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

Abstract

Background: 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.

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

Design: 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.

Results: 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).

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

Keywords: 24-h dietary recall; Nova classification system; diet quality; diet recall methods; nutrition; ultraprocessed foods.