Thyroid hormones and changes in body weight and metabolic parameters in response to weight loss diets: the POUNDS LOST trial.
Level 3 - non-randomized controlled study
Secondary observational cohort analysis of biomarker associations within a randomized trial
PubMed 28138133 · doi:10.1038/ijo.2017.28
What was done
Researchers performed a secondary analysis of 569 overweight and obese adults aged 30–70 with normal thyroid function participating in the 2-year POUNDS LOST randomized clinical trial. Serum thyroid hormones (free T3, free T4, total T3, total T4, and TSH), resting metabolic rate (RMR), body weight, and metabolic markers were measured at baseline, 6 months, and 24 months to assess associations with diet-induced weight loss and subsequent regain.
What was found
Participants lost an average of 6.6 kg during the first 6 months and regained an average of 2.7 kg from 6 to 24 months. Higher baseline free T3 and free T4 significantly predicted greater weight loss at 6 months after multivariate adjustment. Comparing the lowest to highest tertiles, adjusted 6-month weight loss was -3.87 ± 0.9 kg versus -5.39 ± 0.9 kg for free T3 (P trend = 0.02) and -4.09 ± 0.9 kg versus -5.88 ± 0.9 kg for free T4 (P trend = 0.004). Baseline thyroid hormones did not predict weight regain between 6 and 24 months. Decreases in free T3 and total T3 during the trial correlated with reductions in weight, RMR, body fat mass, blood pressure, glucose, insulin, triglycerides, and leptin at 6 and 24 months (all P < 0.05).
Why it matters
These findings suggest that variation in thyroid hormone levels within the clinically normal range may influence individual responsiveness to caloric restriction and metabolic adaptation during weight loss.
Limits
The study is an observational analysis within an intervention trial, precluding causal conclusions. All participants had normal baseline thyroid function, limiting generalizability to clinical thyroid disorders, and adherence to specific dietary macronutrient allocations was not isolated in this abstract.
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