Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Appetite

Seoul National University Hospital60 enrolled

Overview

This study tests a new way to help control appetite. Researchers will use a wearable device on the ear. This device sends gentle electrical pulses to a nerve. This is called vagus nerve stimulation. The main goals of this study are: * To see if this device helps people eat less. * To check if it lowers feelings of hunger. * To measure how it changes responses to food cues. Healthy adult women will join this study. Each person will have two study visits. At one visit, the device will be turned on. At the other visit, the device will be off. This is a fake or "sham" treatment. During each visit, researchers will: * Give a standard meal for 30 minutes. * Measure how much food each person eats. * Ask questions about hunger and fullness. * Use computer tasks to check food cravings. This study may find a safe, medicine-free way to manage eating habits.

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.

Interventions

Transcutaneous Auricular Vagus Nerve Stimulation (taVNS)DEVICE

A single 30-minute session of active taVNS (20 Hz, 1 mA, 50% duty cycle) will be administered to the left cymba conchae. As this is a crossover study, each participant receives this intervention once during their assigned active period.

Sham StimulationDEVICE

A single 30-minute session of sham stimulation will be administered at the same location (left cymba conchae). The device is applied for 30 minutes with the same visual and tactile setup, but no effective electrical stimulation is delivered. This is performed once during the participant's assigned sham period.

Eligibility

Sex: FEMALEMin age: 20 YearsMax age: 50 YearsHealthy volunteers:

Medical Language ↔ Plain English

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

Outcomes

Primary Outcomes

Difference in Food Intake

The amount of food consumed during an ad libitum buffet meal (standardized Gimbap). It is calculated as the difference in the weight of food (grams) consumed between the active taVNS session and the sham stimulation session.

Time frame: During the 30-minute ad libitum meal session in each experimental visit

Secondary Outcomes

custom-developed Interoceptive State Appetite Scale (VAS-100)

Subjective states of hunger, fullness, and desire to eat are assessed using the 15-item Interoceptive State Appetite Scale (VAS-100). Each of the 15 items is evaluated on a 0 to 100 scale, where higher scores indicate greater intensity of the felt state. All 15 items share the identical unit of measure (VAS score, 0-100) and will not be aggregated into a composite score. Instead, the individual score for each of the 15 items will be reported separately to evaluate their independent changes.

Time frame: Baseline (pre-stimulation) and immediately after the 30-minute stimulation/meal session.

Eating-Related Interoceptive Awareness

This measure assesses the participant's ability to perceive and respond to internal bodily signals related to hunger, satiety, and food intake control using a 7-item questionnaire. Six items are rated on a 5-point Likert scale (1-5), and one item is rated on a 6-point Likert scale (1-6). The individual score for each of the 7 items will be analyzed and reported separately.

Time frame: Immediately after the ad libitum buffet meal and the final VAS-100 appetite assessment in each experimental session.

Attentional Bias Toward Food Stimuli

Attentional bias measured via a Dot-probe task. It is calculated based on the difference in reaction times (ms) between dots replacing food images versus neutral images.

Time frame: Immediately after the 30-minute stimulation/meal session.

Inhibitory Control Toward Food Cues: False Alarm Rate

Performance on a Go/No-Go task to measure response inhibition toward food-related stimuli. The specific indicator is the False Alarm Rate, defined as the proportion of incorrect responses during No-Go trials. To evaluate the intervention effect, the difference in False Alarm Rates between the active stimulation session and the sham session will be calculated and analyzed using a paired t-test.

Time frame: Immediately after dot probe task

Inhibitory Control Toward Food Cues: d-prime

Performance on a Go/No-Go task to measure signal detection sensitivity and response inhibition toward food-related stimuli. The specific indicator is the $d'$ (d-prime) index, calculated based on the standardized hit rates and false alarm rates. To evaluate the intervention effect, the difference in $d'$ values between the active stimulation session and the sham session will be calculated and analyzed using a paired t-test.

Time frame: Immediately after the Dot-probe task