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 dietary counseling and education can improve postprandial glucose responses and glycemic variability compared with a usual diet in young, healthy Korean adults aged 20-30 years. The main questions it aims to answer are: \- Does reducing ultra-processed food intake, while maintaining total energy intake and usual lifestyle behaviors, improve postprandial glucose and lower glycemic variability in healthy adults without diabetes? 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 consumption) 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 one-on-one nutrition education and personalized dietary counseling targeting reduction of ultra-processed food intake. 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 dietary counseling 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).

The Ultra-Processed Food Reduction Intervention and Continuous Glucose Monitoring (ULTRA-CGM) trial is a parallel, two-arm randomized controlled trial designed to evaluate the effects of a ultra-processed food (UPF)-reducing dietary intervention on postprandial glucose responses and glycemic variability in young Korean adults (aged 20-39 years) using CGM devices. Participants will be randomly assigned to either a UPF-reducing intervention group or a control group maintaining their usual diet. We hypothesize that receiving the UPF-reducing dietary intervention will improve postprandial glucose responses and reduce glycemic variability compared with participants receiving standard dietary counseling based on national guidelines. The findings from this trial may provide experimental evidence on the metabolic effects of reducing UPF consumption and inform dietary strategies for diabetes prevention among younger adults.

Inclusion Criteria: 1. Korean adults aged 20-39 years 2. Not currently pregnant 3. No personal history of diabetes or other glucose-related conditions 4. Consume ≥25% of daily energy intake from UPFs, as assessed by an online, self-administered semi-quantitative screening food frequency questionnaire (FFQ) 5. No restriction on wearing a CGM device 6. No increased risk of bleeding 7. No prior adverse reaction to CGM devices 8. Willingness to participate in follow-up assessments Exclusion Criteria: 1. Unable to maintain continuous follow-up during the study period (e.g., due to special plans such as traveling) 2. Planning to follow a special or restrictive diet (e.g., for weight loss) during the study period