Subjects were given meal tickets of a certain color, corresponding to a particular diet unknown to them. The control diet was 40% calories from fat, “mostly of animal origin,” and the experimental diet involved substitution of vegetable oils for 2/3 of the animal fat, incorporated into the diet in the form of milk, ice cream, margarine, and cheeses. In this trial the low saturated fat experimental diet produced a 13% reduction in serum cholesterol compared to the control group throughout the trial, objectively confirming the experimental group’s adherence to the low saturated fat diet.
After eight years of participation, there was no significant difference in heart disease rates, the primary endpoint, manifested as sudden cardiac death or heart attacks (78 events in 65 men in the control group vs. 60 events in 52 men in the experimental). However, when pooled with the data for cerebral infarction and "other secondary end points," the difference in total cardiovascular disease reached statistical significance, with 119 major events occurring in 96 subjects in the control group and 85 events in 66 subjects in the experimental group (p=0.01).
This clinical trial is all too often cited as supporting the diet-heart hypothesis. By reading the abstract, it seems reasonable, until you track down what these "secondary endpoints" happen to be. Which turned out to be quite difficult. After requesting an interlibrary loan from Pittsburgh, I eventually tracked down the ~80 page tome describing the study in vivid detail. And here are the secondary endpoints:
- ruptured aneurysms
- limb amputations due to peripheral vascular disease
- and “miscellaneous” events, such as occlusion of the mesenteric arteries
To say limb amputation and occlusion of arteries supplying your intestines is related to saturated fat intake would be a bit of a stretch. Extremity amputation was required if the dorsal pedal pulse and the posterior tibial pulse on the affected foot were absent or extremely faint.
Deaths due to non-atherosclerotic causes were higher in the experimental group (85 vs. 71 in control), resulting in near identical rates of total mortality (177 in control vs. 174 in experimental group). This study also raised an interesting question as to whether or not a diet high in unsaturated fat may contribute to death by other causes, since the experimental group had more non-cardiac deaths (specifically from cancer: 7 deaths in experimental, and 2 in control). However, these numbers are much too small to determine if this result was significant or not. Other such clinical trials have not supported this phenomenon.
This study is another perfect example of how profoundly misleading an abstract can be, and how important it is to read each study in its entirety before making bold claims that this study supports the idea that eating a low saturated fat diet prevents heart disease.
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