To estimate food intake, the nutrient content of food must be known or inferred by matching it to a nutrient database. This study evaluated how different procedures for matching foods to the Food and Nutrient Database for Dietary Studies (FNDDS) affect food intake estimates. Adult participants estimated a meal with the PortionSize app, which contains a subset of FNDDS codes (PortionSize FNDDS). Meals were covertly weighed (weigh back), and intake was estimated by referencing the FNDDS dataset. Combination foods were evaluated by 1) a composite generated by summing the nutrient values (from FNDDS) from single food items and 2) using the single composite food code from FNDDS. Raters analyzed food images from the PortionSize app to estimate intake with the digital photography of foods (DPF) method. Raters estimated intake from: 1) PortionSize FNDDS and 2) full FNDDS. Using PortionSize's FNDDS database, participants' energy intake estimates were equivalent to rater estimated energy intake. Raters estimated almost identical energy intake when they used PortionSize vs. full FNDDS. Using the full FNDDS, the DPF's energy estimates were similar to weigh back. Estimation of energy intake with a single FNDDS code was not equivalent to estimations from summing the nutrient values for combination foods.
Keywords: Energy intake estimation; PortionSize; dietary assessment; digital photography of foods; food composition; food selection; mHealth; nutrients.