Validity of the PortionSize™ and MyFitnessPal© smartphone apps for estimating dietary intake: A randomized crossover clinical trial.

Background: PortionSize™ is a smartphone app that utilizes augmented reality and portion size templates to facilitate users' food intake estimates. MyFitnessPal© is a commercial app that tracks food intake based on user's portion size estimates. Both apps provide real-time feedback on dietary intake, with PortionSize also providing feedback on intake of MyPlate food groups.

Objective: To test validity of both apps for accurately measuring food intake compared to weighed food.

Methods: In a within-subjects randomized counterbalanced design, we tested validity of both apps for accurately measuring food intake compared to weighed food. In semi-controlled free-living settings, adults received a cooler each day that contained pre-weighed foods and were instructed to consume only food and beverages provided. Participants used PortionSize and MyFitnessPal during 3-day periods separated by ∼1-week with prior training on each app. After study periods, participants completed a User Preference Survey (UPS). Two one-sided t-tests, with ±18% equivalence bounds, were used to test whether energy intake estimated with apps was statistically equivalent to weighed intake.

Results: The analysis sample (n = 44; 1 dropped) consisted of 55% females, with a mean (SD) age of 44 (11) years. PortionSize (P=0.032) and MyFitnessPal (P<0.001) energy intake (kcal) estimates were equivalent to weighed intake (mean percent error 8.0% vs 3.7%; respectively). MyFitnessPal had smaller relative absolute error (P<0.001) for energy intake compared to PortionSize. PortionSize and weighed food group estimations were equivalent for protein intake (P=0.002). Although estimates for vegetables, fruits, and dairy were not equivalent, the magnitude of error was relatively low (<0.5 cup Eq). For the UPS, 82% of participants preferred using MyFitnessPal compared to PortionSize (18%; P<0.001).

Conclusions: In semi-controlled free-living settings, both apps provided equivalent energy intake estimates compared to weighed foods; however, PortionSize showed greater error for energy and lower user preference than MyFitnessPal, highlighting the need for improvements to decrease error and enhance user experience.

Clinical trial registration: NCT05166226, https://clinicaltrials.gov/study/NCT05166226.