A third famous clinical trial that is cited again and again is the Finnish Mental Hospital study. I first heard about this study from a top nutrition expert who assured me that it was really “the best possible proof” that saturated fat is unhealthy.

In 1958, researchers seeking to compare a traditional diet high in animal fats to a new one high in polyunsaturated fats selected two mental hospitals near Helsinki. One they called Hospital K and the other, Hospital N. For the first six years of the trial, inmates at Hospital N were fed a diet very high in vegetable fat. Ordinary milk was replaced with an emulsion of soybean oil in skim milk, and butter was replaced by a special margarine high in polyunsaturated fats. The vegetable oil content of the special diet was six times higher than in a normal diet. Meanwhile, inmates of Hospital K ate their regular fare. Then the hospitals swapped, and for the next six years, Hospital K inmates got the special diet while Hospital N returned to their normal one.

In the special-diet group, serum cholesterol went down by 12 percent to 18 percent, and “heart disease was halved.” This is how the study is remembered and is the conclusion that the study directors, Matti Miettinen and Osmo Turpeinen, themselves drew. In a population of middle-aged men, they said, a diet low in saturated fats “exerted a substantial preventive effect upon coronary heart disease.”

But a closer look reveals a different picture. Heart disease incidence (which the investigators defined as deaths plus heart attacks) did go down dramatically for the men at Hospital N: there were sixteen such cases among men on the normal diet compared to only four on the special diet. But the difference found in Hospital K was not significant. Nor was any difference observed among the women. The biggest problem with the study, however, was that, like the subjects in the LA Veterans Trial, its population was a moving target. With admissions and discharges over the years, the composition of the groups changed by half. A shifting population means that an inmate in the group who died of a heart attack might have been admitted three days earlier and the death would have had nothing to do with his diet; and, vice versa, a patient who was released might have died soon thereafter but would not have been recorded in the study.

This and other design problems were so great that two high-level NIH officials together with a professor at George Washington University felt moved to criticize the study in a letter to The Lancet asserting that the authors’ conclusions were too statistically weak to be used as any kind of evidence for the diet-heart hypothesis. Miettinen and Turpeinen acknowledged that their study design was “not ideal,” including the fact that the study population was far from stable, but asserted in their defense that a perfect trial would be “so elaborate and costly . . . [that it] may perhaps never be performed.” Their imperfect trial, meanwhile, would have to stand: “we do not see any reason to change or modify our conclusions,” they wrote. The research community accepted this “good-enough” reasoning, and the Finnish Mental Hospital study earned a spot as one of the linchpins of evidence for the diet-heart hypothesis.

Nina Teicholz - Page 77