Transcutaneous Auricular Vagus Nerve Stimulation Combined With Lifestyle Intervention for Visceral Fat Reduction in Adults With Overweight or Obesity

Obesity is a major public health burden, and there is growing interest in neuromodulation approaches that may facilitate weight management beyond conventional lifestyle intervention. The vagus nerve plays a key role in the regulation of appetite, energy homeostasis and visceral function. Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that targets the auricular branch of the vagus nerve (ABVN) at the cymba conchae, and prior studies suggest it may aid weight reduction and metabolic improvement. The neural mechanisms underlying the effects of taVNS on visceral fat reduction remain unclear; thalamocortical circuitry and whole-brain functional network organization are plausible substrates linking vagal afferent input to eating behavior and energy regulation.

In this trial, 50 adults aged 18-49 years with overweight or obesity (BMI 24-32.5 kg/m2) and a habitual sedentary lifestyle will be recruited. After baseline evaluation, eligible participants will be randomly assigned in a 1:1 ratio to the taVNS group or the control group using a computer-generated block randomization sequence (fixed block size of 4, SPSS 26.0). All participants will follow the same standardized lifestyle program throughout the 4-week intervention period: a calorie-restricted diet (1,000-1,500 kcal/day; 55-60% carbohydrate, 25-30% fat, 20% protein) and aerobic exercise of at least 30 minutes per session, 3 times per week. Participants in the taVNS group will additionally self-administer taVNS using an electronic acupuncture stimulator (SDZ-II, Huatuo, Suzhou, China) in dense-disperse mode at 20 Hz; stimulation will be delivered to the cymba conchae of the left and right ears on alternating days at the maximum intensity tolerable without pain, twice daily (morning and afternoon), 30 minutes per session, 5 days per week for 4 consecutive weeks. All treatments are home-administered after standardized training, with real-time adherence monitoring through electronic diaries. Adverse events are recorded by participants in electronic diaries and reviewed weekly by study personnel.

Outcome assessors and data analysts are blinded to group allocation. Anthropometric and body-composition measures (height, weight, BMI, body fat percentage, visceral fat index by bioelectrical impedance analysis, BCA-2A, Tsinghua Tongfang, China) and resting-state fMRI (3.0-T scanner, Discovery MR750, GE Healthcare) are acquired at baseline (week 0) and post-intervention (week 4). The primary outcome is the change in visceral fat index (VFI) from baseline to week 4. Secondary outcomes include changes in body weight, BMI and body fat percentage; group-by-time changes in thalamocortical functional connectivity (network-based statistic); changes in effective connectivity among identified network nodes (spectral dynamic causal modeling with parametric empirical Bayes); changes in global and nodal topological properties of whole-brain functional networks (clustering coefficient, shortest path length, nodal degree, nodal efficiency; Schaefer-400 atlas); and associations between brain network changes and changes in obesity-related indicators.