Effects of changes in body weight on carbohydrate metabolism, catecholamine excretion, and thyroid function

Abstract

Background: Weight gain and loss increases and decreases energy expenditure, respectively, out of proportion to changes in metabolic mass. Objective: We hypothesized that changes in energy expenditure associated with weight gain or loss were due in part to changes in catecholamine release, thyroid hormones, carbohydrate utilization, or a combination thereof. Methods: Urinary catecholamine excretion, serum thyroid hormone concentrations, and results of 3-h oral-glucose-tolerance tests were examined in obese and never-obese subjects at their usual weights, during weight loss or gain, and at stable weights 10-20% below or 10% above usual. Results: Urinary norepinephrine excretion decreased significantly during and after weight loss and increased during and after weight gain. Serum concentrations of reverse triiodothyronine increased significantly during and after weight loss, whereas serum concentrations of triiodothyronine increased significantly (by Ϸ0%) during and after weight gain. Serum insulin and glucose concentrations during the oral-glucose-tolerance test increased significantly after weight gain in obese subjects. The percentage change in urinary norepinephrine excretion and in serum concentrations of triiodothyronine were significantly correlated with percentage changes in energy expenditure and with each other. Conclusions: Changes in body weight were associated with changes in catecholamine excretion and thyroid hormones, which might-by virtue of the effects on energy expenditurehave favored a return to usual body weight. Weight gain induced more apparent insulin resistance in the obese than the neverobese subjects, suggesting a threshold effect of total body fat on this phenomenon.Am J Clin Nutr 2000;71:1421-32. KEY WORDSObesity, diabetes, glucose, catecholamines, thyroid hormones, weight change, energy homeostasis, body weight, adults INTRODUCTIONMaintenance of weight gain or loss is associated with compensatory changes in energy expenditure that oppose the maintenance of a body weight that is different from the usual weight (1, 2). These changes may account, in part, for the poor long-term efficacy of obesity treatments (3). Catecholamine release in response to insulin-induced hypoglycemia is diminished in reduced-obese patients (4-9); serum triiodothyronine decreases in subjects during the process of weight loss and increases in subjects during dynamic weight gain (5, 6, 10-13). The decreased insulin sensitivity after weight gain and the beneficial effects of even modest amounts of weight reduction on carbohydrate metabolism and insulin sensitivity in some patients are well documented (14-18). Catecholamine-and thyroid hormone-mediated effects on energy expenditure and alterations in the efficiency of carbohydrate metabolism (ie, the fraction of energy from carbohydrate that is oxidized compared with the fraction that is stored) are possible mediators of changes in energy homeostasis associated with changes in body weight. We performed long-term metabolic studies of obese and never-obese hu...

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