During the COVID-19 lockdown in Poland, a cross-sectional online survey of 1097 adults revealed significant changes in dietary habits and behaviors. Over 43% of participants reported eating more, and nearly 52% reported snacking more frequently, with these trends more common among overweight and obese individuals. Over 30% experienced weight gain, with an average increase of 3.0 kg, while over 18% lost weight, averaging a decrease of 2.9 kg. Obese individuals and those over 45 years old were more likely to gain weight, while underweight individuals tended to lose more weight. Increased consumption of meat, dairy, and fast food was associated with higher BMI, while vegetable and legume consumption decreased. Alcohol consumption increased in 14.6% of participants, with a higher tendency among alcohol addicts. Over 45% of smokers reported increased smoking frequency during the lockdown. The study highlights that lockdowns can affect eating behaviors and dietary habits, emphasizing the need for organized nutritional support, especially for vulnerable groups like overweight and obese individuals. The pandemic also led to increased fears of contracting SARS-CoV-2 during grocery shopping and food contact, with women and those with lower education levels expressing these fears more frequently. The study underscores the importance of addressing these changes to mitigate long-term health impacts, particularly in vulnerable populations. Limitations include the reliance on self-reported data and potential response bias. Overall, the findings suggest that lockdowns can lead to significant dietary modifications, with potential long-term health consequences.During the COVID-19 lockdown in Poland, a cross-sectional online survey of 1097 adults revealed significant changes in dietary habits and behaviors. Over 43% of participants reported eating more, and nearly 52% reported snacking more frequently, with these trends more common among overweight and obese individuals. Over 30% experienced weight gain, with an average increase of 3.0 kg, while over 18% lost weight, averaging a decrease of 2.9 kg. Obese individuals and those over 45 years old were more likely to gain weight, while underweight individuals tended to lose more weight. Increased consumption of meat, dairy, and fast food was associated with higher BMI, while vegetable and legume consumption decreased. Alcohol consumption increased in 14.6% of participants, with a higher tendency among alcohol addicts. Over 45% of smokers reported increased smoking frequency during the lockdown. The study highlights that lockdowns can affect eating behaviors and dietary habits, emphasizing the need for organized nutritional support, especially for vulnerable groups like overweight and obese individuals. The pandemic also led to increased fears of contracting SARS-CoV-2 during grocery shopping and food contact, with women and those with lower education levels expressing these fears more frequently. The study underscores the importance of addressing these changes to mitigate long-term health impacts, particularly in vulnerable populations. Limitations include the reliance on self-reported data and potential response bias. Overall, the findings suggest that lockdowns can lead to significant dietary modifications, with potential long-term health consequences.