This single-center, randomized, single-blind, sham-controlled pilot study aims to evaluate the adjunctive effect of transcutaneous auricular vagus nerve stimulation (taVNS) in overweight/obese patients who show a poor weight loss response to lifestyle intervention. Participants who achieve no more than 5% weight loss after 12 weeks of lifestyle intervention will be randomized to receive either taVNS plus lifestyle intervention or sham stimulation plus lifestyle intervention for an additional 12 weeks. The primary objective is to compare the percent change in body weight from baseline between the two groups after 12 weeks of intervention. Secondary objectives include evaluation of changes in body composition and fat distribution, autonomic function, liver-related parameters, and glycemic and lipid-related metabolic parameters.

Obesity is a chronic metabolic disease with substantial health consequences, and lifestyle intervention remains the foundation of weight management. However, a considerable proportion of overweight or obese individuals fail to achieve clinically meaningful weight loss after structured lifestyle intervention. In this study, patients with poor response to lifestyle intervention are defined as those who have completed 12 weeks of lifestyle intervention with weight loss of 5% or less.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a noninvasive neuromodulation technique that stimulates the auricular branch of the vagus nerve and may improve autonomic balance, appetite regulation, and energy metabolism. This study is designed to investigate whether taVNS can enhance weight loss and improve metabolic outcomes when used as an adjunct to lifestyle intervention in overweight/obese patients with poor early response.

A total of 24 participants will be enrolled at a single center and randomized in a 1:1 ratio to either the taVNS plus lifestyle intervention group or the sham stimulation plus lifestyle intervention group. The intervention period will last 12 weeks. All participants will receive standardized lifestyle guidance including dietary management and exercise management. Dietary intervention will be individualized based on basal metabolic rate measured by InBody and guided by the Dietary Guidelines for Chinese Residents, with an intended daily energy deficit of approximately 500 kcal. Exercise management will require at least 3 days of moderate-to-high intensity physical activity per week, with a total duration of at least 150 minutes, monitored by a wearable device.

Participants in the active treatment group will receive taVNS applied to the left cymba conchae using an intermittent electrical stimulation pattern (15 seconds on, 5 seconds off), frequency of 20 Hz, pulse width of 0.2 ms, and intensity gradually increased to a tolerable mild tingling sensation, usually 1.0-2.5 mA. Stimulation will be administered twice daily for 30 minutes each time, 5 times per week, for 12 weeks. Participants in the control group will receive sham stimulation at the left tail of the helix, with the same stimulation schedule and device settings.

Assessments will be performed at baseline and after 12 weeks of intervention, including anthropometric measurements, body composition analysis, autonomic function testing, laboratory testing, and evaluation of hepatic steatosis and fibrosis using FibroTouch and liver MRI. The primary endpoint is percent change in body weight from baseline at week 12. Secondary endpoints include changes in body composition and fat distribution, autonomic function, liver-related parameters, and glycemic and lipid-related metabolic parameters.

Inclusion Criteria:

1. Completed 12 weeks of lifestyle intervention treatment with ≤5% weight loss during the treatment period;
2. Completed 12 weeks of lifestyle intervention, with less than 1 month since completion, and achieved ≤5% weight loss during the intervention period;
3. Current body mass index (BMI) ≥28 kg/m², or BMI ≥24 kg/m² with at least one weight-related comorbidity (e.g., hypertension or fatty liver disease);
4. Willingness to provide written informed consent.

Exclusion Criteria:

1. Presence of diseases that may substantially affect body weight homeostasis, including Cushing's syndrome, uncontrolled thyroid disease (thyroid-stimulating hormone >6.0 mIU/L or <0.4 mIU/L), malignancy, or similar conditions;
2. Use within the past 3 months of medications that may significantly affect body weight, including glucocorticoids and antipsychotic agents;
3. Skin infection or damage involving the auricular area;
4. Women planning pregnancy in the near future;
5. Inability to complete the 12-week intervention period for practical reasons, such as frequent business travel or planned travel.

Only participants are masked in this trial. Participants are randomly assigned to active taVNS plus lifestyle intervention or sham stimulation plus lifestyle intervention. To maintain masking, sham stimulation uses the same device, similar stimulation procedures, and the same treatment schedule as active stimulation, but is applied to a non-vagal auricular site (the left tail of the helix). Randomization codes are generated by an independent unblinded team and allocation is concealed using sealed, opaque envelopes. Emergency unblinding materials are prepared and securely retained.