Effects of levothyroxine substitution therapy on hunger and food intake in individuals with hypothyroidism.

In individuals with hypothyroidism and overweight, levothyroxine substitution therapy is often expected to cause weight loss due to its effect on resting energy expenditure. However, despite levothyroxine-induced enhancement of resting energy expenditure, fat mass loss is rarely seen after levothyroxine substitution therapy. The mechanism behind this conundrum is unknown. The aim of the study was to assess the effect of levothyroxine therapy on hunger sensations and ad libitum food intake in individuals with hypothyroidism. Prospective cohort study of 18 newly diagnosed hypothyroid women (thyroid-stimulating hormone (TSH) >10 mU/L). Participants were investigated at diagnosis, after normalization of TSH (<4.0 mU/L), and after 6 months of successful treatment. Eighteen age and body mass index-matched healthy controls were also included. Hypothyroid individuals were treated with levothyroxine according to European Thyroid Association guidelines. Changes in hunger sensation were assessed using visual analog scales (cm) before and during a standardized mixed meal test, and food intake was measured during a subsequent ad libitum meal (g). After 6 months of levothyroxine therapy, mean resting energy expenditure was increased by 144 kcal/day (10%) (P < 0.001). Weight loss was comprised of 0.8 kg fat-free mass while fat mass remained unchanged. Fasting hunger sensation increased from a mean of 4.5 (s.d. 2.2) cm to 5.5 (s.d. 2.2) cm (P = 0.047). The numerical increase in ad libitum meal intake did not reach statistical significance. Our data suggest that levothyroxine-induced hunger may be a culprit in the lack of fat mass loss from levothyroxine therapy.