Effect of a multilevel blended intervention based on social cognitive theory on fruit and vegetable consumption in students

Inadequate fruit and vegetable (F&V) consumption among adolescents remains a critical global public health challenge. This cluster-randomized controlled trial evaluated the effectiveness of a SCT-based multilevel blended intervention in increasing F&V consumption-frequency scores among female students in grades 7–9 in Seydun, Iran, during 2023–2024. Four public schools were randomized to the intervention (n = 104) or comparison group (n = 101).

The intervention comprised eight weekly 60-minute sessions delivered through a combination of face-to-face and WhatsApp-based activities, with complementary components involving parents and school staff. Outcomes were assessed at baseline and two months after the intervention using a researcher-developed questionnaire with reported evidence of face validity, content validity, internal consistency, and test–retest reliability. Analysis of covariance (ANCOVA) models compared post-intervention scores between groups while adjusting for baseline scores.

The intervention group showed significantly greater improvements in fruit (1.84 to 3.00, p