Figure 1.

This figure, modified from the work of Jean Mayer and colleagues, illustrates the hypothesis that energy balance may be easier to achieve at high energy throughput (ie. high energy expenditure). We illustrate the concept to a threshold for physical activity, above which people are in the regulated zone of energy balance and below which they are in the unregulated zone. In the regulated zone energy intake is “pulled along” to meet high energy needs, and energy intake and expenditure are very sensitive to changes in each other. At low energy throughput, energy intake and expenditure are only weakly sensitive to changes in each other and maintaining a healthy body weight requires sustained food restriction.