The Nature of the Regulation
of Energy Balance
JAMES O. HILL
This chapter begins with the assertion that there is a physiological system(s) within the body that to some extent regulates energy utilization. The strongest evidence is the relative stability of body weight within individuals over time. Granted, the population of the United States is slowly gaining weight, but for any individual, this still represents a very small error in overall energy balance regulation. Consider that an average adult might consume 1,000,000 kcal each year. If that same individual gains 1–2 pounds per year, the error in matching energy expenditure to energy intake is still less than 0.5%. This suggests an extraordinary degree of regulation of energy.
The fact that body weight is defended further suggests the existence of some regulatory process. Any dieter can attest to the difficulty in sustaining a reduction in body weight below the “usual” level, suggesting processes that oppose weight loss and maintenance of a reduced weight.
While the regulation of energy balance occurs, the process is not perfect. The gradual weight gain seen in most people over the adult years suggests that the regulatory system may not be sufficient to maintain a constant body weight under all circumstances. Furthermore, the system may not be symmetrical, with defense against body weight gain weaker than the defense against body weight loss (see Chapter 8).
What might a regulatory system look like and how might it function to match energy intake with energy expenditure? Many different models have been developed. My colleagues and I have suggested that the nature of energy balance regulation and the body