Energy expenditure, fat oxidation, and body weight regulation: A study of metabolic adaptation to long-term weight change

Relatively low rates of energy expenditure and fat oxidation predict body w eight gain. Weight gain, in turn, is associated with increases in energy ex penditure and fat oxidation that may oppose further weight change. In respo nse to experimental weight gain induced by overfeeding, increases in energy expenditure and fat oxidation are overcompensatory, i.e. greater than pred icted for the change in body composition. To determine whether such metabol ic adaptation occurs in response to spontaneous long term weight change, we conducted a longitudinal study in which 24-h energy expenditure (24-EE) an d 24-h respiratory quotient (24-RQ; i.e. fat to carbohydrate oxidation) wer e repeatedly measured in 102 Pima Indians at baseline and after a mean foll ow-up of 3.6 +/- 2.7 yr, during which changes in body weight varied widely (-21 to +28 kg). We found that changes in 24-EE and 24-RQ in response to we ight change were related to the amount of weight change, even after adjustm ent for body composition (partial r = 0.23 and -0.30, respectively; both P < 0.05). For a 15-kg weight gain, the increases in 24-EE (+244 Gal/day) and 24-h fat oxidation (+152 Gal/day) were 33 and 53 Gal/day greater than pred icted from the cross-sectional relationship between both measures and body weight. Changes in 24-EE and 24-RQ varied substantially among individuals. Thus, on the average, spontaneous long term weight changes are accompanied by small metabolic adaptations in both energy expenditure and fat oxidation . The metabolic responses to weight changes are highly variable among indiv iduals, however.