The effect of time-restricted eating accompanied by weight loss on thyroid function in adults with type 2 diabetes

Abstract Context Time-restricted eating (TRE) is a lifestyle intervention associated with beneficial cardiometabolic effects. The impact of TRE-induced weight reduction on thyroid hormonal responses is not well elucidated. Objective To evaluate the effects of TRE accompanied by weight loss on thyroid function in adults with obesity and type 2 diabetes (T2DM). Methods We performed an exploratory analysis of a randomized, crossover, open label study in adults with obesity and T2DM who underwent two dietary interventions: TRE and standard lifestyle. Each intervention period had 6-weeks. Thyroid function was assessed by TSH, free T4 (fT4), free T3 (fT3), and reverse T3 (rT3). Results Thirty-nine participants without known thyroid disease (age 56.3 years, 35.9% male, BMI 32.4 ± 5.7 kg/m2) were included. TRE induced significant weight loss (-2.93kg) compared to the standard lifestyle period (0.59kg) [mean differences between intervention periods of -3.50 kg ± 2.9] (p < 0.001). Despite this robust weight-lowering effect, there was no significant differences in TSH (0.49 mUI/L ± 3.0 p = 0.32), fT3(-0.57 pmol/l ± 2.7 p = 0.19), fT4 (fT4 -0.55 pmol/l ± 3.8 p = 0.38) and rT3 (-0.94 ng/dL± 5.9 p = 0.350) between intervention periods. Reinforcing these findings, there was no treatment effect interaction on any thyroid function test evaluated. In addition, there was no significant change in the fT3: fT4 and fT3:rT3 ratios between treatment interventions. Conclusion Despite inducing significant weight loss, TRE did not exert a significant effect on thyroid function in individuals with obesity and early T2DM.