The study examines the impact of the COVID-19 lockdown on dietary habits and consumer behaviors in Poland. A cross-sectional online survey of 1097 adult Poles was conducted during the nationwide quarantine. The results show that over 43% and nearly 52% of respondents reported eating and snacking more, respectively, with these tendencies being more frequent among overweight and obese individuals. Almost 30% experienced weight gain, and over 18% experienced weight loss. Overweight, obese, and older subjects (aged 36–45 and >45) were more likely to gain weight, while underweight individuals tended to lose weight further. Increased BMI was associated with less frequent consumption of vegetables, fruits, and legumes, and higher adherence to meat, dairy, and fast-foods. Alcohol consumption increased in 14.6% of respondents, with a higher tendency among alcohol addicts. Over 45% of smokers reported increased smoking frequency during the quarantine. The study highlights the need for organized nutritional support during future epidemic-related quarantines, particularly for vulnerable groups such as overweight and obese individuals.The study examines the impact of the COVID-19 lockdown on dietary habits and consumer behaviors in Poland. A cross-sectional online survey of 1097 adult Poles was conducted during the nationwide quarantine. The results show that over 43% and nearly 52% of respondents reported eating and snacking more, respectively, with these tendencies being more frequent among overweight and obese individuals. Almost 30% experienced weight gain, and over 18% experienced weight loss. Overweight, obese, and older subjects (aged 36–45 and >45) were more likely to gain weight, while underweight individuals tended to lose weight further. Increased BMI was associated with less frequent consumption of vegetables, fruits, and legumes, and higher adherence to meat, dairy, and fast-foods. Alcohol consumption increased in 14.6% of respondents, with a higher tendency among alcohol addicts. Over 45% of smokers reported increased smoking frequency during the quarantine. The study highlights the need for organized nutritional support during future epidemic-related quarantines, particularly for vulnerable groups such as overweight and obese individuals.