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 ≃0%) 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 expenditure have favored a return to usual body weight. Weight gain induced more apparent insulin resistance in the obese than the never obese subjects, suggesting a threshold effect of total body fat on this phenomenon.