Effects of ultra-processed food reduction intervention on postprandial glucose and glycaemic variability in Korean young adults: study protocol for the ULTRA-CGM randomised controlled trial.

introductionHigh intake of ultra-processed foods (UPFs) is associated with an increased risk of type 2 diabetes. However, evidence from randomised controlled trials evaluating the effect of UPF reduction on postprandial glucose responses and glycaemic variability in young adults is limited. The Ultra-Processed Food Reduction Intervention and Continuous Glucose Monitoring (ULTRA-CGM) trial aims to evaluate the effects of a UPF-reducing dietary intervention on postprandial glucose responses and glycaemic variability in healthy Korean young adults. METHODS AND ANALYSIS: This is a parallel, two-arm randomised controlled trial enrolling 50 participants (aged 20-39 years) with UPF intake ≥25% of daily energy. Following a 10-day baseline monitoring period using CGM and lifestyle diaries, participants are randomised 1:1 to a 40-minute one-on-one UPF-reducing dietary intervention or a 40-minute one-on-one standard dietary counselling based on national dietary guidelines (control). The intervention focuses on reducing UPF consumption, with participants counselled to maintain their usual total energy intake and lifestyle behaviours. After the intervention, participants undergo a 10-day CGM monitoring period and lifestyle diaries. The primary outcome is the change in postprandial glucose responses, quantified as 2-hour incremental area under the curve following meals, from baseline to postintervention. Secondary outcomes include changes in glycaemic variability metrics (coefficient of variation, SD, mean amplitude of glycaemic excursions, glucose spike frequency), time-in-range metrics, body weight, waist circumference, body composition, blood pressure and handgrip strength. For the analyses, between-group differences will be evaluated using analysis of covariance adjusting for baseline values, with daily CGM data analysed using linear mixed-effects models. This trial will provide evidence on whether targeted reduction of UPFs improves postprandial glucose control and glycaemic variability in healthy young adults. ETHICS AND DISSEMINATION: This study is approved by the Korea University Institutional Review Board (KUIRB-2025-0600-05). It will be conducted in accordance with the principles of the Declaration of Helsinki and the principles of the International Conference on Harmonisation Good Clinical Practice guidelines. Results will be disseminated through publications, academic conferences, PhD dissertation and social and lay media. TRIAL REGISTRATION NUMBER: NCT07175701.