Thyroid Hormones May Help Predict Successful Weight Loss

As regulators of metabolism, thyroid hormones help explain why some individuals lose weight while others don't on any given weight-loss regime.

With Qi Sun, MD, ScD, and J. Michael Gonzalez-Campoy, MD, PhD

Which individuals will lose or will not lose weight on any given dietary plan has been mostly unknown, but findings from the Prevention of Obesity Using Novel Dietary Strategies (POUNDS) LOST trial demonstrated that certain thyroid hormones appear predictive of a person’s ability to lose weight, as published in the International Journal of Obesity.

For overweight and obese patients, including those with type 2 diabetes, clinicians now have an effective method of assessing which patients might be encouraged to consider dietary adjustments to reverse their excess body weight, while others may have more confirmation that bariatric surgery offers a better long-term outlook for weight loss.1

Results from this randomized clinical trial provide a strong indication that even in adults with normal thyroid function, these hormones play a role in body weight regulation and may help identify individuals more responsive to a dietary intervention aimed at promoting weight loss,1 according to lead investigator Qi Sun, MD, ScD, an assistant professor of nutrition at the Harvard University School of Public Health in Boston, Massachusetts.

Researchers found that higher baseline free triiodothyronine (T3) and free thyroxine (T4) levels predicted more weight loss among overweight and obese adults with normal thyroid function. Unfortunately, these hormones were unable to offer any clue as to whether these individuals would regain the lost weight, said Dr. Sun. 

Thyroid hormone levels may predict best diet for successful weight loss.

Linking Thyroid Hormones and Body Weight

 “Our study was among the first to investigate the role of thyroid hormones in weight change in a controlled clinical trial rather than an observational study,” Dr. Sun, MD, ScD, told EndocrineWeb.

Higher levels of baseline free T3 and free T4, but not TSH, had a significantly associated to greater weight loss at six and 24 months, induced by weight loss dietary plans. However, baseline TSH did not predict weight loss or weight regain. In addition, changes in free T3 and total T3 levels, but not free T4 and total T4 or TSH, were positively associated with changes in body weight and metabolic parameters, including RMR, blood pressure, triglycerides, and leptin.

“Knowing which factors can predict weight loss increases our understanding of the biology of [body weight regulation], as well as to identify high-risk patients early on who may need to consider other options, such as bariatric surgery,” Dr. Sun told EndocrineWeb.

“This is a very important analysis,” said J. Michael Gonzalez-Campoy, MD, PhD, medical director and Chief Executive Officer of the Minnesota Center for Obesity, Metabolism and Endocrinology in Eagan, Minnesota, told EndocrineWeb, “It validates that there is a role for thyroid hormones in addressing weight loss and weight maintenance.”

Thyroid Hormone Levels Associated with Metabolic Rate, Too

A similar pattern of associations was observed between baseline thyroid hormones and changes in resting metabolic rate (RMR). There was a significant association between higher baseline free T3 and free T4 levels and a greater decrease in RMR during the weight loss period, but not in the weight regain period, according to the authors.

“We wanted to explore whether any factors could explain why some people lost weight and some do not,” said Dr. Sun. Investigators looked at weight loss between baseline and six months, and weight change between six months and 24 months. The associations between baseline thyroid hormones and changes in body weight, RMR, and body composition at six months and at 24 months were examined using linear regression (weight assessment at only six months and 24 months were used).

At baseline, participants with diabetes treated with medications or with unstable cardiovascular disease, or those using medications that affected body weight or who had insufficient motivation were excluded. In addition, anyone with subclinical thyrotoxicosis or hyperthyroidism based on TSH level was excluded from the analysis.

Study Findings Viewed as Clinically Useful for Treatment

“The use of thyroid hormone supplementation has been considered in the past as an adjunct to weight loss. However, making people hyperthyroid has more of a risk than there is benefit; there may be cardiac arrhythmias, damage to skeletal muscle, bone mineral density loss, and anxiety,” Dr. Gonzalez-Campoy told EndocrineWeb.

“This paper opens the doors for us to consider thyroid hormone supplementation, to move an individual patient’s thyroid hormone level from the low end to the high end of normal as a safe adjunct in a weight loss program. It mandates that we treat subclinical hypothyroidism and hypothyroidism,” he concluded.

POUNDS LOST Trial Methodology

Participants in another 2-year randomized clinical trial2 were assessed for changes in body weight and resting metabolic rate (RMR) during the intervention period, which offered outcomes data for the POUNDS LOST protocol.

In this study, freeT3, free T4, total T3, total T4, and thyroid-stimulating hormone (TSH), as well as anthropometric measurements and biochemical parameters were assessed at baseline, six months, and 24 months.1

The mean age of the 569 participants was 51.6 (± 9.0) years, and their mean BMI was 32.6 (± 3.8). They lost an average of 6.6 kg during the first six months, and subsequently regained an average of 2.7 kg for the remaining 6-24-month period. There were no significant differences in weight loss among the four different diets studied in the POUNDS LOST trial.2

In this analysis,1 study participants provided fasting serum samples at baseline and six months, and 429 of those participants also provided blood samples at two years.

Continue Reading:
Bariatric Endocrinology: 2015 Update
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