Prescription Thyroid Replacement Does Not Affect Outcomes in an Intensive Weight Reduction Program

With the complex role of the thyroid in metabolism and conflicting evidence of weight gain or loss as a result of prescription thyroid hormone replacement (THR), it is important to understand how THR affects weight loss beyond the standard measures of body weight % and body mass index (BMI). We examined differences in body composition improvement in individuals taking and not taking THR over 60 d of an intensive weight loss program. The 20Lighter Program (T20LP), a doctor-supervised weight loss and metabolic health program, included 6 wk of patent-pending very low calorie meal plans and a 3-wk customized transition back to a normal dietary intake. Of 2200 participants completing T20LP by December 31, 2017, ~10% reported taking prescription THR. From initial baseline to 60 d, T20LP participants from both groups showed statistically significant and clinically meaningful reductions in body weight, BMI, % body fat, visceral fat, metabolic age, and increases in % body water. To our knowledge, our study is the first large-scale analysis comparing weight loss outcomes in participants who take THR and participants who do not. Our data show both groups do equally well with respect to % body weight lost, BMI reduction, body fat and visceral fat reduction, and improvement in tissue hydration, and we found no disadvantage in any physiologic or metabolic outcome in weight loss participants on THR. Weight loss participants requiring prescription THR are capable of achieving body composition and metabolic improvements on par with those who do not require prescription THR.