Ultra-processed Food Reducing Intervention and Continuous Glucose Monitoring

The goal of this trial is to investigate whether reduction in ultra-processed food intake through diet counseling and education can improve postprandial glucose levels and glycemic variability among Korean healthy adults aged 20-30 years. The main questions it aims to answer are: * Does the reduction in ultra-processed food intake lower postprandial glucose levels and glycemic variability in healthy adults without a history of diabetes? * Does the reduced intake in different ultra-processed food subgroups and items differentially influence postprandial glucose and glycemic variability? * Does other dietary and lifestyle factors (physical activity, sleep, smoking) alter the association between ultra-processed food intake reduction and glycemic variability? Participants will: * Undergo the 10-day pre-intervention monitoring period, during which each participant will wear a continuous glucose monitoring (CGM) device and concurrently report their daily dietary intakes (all food and beverage consumptions) and other lifestyle behaviors (sleep, smoking, physical activity) * After the 10-day pre-intervention monitoring period, participants will be randomized to either intervention or control group * Intervention group: Participants will visit the research site to receive dietitian-led nutrition education and personalized diet counseling targeting reduction of ultra-processed food intake, as well as improving diet quality. Personalized diet counseling will be provided by study dietitian based on participant\'s records of dietary intakes during the 10-day pre-intervention monitoring period. * Control group: Participants will receive dietitian-led nutrition education and personalized diet counseling targeting general improvement in nutrient intake (based on the national dietary guidelines). * After the intervention, participants will undergo the 10-day post-intervention monitoring period, during which participants will wear a new CGM device for an additional 10 days and continue daily reporting of dietary intakes (all food and beverage consumptions) and lifestyle behaviors (sleep, smoking, physical activity).