**Background:** Adolescence is a critical period for establishing dietary behaviors that persist into adulthood. The COVID-19 pandemic disrupted lifestyles through school closures, social distancing, and economic contraction, raising concerns about worsening dietary habits—particularly among socioeconomically disadvantaged groups. Previous research has established that household income influences food availability, affordability, and consumption patterns, but few studies had examined how the pandemic differentially affected adolescent dietary behaviors by socioeconomic status.
**Methods:** This study used cross-sectional data from the Korea National Health and Nutrition Examination Survey (KNHANES), comparing 2019 (pre-pandemic) and 2020 (during pandemic) data. The sample included 800 adolescents aged 12–18 years (423 boys, 377 girls) after excluding those reporting <500 kcal/day or >5,000 kcal/day. Household income was used as a measure of socioeconomic status (SES), categorized into quartiles (low, medium-low, medium-high, high). Twelve dietary behavior indicators were assessed: family meals, nutrition education/counseling, nutrition label use, adequate fruit/vegetable intake (≥500 g/day), adequate calcium intake, adequate vitamin A intake, breakfast skipping (≥5 days/week), excessive sodium intake (>2,300 mg/day), excessive fat intake (>30% of total energy intake), excessive sugar intake (≥10% of total energy intake), frequent soft drink consumption (≥5 times/week), and frequent eating out (≥once/day). Statistical analyses used weighted estimates accounting for the KNHANES sampling design, with regression analysis to evaluate differences by year and SES level, including interaction effects.
**Key Results:** During the COVID-19 pandemic, average daily vegetable intake decreased from 170.7 g/day to 149.8 g/day (p=0.07). Breakfast skipping prevalence rose from 33.1% to 37.4% (not statistically significant overall). Frequent soft drink consumption increased significantly from 7.6% to 14.8% (p<0.01), driven primarily by boys (9.5 percentage point increase vs. 4.4 percentage points in girls). Frequent eating out decreased from 46.0% to 36.8% (p<0.05). Among girls only, average sugar intake and excessive sodium intake showed decreasing trends (sodium: 12.7 percentage point reduction). Food insecurity (low or medium-low levels) increased compared to pre-pandemic levels.
When analyzed by SES, striking disparities emerged. Breakfast skipping among low-SES adolescents increased dramatically from 22.1% in 2019 to 56.5% in 2020 (34.4 percentage point increase), while high-SES adolescents showed virtually no change (29.6% to 29.9%; 0.3 percentage point increase). This differential change was statistically significant (p<0.05). Soft drink consumption increased in both groups but more dramatically in low-SES adolescents (from 8.4% to 31.3%; 22.9 percentage point increase) compared to high-SES adolescents (4.6 percentage point increase), though the interaction did not reach statistical significance. During COVID-19, low-SES adolescents also showed lower prevalence of family meals (Δ high-low=11.5%), adequate calcium intake (Δ high-low=4.9%), and eating out (Δ high-low=21.1%), though these differences were not statistically significant.
**Clinical Implications:** The COVID-19 pandemic exacerbated socioeconomic disparities in adolescent dietary behaviors, particularly breakfast skipping. Low-SES adolescents experienced a 34-fold greater increase in breakfast skipping compared to high-SES peers. The concurrent rise in food insecurity and soft drink consumption among disadvantaged groups raises concerns about long-term nutritional and metabolic health consequences, including obesity. School closures disrupted government-funded meal support programs for low-income children, likely contributing to these disparities. The authors recommend continued monitoring of dietary patterns as Korea transitions out of social distancing, and emphasize the need for sustained national-level nutritional support for vulnerable adolescents to prevent the entrenchment of unhealthy dietary behaviors established during this critical developmental period.