Validity of the PortionSize App for Assessing Children's Dietary Intake: Results From a Pilot Study Conducted in Controlled and Free‐Living Settings

BACKGROUND: PortionSize is a mobile app that allows users to assess dietary intake and provide feedback in real-time. OBJECTIVE: To assess the validity of the PortionSize app for estimating children's dietary intake when assessed by the children themselves (phase 1) and relative agreement of the app when assessed by their parents (phase 2). METHODS: This pilot study recruited 31 child/parent dyads. Each dyad was trained on the PortionSize app to assess dietary intake. In phase 1, children (7-12 years) assessed dietary intake in a controlled setting, and their assessments were compared with weighed meals. In phase 2, parents assessed their child's dietary intake in a free-living setting, and the criterion measure was the digital photography of foods (DPF) method. RESULTS: Children's energy intake assessments using PortionSize were equivalent to weighed meals (p < 0.05, effect size: 0.22), while energy intake estimates by parents using PortionSize were not equivalent to the DPF method (p > 0.05, effect size: 0.26). The mean percent error between the measurements was 9.1% in phase 1 and 16.5% in phase 2. CONCLUSIONS: The findings suggest PortionSize may be accurate in controlled settings when used by children. In a free-living setting when used by parents, results indicated PortionSize needs improvements in methods for estimating portion size and food identification. The study findings from phase 2 reflect feasibility and relative agreement rather than validation against true intake. This pilot study focuses on initial validity, relative agreement, and user satisfaction, indicating potential for future clinical and community-based pediatric dietary and weight management applications. TRIAL REGISTRATION: NCT05587816 (https://clinicaltrials.gov/study/NCT05587816?term=PortionSize%20app&rank=1).