Potential misclassification of ultra-processed foods across studies and the need for a unified classification system: a scoping review.

The lack of a standardized classification system poses challenges for accurately assessing ultra-processed food (UPF) consumption in Korea. This scoping review compared the UPF consumption levels reported in Korean studies and analyzed the discrepancies to highlight the need for a unified UPF classification system tailored to Korea. Four online databases were searched to identify studies conducted in Korea. From 147 papers, 20 papers that examined UPFs as the main variables were selected and reviewed. Their consumption levels are reported. Ninety percent of the papers were cross-sectional studies, while 10% were prospective cohort studies. Most studies (72%) measured UPF consumption using the 24-h dietary recall (24HR), while 28% used food frequency questionnaires (FFQs). The most popular topic (65%) was the association between UPF consumption and health outcomes, with obesity-related outcomes being examined most frequently. A wide range of UPF consumption was observed: from 4.9% to 32.8% of total energy intake. The estimates from food-based FFQs were the lowest compared to those from the dish-based FFQs or 24HR. Significant variations in UPF consumption levels were observed across dietary assessment methods, researchers, and data sources. This scoping review highlights the need for an objective and standardized UPF classification system, developed through collaboration among researchers, to minimize the potential misclassification issues when estimating UPF consumption or examining its associations with the health outcomes in Korea. Establishing a "UPF Working Group" could serve as an effective starting point for this initiative, and it is expected to attract participation from more researchers interested in UPF studies.