Certain thyroid hormones predict response to weight-loss diets
Higher baseline free triiodothyronine (T3) and free thyroxine (T4) may predict more weight loss, but not weight regain, among overweight and obese adults with normal thyroid function in a diet-induced weight-loss setting, a study has found.
The study included 569 overweight and obese individuals aged 30 to 70 years with normal thyroid function participating in the 2-year Prevention of Obesity Using Novel Dietary Strategies (POUNDS) LOST randomized clinical trial.
Changes in body weight and resting metabolic rate (RMR) were evaluated during the 2-year intervention. Thyroid hormones—such as free T3, free T4, total T3, total T4 and thyroid-stimulating hormone (TSH)—anthropometric measurements and biochemical parameters were measured at different time points: baseline, 6 and 24 months.
On average, body weight decreased by 6.6 kg during the first 6 months and subsequently increased by 2.7 kg over the remaining period from 6 to 24 months. A positive correlation between baseline free T3 and total T3 was observed. On the other hand, free T4 was inversely associated with baseline body weight, body mass index and RMR. Total T4 and TSH were not associated with the mentioned parameters.
Higher baseline levels of free T3 and free T4 were found to be significantly associated with a greater weight loss during the first 6 months (p<0.05) after multivariate adjustments including dietary intervention groups and baseline body weight.
Comparing extreme tertiles, the multivariate-adjusted weight loss was −3.87 vs −5.39 kg for free T3 (p=0.02 for trend) and −4.09 vs −5.88 kg for free T4 (p=0.004 for trend). The thyroid hormones were not predictive of weight regain in 6 to 24 months. A similar pattern of associations was also seen between baseline thyroid hormone levels and changes in RMR.
Furthermore, changes in free T3 and total T3 levels showed a positive association with changes in body weight, RMR, body fat mass, blood pressure, glucose, insulin, triglycerides and leptin at months 6 and 24 (p<0.05 for all).
The present data suggest euthyroid overweight and obese individuals with relatively higher free T3 and free T4 levels might benefit more from a diet intervention strategy for weight loss, researchers said.
Thyroid hormones regulate energy expenditure and are thus essential in body weight regulation. Given such, thyroid dysfunction (eg, hyperthyroidism and hypothyroidism) may lead to significant changes in body weight and RMR. [Physiol Rev 2014;94:355-82; Mol Cell Endocrinol 2010;316:165-71]