This is where physiological psychologists provided a viable alternative hypothesis to explain both hunger and weight regulation. In effect, they rediscovered the science of how fat metabolism is regulated, but did it from an entirely different perspective, and followed the implications through to the sensations of hunger and satiety. Their hypothesis explained the relative stability of body weight, which has always been one of the outstanding paradoxes in the study of weight regulation, and even why body weight would be expected to move upward with age, or even move upward on average in a population, as the obesity epidemic suggests has been the case lately. And this hypothesis has profound implications, both clinical and theoretical, yet few investigators in the field of human obesity are even aware that it exists.

This is yet another example of how the specialization of modern research can work against scientific progress. In this case, endocrinologists studying the role of hormones in obesity, and physiological psychologists studying eating behavior, worked with the same animal models and did similar experiments, yet they published in different journals, attended different conferences, and thus had little awareness of each other’s work and results. Perhaps more important, neither discipline had any influence on the community of physicians, nutritionists, and psychologists concerned with the medical problem of human obesity. When physiological psychologists published articles that were relevant to the clinical treatment of obesity, they would elicit so little attention, said UCLA’s Donald Novin, whose research suggested that the insulin response to carbohydrates was a driving force in both hunger and obesity, that it seemed as though they had simply tossed the articles into a “black hole.”

The discipline of physiological psychology was founded on Claude Bernard’s notion of the stability of the internal environment and Walter Cannon’s homeostasis. Its most famous practitioner was the Russian Ivan Pavlov, whose career began in the late nineteenth century. The underlying assumption of this research is that behavior is a fundamental mechanism through which we maintain homeostasis, and in some cases—energy balance in particular—it is the primary mechanism. From the mid-1920s through the 1940s, the central figure in the field was Curt Richter of Johns Hopkins. “In human beings and animals, the effort to maintain a constant internal environment or homeostasis constitutes one of the most universal and powerful of all behavior urges or drives,” Richter wrote.