fish eaters, and meat eaters, with reported saturated fat intake ranging from 6% to 7% of energy in vegan participants to approximately twice that amount in the other diet groups. Those in the highest tertile of saturated fat intake had nearly triple the risk of fatal ischemic heart disease compared with the lowest tertile.
In contrast, another study included in the meta-analysis, the Malmö Diet and Cancer cohort study,4 had no groups at the lower end of saturated fat intake, which ranged from 13% to more than 22% for the lowest to the highest quintiles, and no significant association between saturated fat intake and risk of cardiovascular events was detected. The Malmö authors cautioned, “only 1.2 percent of the present study population actually followed national Swedish recommendations (less than 10 energy percent) on saturated fat intake. Strictly speaking, the SFA-CVD [saturated fatty acids-cardiovascular disease] hypothesis is thus not fully testable in this population.”
Nevertheless, the Malmö study was given substantial weight in the meta-analysis, which concluded that available evidence did not support limiting saturated fat, a conclusion repeated in a New York Times commentary proclaiming “Butter is Back” and a Time magazine cover displaying an artistic butter swirl and the bold headline “Eat Butter,” and cited by the 2015 Dietary Guidelines Advisory Committee. The following year, a Gallup poll registered a sharp decline in the number of US adults limiting fat in their diets.