PurposeIt is widely accepted that patients experience weight gain after total thyroidectomy, and preventive measures should be recommended.MethodsA prospective study was designed to assess the efficacy of a dietetic intervention to prevent post-thyroidectomy weight gain in patients undergoing surgery for both benign and malignant thyroid conditions. Patients undergoing total thyroidectomy were prospectively and randomly assigned to receive a personalized pre-surgery diet counseling (GROUP A) or no intervention (GROUP B), according to a 1:2 ratio. All patients underwent follow-up with body-weight measurement, thyroid function evaluation and lifestyle and eating habits assessment at baseline (T0), 45 days (T1) and 12 months (T2) post-surgery.ResultsThe final study group encompassed 30 patients in Group A and 58 patients in Group B. The two groups were similar in terms of age, sex, pre-surgery BMI, thyroid function and underlying thyroid condition. The evaluation of body weight variations showed that patients in Group A did not experience significant body weight changes at either T1 (p= 0.127) nor T2 (p= 0.890). At difference, patients in Group B underwent a significant body weight increase from T0 to both T1 (p= 0.009) and T2 (p= 0.009). TSH levels were similar in the two groups, both at T1 and T2. Lifestyle and eating habits questionnaires failed to register any significant difference between the two groups, apart from an increase in sweetened beverages consumption in Group B.ConclusionsA dietician counseling is effective in preventing the post-thyroidectomy weight gain. Further studies in larger series of patients with a longer follow-up appear worthwhile.