This water loss leads to a considerable drop in blood pressure, so much so that it led critics of these diets, such as Philip White, author of a nutrition column in the The Journal of the American Medical Association, to worry publicly about the “low blood pressure resulting from…losses of…fluid, sodium, and other minerals.” Discussions of the treatment of obesity with very low-carbohydrate diets would address the need to retain some carbohydrates in the diet to maintain “fluid balance” and “avoid large shifts in weight due to changes in water balance.” By the early 1970s, researchers had demonstrated that the water-retaining effect of carbohydrates was due to the insulin secreted, which in turn induced the kidneys to reabsorb sodium rather than excrete it, and that insulin levels were indeed higher, on average, in hypertensives than in normal individuals. Finally, by the mid-1990s, diabetes textbooks, such as Joslin’s Diabetes Mellitus, contemplated the likelihood that chronically elevated levels of insulin were “the major pathogenetic defect initiating the hypertensive process” in patients with Type 2 diabetes. But such speculations rarely extended to the potential implications for the nondiabetic public.

There are several possible explanations for why this phenomenon rarely entered into the discussions of hypertension and heart disease. Those investigators concerned with the dangers of hypertension might simply have considered the obesity literature or even the diabetes literature of little significance to their research, other than the obvious observation that obese and diabetic patients tend to be hypertensive and vice versa. Another possibility is that by the 1960s hypertension and high cholesterol were two of the three major risk factors associated with premature coronary heart disease (the third was smoking), so it was difficult to imagine that eating carbohydrates might be beneficial for one risk factor, cholesterol, while being detrimental for another, blood pressure.