Aim: This study was designed to understand the changes in dietary and lifestyle behaviours that are major determinants of health during the COVID-19 outbreak. Methods: A cross-sectional study was conducted through an online questionnaire using a convenience sample of 415 adults living in Kuwait (age range 18-73 years). Results: The overall prevalence of being overweight and obesity among participants was 37.2% and 33.1% respectively. The study identified significant changes in the dietary habits and lifestyle behaviours of participants during COVID-19. In general, there was an increase in the percentage of participants that consumed four or more meals a day, skipped breakfast, and engaged in frequent late night snacking. Moreover, there was a drastic decrease in the frequency of fast food consumption and an increase in the percentage of participants who had their main meal freshly made. Furthermore, there was a great reduction in physical activity and an increase in the amount of screen time and sedentary behaviours. A notable increase was detected in day-time sleep and a decrease in night-time sleep among participants. Conclusion: This study indicates that due to the increased prevalence of habits conducive to increased rates of being overweight and obesity during the COVID-19 outbreak, there is a high likelihood that the pandemic will further exacerbate the already widespread problem of obesity and being overweight in Kuwait.