Background: University students experience substantial psychological well-being and body-image concerns, while scalable, personalized digital support remains underexamined in Malaysia. Artificial intelligence chatbots may deliver repeated lifestyle guidance, but the incremental value of personalization over structured chatbot support is uncertain. Objectives: This study evaluated changes in psychological well-being and body appreciation following a 12 week personalized AI-powered lifestyle intervention, NExGEN, among Malaysian university students. Methods: A two-arm, controlled, quasi-experimental pre-post study allocated 140 students aged 18 to 35 years by matched blocks to NExGEN (n = 70) or a structured-prompt ChatGPT control (n = 70). NExGEN generated adaptive weekly lifestyle actions from a 47-item onboarding assessment, whereas control participants received standardized weekly prompts covering the same lifestyle domains. Psychological well-being and body appreciation were assessed at baseline and week 12 using the World Health Organization-Five Well-Being Index and Body Appreciation Scale-2. Intention-to-treat linear mixed models estimated adjusted within-group changes and between-group differences in change, with Holm adjustment for the co-primary outcomes. Results: Week-12 assessments were completed by 121 participants (86.43%). In NExGEN, psychological well-being improved by an adjusted 8.68 points (95% CI, 6.22 to 11.14), z = 6.91, p < .001, and body appreciation improved by 0.17 points (95% CI, 0.10 to 0.24), z = 4.82, p < .001. However, between-group differences in change were not statistically significant for psychological well-being (2.87 points; 95% CI, -0.48 to 6.23; z = 1.68; Holm-adjusted p = .093) or body appreciation (0.10 points; 95% CI, 0.00 to 0.19; z = 1.99; Holm-adjusted p = .093). Median platform logins were 68.00 in NExGEN and 58.50 in control; mean acceptability scores were 3.92 and 3.59, respectively. Conclusions: NExGEN participation was associated with significant within-group improvements in psychological well-being and body appreciation, but personalized guidance did not demonstrate superiority over structured chatbot guidance. Because allocation was quasi-experimental, causal attribution remains limited. Randomized component-level trials are needed to determine whether personalization provides incremental benefit.