Background: Obesity is a major public health concern associated with adverse physical and psychological outcomes, including body shame (BS) and reduced self-esteem (SE). Lifestyle interventions incorporating dietary and exercise components, such as time-restricted eating (TRE), mindful eating, and structured physical activity, have shown promise; however, evidence on their combined effects within scalable, web-based formats remains limited. Objective: This study aimed to evaluate the effectiveness of a multi-component, web-based lifestyle intervention integrating TRE, mindful eating, and structured online exercise on body composition and psychological outcomes in young adults. Methods: In this pilot randomized controlled trial, 42 healthy young adults (age: 20.4 ± 1.6 years) were allocated to either an intervention group (n = 28) or a control group (n = 14). The intervention group followed an integrated program combining TRE, mindful eating principles, and guided online exercise sessions, while the control group received standard dietary and physical activity recommendations. Outcomes included body composition, anthropometric measures, BS (Weight- and Body-Related Shame and Guilt Scale), SE (Rosenberg Self-Esteem Scale), and eating behavior (Three-Factor Eating Questionnaire). Results: Significant group × time interactions were observed for body fat percentage (p < 0.001), fat mass (p = 0.001), and body mass (p = 0.025), with the intervention group demonstrating greater reductions compared with controls. BS scores significantly decreased in the intervention group, whereas no significant between-group differences were observed for SE (p > 0.05). Dietary adherence appeared higher than exercise adherence over the intervention period. Conclusions: A multi-component, web-based lifestyle intervention integrating TRE, mindful eating, and structured exercise may improve body composition and reduce BS in young adults. However, changes in SE were not observed over the short term. These findings support the feasibility of scalable digital lifestyle interventions, while highlighting the need for longer-term studies to clarify psychological outcomes.