Endocrine Abstracts

Objective: Because thyroid hormones positively regulate basal metabolic rate (BMR), one would expect that researchers systematically evaluate thyroid function in studies focused on BMR or resting energy expenditure (REE). The persent study aimed to document the percentage of human metabolic studies that find a difference in BMR/REE following an intervention and subsequently go on to evaluate whether thyroid function is altered.

Methods: A literature search was conducted in PubMed for human studies where BMR is measured by indirect calorimetry; the keywords “energy expenditure” or “metabolic rate,” and “indirect calorimetry” were utilized. There was no restriction on the publication date. Articles written in English with full-length text availability were reviewed. Studies were excluded if they were not human studies, if indirect calorimetry was not utilized to measure BMR, if there was no specific intervention, or if the results did not show an increase or decrease in BMR following the intervention. The full-text articles of selected studies were analyzed to determine if thyroid function was evaluated, and, if so, to contextualize the implications of the measurements.

Results: 3652 human studies that mentioned BMR or REE were identified. When the keyword “indirect calorimetry” was added, 671 articles were retained. Of the reviewed articles, roughly 50% identified a difference in BMR measured by indirect calorimetry following an intervention. Of those studies, less than 10% evaluated thyroid function. Those that did evaluate thyroid function were primarily assessing pharmacological interventions with thyroid hormones, including 3,5-diiodo-L-thyronine (T2) and levothyroxine (T4), or with growth hormone. Other studies evaluated thyroid function because their study populations comprised patients with hyperthyroidism.

Conclusions: Despite the crucial impact of thyroid hormones on BMR, the present study highlights a striking gap in research methodology. Among the reviewed studies observing changes in BMR following interventions, only a small minority proceeded to evaluate thyroid hormone levels. This oversight underscores the need for greater attention to thyroid function assessment in metabolic research, as it could offer valuable insights into the mechanisms underlying metabolic regulation and inform more targeted interventions for metabolic disorders. Thyroidologists should strive to raise awareness of the impact of thyroid hormones on BMR and to bridge the apparent gap with the metabolic research community.