Expert Authority and Commenter Responses in Weight-Management Communication on Weibo: A Corpus-Assisted Critical Discourse Analysis

Weight management has become an important domain of digital health communication, yet how expert authority is constructed and negotiated in associated comment discourse on Chinese social media remains underexplored. Using Sina Weibo as a case study, this study employed a corpus-assisted critical discourse analysis of 856 expert-mediated weight-management posts and a cleaned analytic corpus of 4265 associated comments. The analysis combined TF–IDF keyword extraction, document-level co-occurrence analysis, topic modelling, automated polarity classification, and qualitative discourse coding to examine how authority was constructed in verified-account health communication and how sampled commenters responded. The findings show that authority was constructed through medicalised explanations, clinical lexicons, biometric parameters, and quantified norms that translated bodily variation into health risks and behavioural targets. Automated classification labelled 91.54% of the cleaned comments as positive, but manual validation of 100 stratified comments identified 31 neutral/mixed cases and substantially weaker performance for negative than for positive comments (macro-F1 = 0.603 on 69 unambiguous positive/negative cases). Model confidence is therefore treated as classification certainty rather than as emotional intensity, and positive labels are not interpreted as compliance or trust. Qualitative analysis assessed compliance, tactical negotiation, embodied resistance, criticism of expert knowledge, and continued biometric self-monitoring. Some commenters challenged particular advice through bodily experience while continuing to use quantified vocabularies of weight, duration, and measurement. We interpret this coexistence as recurring discursive reliance on expert-derived metrics, not as a directly measured psychological effect. The findings show how medicalised and quantified language can structure weight-management communication while remaining open to situated negotiation and embodied counter-evidence.