Findings of Luvizotto et al. [13] suggest that physiologic levels of thyroid hormone are necessary for appropriate leptin expression and this dose of T3 could be used safely in the treatment of obesity because, at this level, T3 increases the expression of leptin, a hormone with central actions that cause a reduced food intake and an increase in energy expenditure, but does not decrease body protein. This evidence concerns the gene TG and obesity due to melanocortin 4 receptor deficiency.