The goal of this clinical trial is to determine whether a structured dietary-nutritional intervention can prevent excessive weight regain and improve body composition and lifestyle habits in adults recently diagnosed with Graves' disease (Basedow's disease). The main questions it aims to answer are: * Can a dietary intervention prevent patients from regaining more than 1 kg above their pre-disease body weight after restoring euthyroidism? * Does the intervention lead to improvements in body composition, dietary habits, and adherence to the Mediterranean diet? Researchers will compare patients receiving an Intensive Lifestyle Intervention (ILI) including a personalized diet and lifestyle counseling to patients receiving Usual Medical Care (UMC) with general lifestyle advice to see if the dietary intervention results in less weight regain and better metabolic and anthropometric outcomes. Participants will: * Receive antithyroid medication as standard medical care. * Be randomized into either the intervention group (ILI) or control group (UMC). If in the ILI group, participants will: * Receive an individual nutritional consultation within 1 week of enrollment. * Follow a personalized Mediterranean-style low-energy diet. * Attend follow-up visits at 3, 6, 9, and 12 months for: * Dietary adherence and lifestyle assessments. * Anthropometric measurements (weight, BMI, waist/hip circumference). * Bioimpedance analysis (at 6 and 12 months) for body composition. * Dietary intake logs and adherence assessments (3-day food diary). If in the UMC group, participants will: * Receive routine clinical management for Graves' disease. * Complete basic dietary and lifestyle questionnaires at baseline and 12 months. * Undergo anthropometric measurements and bioimpedance at T0 and at the end of study. This study aims to provide evidence on the role of nutritional support in managing weight and metabolic risks in patients undergoing treatment for Graves' disease.