The objective is to test the accuracy of the PortionSize™ app and the MyFitnessPal© app at measuring energy intake in free-living conditions, tested against the gold-standard, doubly labeled water. Participants will use PortionSize™ and MyFitnessPal apps in separate periods to test the accuracy of the respective apps.

We will recruit adults to use the PortionSize app and the MyFitnessPal free-living conditions. In a within subjects and randomized, counterbalanced design, the accuracy of the PortionSize and MyFitnessPal apps at estimating energy intake in free-living conditions will be tested against the gold-standard, doubly labeled water (DLW), over two non-consecutive four-day periods that should include at least one weekend day and encompass the same days of the week during each period. Participants will be trained in our clinic to use the apps prior to their use in free-living conditions. We will integrate customizable notifications and reminders to remotely prompt participants to record data, resolve data collection problems, etc. These notifications and reminders utilize Ecological Momentary Assessment (EMA) methodology to maximize data collection protocol adherence by reminding participants to capture and send food information at relevant times.

Inclusion Criteria:

• Male or female, age 18-62 years
• Body mass index (BMI) 18.5-50 kg/m2
• Ownership of an iPhone model 9 or later, which the participant is willing to use for the study
• Access to Apple ID, password, and email address and willing to use them during the study
• Willing to use data and any accompanying charges as part of study participation
• Willing to complete all study procedures and adhere to study visit timelines
• Willing to be re-contacted for future research and/or follow-up

Exclusion Criteria:

oHave been 6-month weight unstable (gain/loss >5% last 6 months) and/or active weight loss program

• Any cardiometabolic disorder that significantly affects what or how much people eat
• Active cancer diagnosis or treatment that significantly affects what or how much people eat, excluding some melanomas and other cancers
• PBRC employee, as previous reviewers argued that they are not representative of the community (
• 3rd member of the same household to participate (i.e. the 1st and 2nd members of the household cannot participate simultaneously)
• Women who are currently pregnant or breastfeeding (self-reported)
• Diagnosed with an uncontrolled thyroid disorder (controlled ≥ 3 months of medication)
• Have had or plan to have weight loss surgery (gastric band removal may be allowed at PI discretion)
• Consume >28 alcoholic beverages per week
• Anyone severely immunocompromised
• Serious digestive disorders that significantly affect what or how much people eat Fluid imbalance and/or on diuretic
• Follows a diet mainly consisting of foods that study staff deems unquantifiable for this study (i.e., liquid supplements, gluten-free specialty items) or consumes a high quantity of specialty foods
• Any condition or circumstance that, in the judgement of the PIs, couldimpede study completion

Adults aged 18-62, males and females.