Diabetes, obesity, coronary heart disease, gallstones and gall-bladder disease, and cavities and periodontal disease are intimately linked. As early as 1929, physicians were reporting that a fourth of their coronary-heart-disease patients also had diabetes. Diabetics, as Joslin noted, were especially prone to atherosclerosis, which became increasingly clear after the discovery of insulin. Studies in the late 1940s revealed that diabetic men were twice as likely to die of heart disease as nondiabetics; diabetic women were three times more likely. Moreover, diabetics had an exceptionally high rate of gallstones; and the obese had an exceptionally high rate of gall-bladder disease. As Joslin’s textbook also observed, “The destruction of teeth and the supporting structures is very active just prior to the onset of diabetes,” connecting cavities to the disease.

Cleave’s desire for simplicity led him to theorize that any cluster of diseases so intimately associated must have a single underlying cause. Darwin’s theory of evolution led Cleave to believe that endemic chronic disease must be caused by a relatively rapid change in our environment to which we had not yet adapted. He called this idea “The Law of Adaptation”: species require “an adequate period of time for adaptation to take place to any unnatural (i.e., new) feature in the environment,” he wrote, “so that any danger in the feature should be assessed by how long it has been there.” The refining of carbohydrates represented the most dramatic change in human nutrition since the introduction of agriculture. “Whereas cooking has been going on in the human race for probably 200,000 years,” Cleave said, “there is no question yet of our being adapted to the concentration of carbohydrates…. Such processes have been in existence little more than a century for the ordinary man and from an evolutionary point of view this counts as nothing at all.”

Cleave believed the concentration of carbohydrates in the refining process did its damage in three ways.

First, it led to overconsumption, because of what he called the deception of the appetite-control apparatus by the density of the carbohydrates. He contrasted the “eating of a small quantity of sugar, say roughly a teaspoonful,” with the same quantity in its original form—a single apple, for instance. “A person can take down teaspoonfuls of sugar fast enough, whether in tea or any other vehicle, but he will soon slow up on the equivalent number of apples…. The argument can be extended to contrasting the 5 oz. of sugar consumed, on the average, per head per day in [the United Kingdom] with up to a score of average-sized apples…. Who would consume that quantity daily of the natural food? Or if he did, what else would he be eating?”

Second, this would be exacerbated by the removal of protein from the original product. Cleave believed (incorrectly) that peptic ulcers were caused by the lack of protein necessary to buffer the gastric acid in the stomach.