Many controlled studies have measured the cardiovascular effects of replacing animal ("saturated") fats with seed oils (predominantly the omega-6 polyunsaturated fat linoleic acid) in humans. A number of these studies recorded heart attacks and total mortality during the following 1-8 years. Several investigators have done meta-analyses (literature reviews) to try to tease out overall conclusions from these studies.
I'm pleased to point out a new meta-analysis of these controlled trials by Dr. Christopher Ramsden and colleagues (1). This paper finally cleans up the mess that previous meta-analyses have made of the diet-heart literature. One recent paper in particular by Dr. Dariush Mozaffarian and colleagues concluded that overall, the controlled trials show that replacing animal fat with linoleic acid (LA)-rich seed oils reduces heart attack risk (2). I disagreed strongly with their conclusion because I felt their methods were faulty (3).
Dr. Ramsden and colleagues pointed out several fundamental flaws in the review paper by Dr. Mozaffarian and colleagues, as well as in the prevailing interpretation of these studies in the scientific literature in general. These overlap with the concerns that I voiced in my post (4):
Omission of unfavorable studies, including the Rose corn oil trial and the Sydney diet-heart trial.Inclusion of weak trials with major confounding variables, such as the Finnish mental hospital trial.Failure to distinguish between omega-6 and omega-3 fatty acids.Failure to acknowledge that seed oils often replaced large quantities of industrial trans fats in addition to animal fat in these trials.
Dr. Ramsden and colleagues accounted for all of these factors in their analysis, which has never been done before. They chose inclusion criteria
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