Impact of Restrictive Diets on Inflammation and Quality of Life in Autoimmune Thyroiditis

The purpose of this clinical trial is to evaluate whether a dietary intervention can improve clinical and immunological outcomes in women with autoimmune thyroid disease (AITD), including Hashimoto's thyroiditis and Graves' disease. The study will enroll premenopausal women aged 18 to 55 years. The dietary intervention consists of the simultaneous exclusion of three groups of potentially pro-inflammatory dietary components: * Gluten-containing cereals, including wheat, barley, and rye. * Casein, the main protein found in milk and dairy products. * High-glycemic-index carbohydrates, such as refined sugar, white bread, and white rice. The primary objective is to determine whether the dietary intervention reduces serum levels of anti-thyroid peroxidase (anti-TPO) antibodies, which are markers of thyroid autoimmunity. Secondary objectives include evaluating whether the intervention improves: * Fatigue and energy levels. * Mood and emotional well-being. * Gastrointestinal symptoms. * Health-related quality of life. Women following the dietary intervention will be compared with women who continue their habitual diet to assess the effectiveness of the intervention. Group allocation will be based on participants' choice at study enrollment. Participants will: * Follow either the dietary intervention or their usual diet for 12 months while continuing their prescribed medical treatment. * Attend four study visits: at baseline and after 4, 8, and 12 months. * Undergo anthropometric assessments (body weight and waist circumference), blood sampling, stool collection, and a telemedicine consultation with a thyroid specialist at each visit. * Complete brief online questionnaires every month to assess dietary adherence, fatigue, mood, gastrointestinal symptoms, and quality of life.

Inclusion Criteria: * Women aged 18 to 55 years, of reproductive age and not menopausal * Confirmed diagnosis of autoimmune thyroiditis (Hashimoto's thyroiditis or Graves' disease) based on clinical, hormonal and immunological criteria * Under clinical follow-up by an endocrinology unit * Stable thyroid function; if on pharmacological treatment, stable for at least 3 months before study entry * No relevant nutritional deficiencies (vitamin D, selenium, zinc, iron or vitamin B12), or adequately supplemented according to clinical criteria * Willingness to participate in a supervised nutritional program and signed informed consent Exclusion Criteria: * Other active autoimmune or systemic diseases (e.g., lupus, multiple sclerosis, type 1 diabetes), active inflammatory bowel disease, peptic ulcer or intestinal infections * Established menopause or perimenopause * Body mass index outside the range 18.5-29.9 kg/m2 * Pregnancy or breastfeeding * Use of immunosuppressive drugs or corticosteroids * Previous restrictive diets * Severe food intolerances or conditions preventing adherence to the protocol (e.g., wheat allergy, celiac disease, casein allergy)