Project Summary/Abstract Dental caries is one of the most significant public health challenges in Alaska Native communities. Added sugars from fruit drinks, especially Kool-Aid, are the main behavioral risk factor for caries. Our team developed and implemented a community-based intervention targeting sugared fruit drinks in Alaska Native children (NIDCR Grant No. U01DE027629). The six-month intervention consisted of health education delivered by a trained indigenous Community Health Worker, who taught families about the harms caused by sugared fruit drinks, introduced sugar-free alternatives, and provided parents with self-efficacy training to facilitate the switch. Local stores were recruited to sell sugar- free Kool-Aid. We enrolled 201 Alaska Native children ages 1 to 10 years; 143 children in two communities received the intervention and 58 children a third community were in the delayed treatment control group. The trial ended in March 2023. Our team is currently evaluating the intervention. The main trial outcome is change in added sugar intake from baseline to 6m, measured using a validated hair biomarker. The trial did not include a disease outcome, but we collected supragingival plaque samples from children throughout the trial (baseline, 1m, 3m, 6m) and archived them for future study. We now have tribal permissions to analyze the plaque. The goal of this 2-year R03 is to process and analyze the 594 banked plaque samples. The Aims are to: (1) Assess the relationship between added sugar intake and the oral microbiome in Alaska Native children; and (2) Conduct mediator analyses to examine the effects of the intervention on the microbiome with added sugar as the mediator. We will test the primary hypothesis that lower added sugar intake is associated with increased alpha diversity, which is a signature of a healthy microbiome. The proposed work will be the first known study to evaluate how added sugar impacts the microbiome in Alaska Native children and is expected to provide insight on mechanisms of the original behavioral trial. The knowledge gained will be critical in refining future interventions aimed at reducing added sugar intake, preventing caries, and addressing oral health inequities that disproportionately affect Indigenous communities.