BALANCING ENERGY-EXPENDITURE AND BODY-WEIGHT

It has been nearly 50 y since Mayer and coworkers hypothesized that th e mechanisms controlling energy balance are accurate in persons with h igh levels of physical activity, but that in sedentary persons there i s a threshold of physical activity below which these mechanisms become imprecise and that this leads to obesity. This hypothesis, however, w as relatively untested in humans because of the difficulty of measurin g total energy expenditure (TEE). The development of the doubly labele d water method has obviated this problem and we have now begun to test the Mayer hypothesis in humans. A review of cross-sectional data from doubly labeled water studies in adults provided support for the Mayer hypothesis in men but not in women. Men with TEE >approximate to 1.75 times the resting metabolic rate (RMR) had lower body mass indexes th an did those with lower expenditures. Further support for the hypothes is was obtained from a longitudinal study of previously obese women. W omen with ratios of TEE to RMR >approximate to 1.75 gained less weight than did those with lower energy expenditures. When a subset of the l ess active women was placed in an exercise program that increased TEE: RMR to approximate to 1.75, weight gain was arrested. Weight gain resu med when the exercise program ended. The doubly labeled water method n ow makes it possible to quantitatively and objectively test a hypothes is proposed almost 50 y ago. Results generally support the Mayer hypot hesis of a threshold of physical activity that protects against weight gain.