Reliability and validity of assigning ultraprocessed food categories to 24-h dietary recall data

The Nova classification system categorizes foods into 4 processing levels, including ultraprocessed foods (UPFs). Consumption of UPFs is extensive in the United States, and high UPF consumption is associated with chronic disease risk. A reliable and valid method to Nova-categorize foods would advance understanding of UPF consumption and its relationship to health outcomes.

Test the reliability and validity of training coders and assigning Nova categories to individual foods collected via 24-h dietary recalls.

A secondary analysis of 24-h dietary recalls from 610 children who participated in a randomized controlled trial and were 3-5 y old at baseline was conducted. The Nutrition Data System for Research (NDSR) software was used to collect 2-3 dietary recalls at baseline and yearly for 3 y. Trained and certified coder pairs independently categorized foods into one of 4 Nova categories (minimally processed, processed culinary ingredients, processed, and ultraprocessed). Interrater reliability was assessed by percent concordance between coder pairs and by Cohen's κ coefficient. Construct validity was evaluated by comparing the average daily macronutrient content of foods between Nova categories.

In 5546 valid recall days, 3099 unique foods were categorized: minimally processed (18%), processed culinary ingredients (0.4%), processed (15%), and ultraprocessed (67%). Coder concordance = 88.3%, and κ coefficient = 0.75. Descriptive comparisons of macronutrient content across 66,531 diet recall food entries were consistent with expectations. On average, UPFs were 62% (SD 19) of daily calories, and a disproportionally high percentage of daily added sugar (94%; SD 16) and low percentage of daily protein (47%; SD 24). Minimally processed foods were 30% (SD 17) of daily calories, and a disproportionally low percentage of daily added sugar (1%; SD 8) and high percentage of daily protein (43%; SD 24).

This method of Nova classifying NDSR-based 24-h dietary recalls was reliable and valid for identifying individual intake of processed foods, including UPFs.