Thyroid hormones and changes in body weight and metabolic parameters in response to weight loss diets: the POUNDS LOST trial.

International journal of obesity (2005). 2017;41(6):878-886

Plain language summary

The role of thyroid hormones in diet-induced weight loss and subsequent weight regain is largely unknown. The aim of this study was to examine the associations between thyroid hormones and changes in body weight and resting metabolic rate (RMR) in adults on a calorie-restricted diet. Data analysis was conducted among 569 overweight and obese adults with normal thyroid function participating in the 2-year Prevention of Obesity Using Novel Dietary Strategies (POUNDS) LOST clinical trial. Participants were assigned to diets that represented a reduced caloric intake of 750 kcal/day from estimated energy needs. Changes in body weight and RMR were assessed during the 2-year intervention. Thyroid hormones (free triiodothyronine (T3), free thyroxine (T4), total T3, total T4 and thyroid-stimulating hormone (TSH)), anthropometric measurements and biochemical parameters were assessed at baseline, 6 months and 24 months. Participants lost an average of 6.6 kg of body weight during the first 6 months and subsequently regained an average of 2.7 kg of body weight over the remaining period from 6 to 24 months. Baseline free T3, total T3 and free T4 were associated with baseline body weight, body mass index and RMR. Total T4 and TSH were not associated with these parameters. Higher baseline free T3 and free T4 levels were significantly associated with a greater weight loss during the first 6 months. Thyroid hormones did not predict weight regain in 6-24 months. In addition, changes in free T3 and total T3 levels were positively associated with changes in body weight, RMR, body fat mass, blood pressure, glucose, insulin, triglycerides and leptin at 6 months and 24 months. The authors concluded that on a reduced-calorie diet, higher baseline free T3 and free T4 predicted more weight loss, but not weight regain among overweight and obese adults with normal thyroid function. These findings reveal a role of thyroid hormones in body weight regulation and may help identify individuals more responsive to weight loss diets.

Abstract

BACKGROUND The role of thyroid hormones in diet-induced weight loss and subsequent weight regain is largely unknown. OBJECTIVES To examine the associations between thyroid hormones and changes in body weight and resting metabolic rate (RMR) in a diet-induced weight loss setting. SUBJECTS/METHODS Data analysis was conducted among 569 overweight and obese participants aged 30-70 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 RMR were assessed during the 2-year intervention. Thyroid hormones (free triiodothyronine (T3), free thyroxine (T4), total T3, total T4 and thyroid-stimulating hormone (TSH)), anthropometric measurements and biochemical parameters were assessed at baseline, 6 months and 24 months. RESULTS Participants lost an average of 6.6 kg of body weight during the first 6 months and subsequently regained an average of 2.7 kg of body weight over the remaining period from 6 to 24 months. Baseline free T3 and total T3 were positively associated, whereas free T4 was inversely associated, with baseline body weight, body mass index and RMR. Total T4 and TSH were not associated with these parameters. Higher baseline free T3 and free T4 levels were 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±s.e. was -3.87±0.9 vs -5.39±0.9 kg for free T3 (Ptrend=0.02) and -4.09±0.9 vs -5.88±0.9 kg for free T4 (Ptrend=0.004). The thyroid hormones did not predict weight regain in 6-24 months. A similar pattern of associations was also observed between baseline thyroid hormones and changes in RMR. In addition, changes in free T3 and total T3 levels were positively associated with changes in body weight, RMR, body fat mass, blood pressure, glucose, insulin, triglycerides and leptin at 6 months and 24 months (all P<0.05). CONCLUSIONS In this diet-induced weight loss setting, higher baseline free T3 and free T4 predicted more weight loss, but not weight regain among overweight and obese adults with normal thyroid function. These findings reveal a novel role of thyroid hormones in body weight regulation and may help identify individuals more responsive to weight loss diets.

Lifestyle medicine

Fundamental Clinical Imbalances : Hormonal
Patient Centred Factors : Mediators/Thyroid hormones
Environmental Inputs : Diet
Personal Lifestyle Factors : Nutrition
Functional Laboratory Testing : Blood
Bioactive Substances : TSH ; T3 ; T4

Methodological quality

Allocation concealment : Not applicable

Metadata

Nutrition Evidence keywords : Thyroid ; Obesity ; Weight ; T4 ; T3 ; TSH ; Resting metabolic rate