Introduction and objective:
The COVID-19 pandemic has been associated with changes in health-related behaviours, including dietary patterns. The aim of this study was to compare dietary habits, nutritional intake, and selected health parameters in adult populations assessed before and during the COVID-19 pandemic.

Material and methods:
The analysis was based on two groups from the population-based Białystok PLUS cohort: pre-pandemic (n=565) and during-pandemic (n=637). Dietary intake, lifestyle factors, and clinical measurements were compared. Statistical analyses were adjusted for seasonality using IBM SPSS Statistics 27.0.

Results:
Participants assessed during the pandemic reported higher consumption of vegetables, particularly root and cruciferous types, legumes, and water, and demonstrated greater adherence to Mediterranean and Nordic dietary patterns. At the same time, higher levels of sedentary behaviour and screen exposure were observed. Clinically, the pandemic-period group presented lower waist-to-hip ratio, blood pressure, LDL and HDL cholesterol, and interleukin-6 levels. Despite these objectively more favourable dietary patterns, self-rated diet quality was lower.

Conclusions:
Significant differences in dietary behaviours, lifestyle factors, and selected health parameters were observed between adult populations assessed before and during the COVID-19 pandemic. The findings indicate the coexistence of both beneficial and adverse behavioural patterns, underscoring the importance of integrated public health strategies addressing diet quality, physical activity, and health awareness.