TG and obesity due to melanocortin 4 receptor deficiency: Although the association between bariatric surgery and thyroid function seems clear and mainly based upon thyroid autoimmunity, the mechanism of this relationship may be complex and bidirectional: some studies indicate a role for autoimmune subclinical hypothyroidism in the pathogenesis of obesity (111),, while others support the hypothesis that the excess of dysfunctional adipose tissue may be responsible for changes in serum thyroid hormone levels (90, 112).