This study will test whether glucose sensor data can be used to identify the time of day when adults with prediabetes are most likely to have high blood sugar after meals. Participants will first wear a continuous glucose monitor and wrist activity monitor and record meal times for 10 days. These data will be used to classify each participant's personal "glycemic vulnerability window," such as morning, evening, or generally variable patterns.
Participants will then be randomly assigned to either personalized meal timing plus a short walk after their most vulnerable meal, or to an attention-matched control group receiving sleep hygiene and general step-count advice. The main outcome will be the change in post-meal glucose exposure during each participant's vulnerable window after 4 weeks.
Age 30 to 70 years
HbA1c 5.7% to 6.4% within 3 months of screening, or
Fasting plasma glucose 100 to 125 mg/dL on two separate occasions
Body mass index 23 to 40 kg/m²
Current or prior diagnosis of type 1 diabetes or type 2 diabetes
Use of glucose-lowering medication within the past 3 months
Use of systemic corticosteroid medication within the past 3 months
Use of prescription weight-loss medication within the past 3 months
Parallel
Phenotype-Guided Meal Timing and Postprandial Walking
BehavioralParticipants randomized to this arm will receive personalized lifestyle guidance based on their CGM-derived circadian glycemic vulnerability phenotype. During the 10-day run-in period, continuous glucose monitoring, wrist actigraphy, and timestamped meal-photo logs will be used to identify the time window in which each participant has the greatest postprandial glucose exposure. Participants will be advised to shift their highest glycemic-load meal away from their highest-vulnerability window and toward their lowest-vulnerability window where feasible. They will also be instructed to perform a 10-minute brisk walk within 30 minutes after the meal occurring in their highest-vulnerability window on at least 5 days per week. The intervention will be delivered through structured dietitian counseling sessions and brief weekly check-in calls. No calorie restriction, prescribed macronutrient diet, or weight-loss target will be imposed.
Sleep Hygiene and Step-Count Advice
BehavioralParticipants randomized to the active comparator arm will receive standardized sleep hygiene and general physical activity guidance matched for contact time with the intervention arm. Sleep hygiene advice will include maintaining regular sleep and wake times, aiming for adequate sleep duration, and reducing screen exposure before bedtime. Participants will also be advised to increase their average daily step count by approximately 10% above their run-in baseline, with steps distributed freely throughout the day. This arm will not include any advice on meal timing, carbohydrate timing, glycemic vulnerability windows, or postprandial walking. The intervention will be delivered through structured dietitian counseling sessions and brief weekly check-in calls.
Change in Vulnerable-Window Postprandial Glucose Incremental Area Under the Curve
Change from baseline run-in period to week 4 in mean postprandial glucose incremental area under the curve during each participant's pre-specified highest glycemic vulnerability window. Postprandial glucose incremental area under the curve will be calculated from continuous glucose monitoring data over 120 minutes after logged meals using the trapezoidal rule.
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