BACKGROUND
It is well known that thyroid hormone regulates some aspects of our metabolism. When thyroid levels are high (hyperthyroidism), our metabolism increases, we burn more calories and tend to lose weight. When thyroid levels are low (hypothyroidism), our metabolism slows down, we burn less calories and tend to gain weight. Once thyroid hormone levels return to normal after treating these 2 conditions, metabolism returns to normal.

One of the ways to measure metabolism is to look at the energy our body spends at rest. This is called resting energy expenditure. A previous small study has suggested that the resting energy expenditure is lower in patients with hypothyroidism even if they are treated with levothyroxine and their thyroid hormone levels are in the normal range. This study was done to determine the resting energy expenditure in a group of obese women with hypothyroidism attending a bariatric clinic

THE FULL ARTICLE TITLE
Muraca E et al 2020 Resting Energy Expenditure in Obese Women with Primary Hypothyroidism and Appropriate Levothyroxine Replacement Therapy. J Clin Endocrinol Metab. Apr 1;105.

SUMMARY OF THE STUDY
This study enrolled 649 obese women (body mass index (BMI) >30 kg/m2) attending a bariatric surgery clinic in Monza, Italy. Of these women, 564 (average age 44) had no history of thyroid problems, while 85 had a past history of hypothyroidism and were currently treated with levothyroxine (average age 49).

Both groups had serum TSH levels within the laboratory reference range (0.4-4.0 mU/L). Resting energy expenditure was measured and eating behavior and physical activity were assessed by questionnaires during a single visit to the clinic.

The hypothyroid group on levothyroxine had slightly higher levels of physical activity and lower levels of insulin resistance. The resting energy expenditure was 6% lower in this group compared to the group without hypothyroidsm. There was no correlation between resting energy expenditure and TSH levels in either group. There were no differences between the two groups in body mass index (BMI).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Obese hypothyroid women with normal TSH levels have slightly but significantly lower REE than obese women who were not hypothyroid. Even though the energy expenditure was lower in the group that had hypothyroidism and were treated with levothyroxine, their BMI was unaffected as compared to the group without hypothyroidism. While interesting, more studies are needed before changing current recommendations for weight management in patients with hypothyroidism.

— Vibhavasu Sharma, MD, FACE

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