Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Appetite

Background and Rationale Despite substantial advances in pharmacological treatments for obesity, a considerable proportion of individuals remain non-responsive or intolerant to current medications. This highlights the urgent need for novel, sustainable, and non-pharmacological interventions. Transcutaneous auricular vagus nerve stimulation (taVNS) is an emerging non-invasive electroceutical approach. It targets the vagal afferent pathway to modulate the brain-gut axis, potentially influencing appetite regulation through neurophysiological circuits related to satiety, reward, and interoceptive processing.

Study Protocol and Procedures This study employs a double-blind, sham-controlled, crossover design. Participants will complete two separate experimental visits, separated by a washout period of at least 24 hours to prevent carryover effects. The sequence of the active and sham conditions will be strictly counterbalanced across participants.

During each experimental session, participants will first undergo baseline assessments. Following baseline, the investigational wearable device will be applied to the participant's ear. For the active condition, stimulation will be targeted at the left cymba conchae. The device is programmed with specific technical parameters, including a frequency of 20 Hz, a 50% duty cycle, and an intensity of 1 mA. For the sham condition, the setup will be identical in appearance but will lack the therapeutic electrical dosage to maintain double-blinding for both the investigator and the participant.

The designated stimulation (active or sham) will be delivered continuously for exactly 30 minutes. Concurrently with the stimulation, participants will be presented with a standardized, ad libitum buffet-style test meal. Immediately following the 30-minute eating and stimulation session, participants will engage in a series of computerized cognitive-behavioral tasks and state-assessment surveys designed to capture neurocognitive responses to food cues and interoceptive awareness.

Inclusion criteria

• Female participants aged between 20 and 50 years
• Body Mass Index (BMI) of 20 or higher
• Individuals who are capable of understanding the study procedures and providing voluntary informed consent

Exclusion criteria

• Presence of implanted metallic or electronic medical devices (e.g., cardiac pacemaker, implantable cardioverter defibrillator (ICD), cardiac stent, deep brain stimulator, or cochlear implant), except for dental implants and artificial joints
• History of diagnosed psychiatric disorders or current use of psychiatric medications
• Moderate to severe depression symptoms, defined as a Patient Health Questionnaire-9 (PHQ-9) score of 10 or higher
• Use of medications or medical interventions that may induce weight changes within the past 3 months
• Active inflammatory or infectious lesions on the ear (e.g., otitis externa, auricular dermatitis, or active skin infection)
• Specific dietary habits or restrictions, such as being a vegan or vegetarian
• Known food allergies
• Currently pregnant or breastfeeding
• History of diagnosed diabetes or other endocrine metabolic diseases
• Any other medical condition, illness, or history that, in the investigator's judgment, would make it difficult for the participant to complete the study or complicate the interpretation of study results