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.

What is the BASE-DIET Study? The BASE-DIET study is a clinical trial looking at how a healthy diet and lifestyle program can help people newly diagnosed with Graves' disease (an autoimmune thyroid condition) manage weight changes and improve their health during and after treatment.

Graves' disease often causes weight loss when it's active. But after treatment, many people gain back the weight-and sometimes even more than they had before. This study wants to find out if a personalized diet and lifestyle approach can help prevent that excessive weight gain and promote better health outcomes.

Why is this study important? When thyroid function is brought back to normal (called "euthyroidism"), many patients regain weight. In fact, up to 80% of patients report weight gain after treatment, which can impact self-esteem and health.

Some research shows this weight gain might go beyond what people weighed before getting sick. This study wants to see whether a structured diet and lifestyle program can make a positive difference compared to the usual medical care alone.

Who is participating in the study?

Adults newly diagnosed with Graves' disease at endocrinology clinics in Italy are invited to take part. Participants must:

• Be over 18 years old
• Have been diagnosed within the previous month
• Have a BMI between 16 and 35
• Be willing to commit to a 1-year program They cannot participate if they are pregnant, have certain health conditions, or are already taking weight-related medications.

How is the study organized?

The study randomly assigns people to one of two groups:

1. Intervention Group (ILI) - This group receives:

   • Personalized nutrition counseling by a licensed dietitian
   • A Mediterranean-style, low-calorie diet plan
   • Support on physical activity and lifestyle
   • Follow-up appointments at 3, 6, 9, and 12 months

2. Control Group (UMC) - This group receives:

   • Standard medical care for Graves' disease
   • General lifestyle and diet tips (no personalized plan)
   • Two check-ins at the beginning and end of the 12-month period What is being measured? The main goal (primary outcome) is to see if people in the intervention group are less likely to gain more than 1 kg over their pre-disease weight after 12 months.

Secondary goals include:

• Changes in Body Mass Index (BMI)
• Body composition (muscle vs. fat mass)
• Waist-to-hip ratio
• Adherence to a Mediterranean diet
• Improved eating habits and quality of life What happens during follow-up?

At each check-up, researchers will:

• Measure weight, height, waist and hip size
• Use a body composition test (bioimpedance analysis)
• Review a 3-day food diary
• Ask about physical activity and lifestyle changes
• Check how closely participants follow the prescribed diet Only the intervention group receives repeated, in-depth dietary coaching. How long does the study last? The full study duration for each participant is 12 months, with an extended follow-up period for data collection.

How many people are in the study? The study plans to enroll 60 people (30 in each group), which accounts for a small number of possible dropouts.

Is the study safe and ethical?

Yes. It follows strict ethical guidelines:

• All participants give written informed consent
• Privacy is fully protected
• Participation is voluntary, and people can leave at any time There are no outside sponsors-it's a non-profit, academic study led by IRCCS Maugeri in Pavia, Italy.

What will happen with the results?

Results will be:

• Published in scientific journals
• Shared at medical conferences
• Made available to the public The goal is to better understand how diet can help people with Graves' disease manage their weight and improve their recovery.

Inclusion Criteria

• Diagnosis of Graves' disease in an endocrinology setting based on the presence of thyrotoxicosis and positive TRAb antibodies.
• Diagnosis of Graves' disease within 1 month prior to randomization.
• BMI > 16 kg/m² and < 35 kg/m² at the time of the first visit for Graves' disease.
• Age > 18 years.
• Ability to commit to the duration of the study.
• Ability to provide informed consent and willingness to participate in the study.

Exclusion Criteria

• Relapse of Graves' disease or thyrotoxicosis not related to Graves' disease.
• Any serious cardiovascular or renal event in the last 6 months.
• Current pregnancy, breastfeeding, or planning pregnancy during the study period.
• Any condition potentially leading to fluid overload such as heart failure (NYHA class > I) or liver cirrhosis.
• Previously diagnosed significant psychiatric disorder (e.g., schizophrenia, post-traumatic stress disorder, obsessive-compulsive disorder).
• Active eating disorder.
• Uncontrolled depression.
• Uncontrolled epilepsy.
• Known cause of malabsorption (including uncontrolled celiac disease, lactose intolerance, or inflammatory bowel disease).
• Ongoing therapy with weight-modifying medications (e.g., GLP-1 analogs, metformin).
• Estimated BMI before disease onset < 18 kg/m². This parameter will be calculated based on the "estimated pre-disease body weight" as reported by the patient.