Age-Stratified Trends in Nutrition and Lifestyle Transitions in Korea: Findings from KNHANES 2013–2022

<b>Background:</b> Rapid aging and dietary Westernization in Korea have raised concerns about shifting nutrition and lifestyle patterns. <b>Objectives:</b> This study examined 10-year trends in nutrient intake, biochemical indicators, meal-related behaviors, and sedentary time among Korean adults, stratified by age group. <b>Methods</b>: Data were drawn from the 6th-9th waves (2013-2022) of the Korea National Health and Nutrition Examination Survey (KNHANES) for a cross-sectional analysis, including 61,688 participants (18-39 years: 17,225; 40-64 years: 28,045; ≥65 years: 16,218). Survey-weighted linear and logistic regression analyses were used to test linear trends and between-period contrasts (2013-2015 vs. 2020-2022). <b>Results</b>: Total energy intake declined significantly from 2087 kcal in 2013-2015 to 1823 kcal in 2022 (<i>p</i> for trend < 0.001), accompanied by a decrease in carbohydrate share (62.8% to 58.3%, <i>p</i> < 0.001) and increases in protein (13.8% to 15.4%, <i>p</i> < 0.001) and fat (19.0% to 23.4%, <i>p</i> < 0.001). Saturated fat and cholesterol intake increased significantly, particularly among older adults (+50.9% and +46.4%, respectively; both <i>p</i> < 0.001). The proportion of breakfast skippers increased significantly, more than 35% in 2022 (<i>p</i> < 0.001). Conversely, the frequency of eating out decreased (<i>p</i> < 0.001), with a particularly pronounced decline during the COVID-19 period. Sedentary time steadily and significantly increased over the decade (<i>p</i> < 0.001). <b>Conclusions</b>: Over the past decade, Korean adults have shifted toward lower energy and carbohydrate intake, higher protein and fat consumption, and more sedentary lifestyles. Differences in vulnerability by age emphasize the need for personalized public health strategies: promoting protein intake and reducing sedentary time for older adults, while improving dietary patterns and managing weight for younger generations.