Table 1 Inclusion and exclusion criteria

Inclusion criteria

• Adults of either sex, aged between 20 and 50 years

•   25 ≤ BMI < 35 kg/m² at screening

• Stable weight for at least 12 weeks prior to screening

Exclusion criteria

• Women who are pregnant, breastfeeding, trying to become pregnant, or not using adequate contraception

• Women in perimenopause, menopause, or postmenopause or who have had early menopause (under 40 years old) or a hysterectomy or oophorectomy

• A history of severe cranial trauma with changes in cranial anatomy or metallic intracranial implants

• Patients with preexisting irritations, cuts, or lesions where the tDCS electrodes would be placed

• Type 1 diabetes; metabolic or acute complications of diabetes within the past 6 months

• A history of any acute or chronic intestinal disease (e.g., Crohn’s disease, inflammatory bowel disease)

• Having received nutritional counseling in the last 6 months by a nutritionist

• A history of severe depression or other serious psychiatric comorbidities

• A history of gastric bypass, antrectomy, or small bowel resection

• A history of chronic pancreatitis or idiopathic acute pancreatitis

• Myocardial infarction, coronary artery bypass surgery, posttransplant cardiomyopathy, or stroke in the last 6 months

• Any abnormality in clinical laboratory tests that might prevent safe participation in the study

• Diagnosed and/or treated tumor (except basal cell skin cancer, carcinoma in situ of the cervix, or prostate cancer in situ) in the last 5 years

• A history of known hemoglobinopathy or chronic anemia

• Blood donation of 1 U or more (≥ 500 ml) or significant blood loss (≥ 500 ml) in the last 2 weeks, or blood transfusion in the past 8 weeks

• Oral antidiabetic drug treatment and/or herbal preparations or nonprescribed medications that could affect glycemic control in the last 12 weeks

• Chronic oral or parenteral corticosteroid treatment (> 7 consecutive days) in the last 4 weeks

• Weight loss treatment agents (e.g., orlistat, sibutramine, topiramate, bupropion) in the last 12 weeks

• Ingestion of mineral oil or fiber supplements (e.g., Benefiber [GSK, Philadelphia, PA, USA], Metamucil [Procter & Gamble, Cincinnati, OH, USA])

• Unstable doses of lipid-lowering drugs in the past 8 weeks

• Unstable doses of thyroid hormone replacement in the past 12 weeks

• Enrolled in another drug/device trial

• Any laboratory abnormalities identified in screening, such as alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) more than three times the upper limit of normal, glomerular filtration rate estimated by the CKD-EPI equation ≤ 30 ml/min/1.73 m², TSH outside the normal range, or triglycerides ≥ 400 mg/dl.

• A history of active substance abuse (including alcohol) within the past year.

• Any acute condition or exacerbation of a chronic condition that would, in the investigator‘s opinion, interfere with the procedures