Metabolic Effects of Exercise
in Overweight Individuals
WIM H. M. SARIS
It is appealing to postulate that exercise may be a key factor in weight control (see Chapter 93). A convincing argument for this regulatory role is the observation that with the exception of sumo wrestlers (who need high body mass for physical combat), the prevalence of obesity is almost zero for athletes. Those who leave sports frequently increase in body weight and fatness. More difficult to prove is the role of inactivity in the etiology of obesity. Furthermore, the public view is that exercise is ineffective for weight control because the amount of exercise required to change weight is too great to be practical, and that the increase in energy raises appetite, thus negating the effect of the additional exercise.
Exercise is linked to power output and heat production, and thus with energy expenditure. According to the laws of thermodynamics, obesity is a result of a positive energy balance in which energy intake has exceeded expenditure over a prolonged period. It is not clear which part of the equation is mostly affected in obesity. There are many factors associated with energy intake, expenditure, and their interaction.
The difference in physical activity between normal and overweight individuals has been examined in a plethora of studies but data are not conclusive. Most studies find no relation between inactivity and obesity, but are severely hampered by methodological problems and unclear definitions of physical activity. A case linking decreased activity with body weight regulation can be made only indirectly with indicators of a sedentary lifestyle, such as cars per household, hours per week watching television, or level of work.
Reduced activity may be balanced partly by the increased energy cost of weight-bearing activities. Moving around with a higher body mass implies a higher energy cost. This was demonstrated in a weight loss study in which each experimental subject wore a vest with weights compensating for his or her weight loss. Subjects’ decrease in energy expen-