Background: During the Covid-19 pandemic the Dutch government implemented its so-called 'intelligent lockdown' in which people were urged to leave their homes as little as possible and work from home. This life changing event may have caused changes in lifestyle behaviour, an important factor in the onset and course of diseases. The overarching aim of this study is to determine life-style related changes during the first wave of the COVID-19 pandemic among a representative sample of the adult population in the Netherlands. Methods: Life-style related changes were studied among a random representative sample of the adult population in the Netherlands using an online survey conducted from 22 to 27 May 2020. Differences in COVID-19-related lifestyle changes between Complementary and Alternative Medicine (CAM) users and non-CAM users were determined. The survey included a modified version of the I-CAM-Q and 26 questions on lifestyle related measures, anxiety, and need for support to maintain lifestyle changes. Results: 1004 respondents were included in the study, aged between 18 and 88 years (50.7% females). Changes to a healthier lifestyle were observed in 19.3% of the population, mainly due to a change in diet habits, physical activity and relaxation, of whom 56.2% reported to be motivated to maintain this behaviour change in a post-COVID-19 era. Fewer respondents (12.3%) changed into an unhealthier lifestyle. Multivariable logistic regression analyses revealed that changing into a healthier lifestyle was positively associated with the variables 'Worried/ Anxious getting COVID-19' (OR: 1.56, 95% C.I. 1.26-1.93), 'CAM use' (OR: 2.04, 95% C.I. 1.38-3.02) and 'stress in relation to financial situation' (OR: 1.89, 95% C.I. 1.30-2.74). 'Age' (OR 18-25: 1.00, OR 25-40: 0.55, 95% C.I. 0.31-0.96, OR 40-55:0.50 95% C.I. 0.28-0.87 OR 55+: 0.1095% C.I. 0.10-0.33), 'stress in relation to health' (OR: 2.52, 95% C.I. 1.64-3.86) and 'stress in relation to the balance work and home' (OR: 1.69, 95% C.I. 1.11-2.57) were found ...