Cities for Better Health Childhood Obesity Prevention Initiative in JAPAN

The primary outcome is the BMI z-score, calculated using the WHO 2007 Growth Reference. This metric standardizes a child's relative weight status by adjusting for both age and sex, enabling comparisons across different age groups and sexes. It represents the number of standard deviations a child's BMI is from the mean BMI of a healthy reference population. The BMI z-score allows for monitoring obesity-related changes over time and assessing the intervention's effectiveness in preventing excessive weight gain. The use of this z-score ensures consistency with international standards, facilitating global comparison of childhood obesity trends. The analysis will focus on changes in BMI z-score from baseline to 1-year and 2-year follow-ups.

HRQoL will be assessed using the KIDSCREEN-10 index, a validated, self-reported measure capturing children's subjective well-being across physical, emotional, social, and school functioning. This 11-item scale uses a 5-point Likert response for each item, which is then converted into a standardized T-score, further transformed to a 0-100 scale. On this scale, higher scores indicate better perceived quality of life. Changes in KIDSCREEN-10 scores will be tracked from baseline through 1-year and 2-year follow-ups to evaluate the intervention's impact on children's overall well-being.

Physical activity will be assessed using self-reported daily minutes of moderate-to-vigorous physical activity (MVPA) and sedentary screen time. Participants will report time spent in activities such as sports, cycling, or active play, as well as screen-based sedentary behaviors. Data will be collected at baseline, 1-year, and 2-year follow-ups to evaluate the intervention's impact on physical activity patterns and sustained behavioral changes. Interpretation will be guided by international guidelines on daily activity targets.

Dietary outcomes will be assessed using the adapted Diet Quality Questionnaire (DQQ). This questionnaire evaluates children's usual intake of key food groups and dietary patterns. Participants or guardians will report the frequency of consuming various categories, including fruits, vegetables, whole grains, protein sources, dairy products, snacks, and sugary drinks. The DQQ aligns with global dietary guidelines and calculates scores reflecting dietary diversity and balance. Data will be collected at baseline, 1-year, and 2-year follow-ups to assess changes in dietary habits and the intervention's effects on promoting healthier eating patterns.