Impact of eating window and diet composition on obesity: a comparative study of adults in the USA and South Korea

Abstract Background Dietary habits influence weight management and metabolic health. This study examined trends in eating window and diet composition, and their correlation with obesity among adults. Methods Data from the U.S. National Health and Nutrition Examination Surveys (NHANES) and South Korea’s Korean National Health and Nutrition Examination Survey (KNHANES) (2007–2020) were analyzed. The study assessed eating window, diet composition, and obesity. The eating window was defined from the first energy intake after waking up to the last before bed. Diet composition was linked to respective national food databases. Results Both countries saw increased snack consumption and body mass index (BMI) over 14 years. Korean adults showed the lowest obesity rates with an 8–9 hour eating window, while U.S. adults had the lowest rates with an 8–11 hour window. Macronutrient analysis revealed Korean breakfasts were carbohydrate-rich, while dinners included higher protein and alcohol intake. Conclusions Koreans have shorter eating windows and lower BMI than U.S. adults. This suggests the potential benefits of time-restricted eating but highlights the need for personalized interventions and further research on individual, cultural, and environmental factors.