Background: Obesity and hypothyroidism are both common disorders within the general population; Studies of thyroid function after diet-induced weight loss in patients with obesity have yielded conflicting results. The aim of the study was to prospectively evaluate the effect of diet plan on weight, body composition and thyroid function in patients with hypothyroid and obesity.

 Patient and method:  Serum levels of thyroid-stimulating hormone (TSH), total thyroxine (T4), and total triiodothyronine (T3) in hypothyroid patients with obesity were analyzed before and at the end of a 3-month weight loss program. Relationships between body weight or composition and changes in thyroid function were also investigated. Each study participant acted as his/her own control.