Until the salt hypothesis began receiving serious attention in the 1960s, the investigators paid little attention to nutritional explanations for the rise in blood pressure that accompanied Western diets and lifestyles. Instead, they debated whether it was the stress and tension of what they considered civilized life that led blood pressure to rise, as Donnison believed. Once the salt hypothesis raised the possibility that diet was responsible, investigators began to perceive the presence or absence of hypertension in isolated populations purely as a test of the salt hypothesis. Since hypertension only appeared in these populations when they gained access to Western diets, which frequently included salt-rich processed foods, the investigators saw their studies as confirming the salt hypothesis. By the 1990s, the absence of hypertension in isolated populations eating their traditional diets was still the most compelling evidence in support of the hypothesis.

Of course, the same societies that ate little or no salt ate little or no sugar and white flour, so the evidence supported both hypotheses, although the investigators were interested in only one. The notion that the refined-carbohydrate hypothesis could explain many of the other chronic changes in health among these populations was rarely discussed. In two cases—Gerald Shaper’s studies of nomadic tribes in Kenya and Uganda, and Ian Prior’s studies of South Pacific Islanders—the investigators first implicated refined carbohydrates as a possible cause of the emergence of hypertension in their populations, because sugar and flour constituted the conspicuous additions to the diet with Western influence. Then they embraced salt as the culprit, after they became aware that investigators in the U.S. believed salt to be the problem. In the early 1970s, when the Harvard hypertension specialist Lot Page and his colleagues set out to study “the antecedents of cardiovascular disease” in the Solomon Islands, they, too, considered their research to be solely a test of the salt hypothesis, so salt was the only aspect of the Solomon Islanders’ diet that they assessed. In what came to be considered a seminal study in the field, they concluded naturally enough that suspicion of the cause of high blood pressure among the islanders “falls most heavily on salt intake.”