Body Weight Changes in Hyperthyroidism: Timing and Possible Explanations during a One Year Repeated Measurement Study

Area of Science:

• Endocrinology
• Metabolism
• Clinical Research

Background:

• Weight gain is a frequent, often undesirable, outcome for patients undergoing hyperthyroidism treatment.
• Understanding the dynamics of weight change during antithyroid drug (ATD) therapy is crucial for patient management.

Purpose of the Study:

• To investigate the timing of body weight changes within the first year of ATD treatment for hyperthyroidism.
• To assess the relationship between weight fluctuations and changes in thyroid hormones, resting energy expenditure (REE), physical activity, and energy efficiency.

Main Methods:

• A longitudinal study design tracking patients with new-onset hyperthyroidism every two months for one year.
• Measurements included body weight, thyroid hormone levels (free T3), REE, physical activity (steps), and exercise performance.

Main Results:

• Patients experienced significant weight gain (68.9 to 74.1 kg) over the year of ATD treatment.
• A significant decrease in REE (1,630 to 1,484 kcal/24 h) and changes in energy efficiency were observed.
• Individual weight changes correlated significantly with REE and free T3 levels, but not with physical activity levels.

Conclusions:

• Hyperthyroidism treatment led to a notable increase in body weight.
• The observed weight gain was primarily associated with a reduction in REE, with minimal correlation to energy efficiency and no correlation to physical activity levels.