Introduction: COVID-19 was declared a global pandemic due to the virus’s spread and the danger posed to vulnerable individuals. Scotland introduced lockdown and social isolation measures, reducing time spent outdoors and in public spaces. Increased social isolation has been linked to poorer mental health and well-being, leading to increased alcohol consumption, reduced physical activity (PA) levels, and increased sedentary activities. This study aimed to examine the impact of the lockdown due to the COVID-19 pandemic on physical activity, diet, and hydration in Scottish adults. Methods: A mixed-methods online survey, which utilised both open and closed questions, was used to examine these factors during lockdown from July 2020 to November 2020. Participants were asked about their physical activity, diet, and hydration habits and whether lockdown impacted these. The study was approved by the University of Stirling General University Ethics Panel (GUEP). Results: A total of 297 adults (aged 18-72 y) living in Scotland completed the self-reported questionnaire. The results demonstrated that lockdown measures increased the consumption of healthy and unhealthy food and alcohol. Most participants reported that their PA levels had decreased, with only 22% meeting the guidelines for physical activity when the strength guidelines were included. The participants completed significantly less moderate PA than the guidelines recommend (p<0.001).  Further analyses revealed that were not sufficient levels of strength-based activities completed, and sitting activity increased for nearly all the participants. Conclusions: Hydration habits were not largely impacted during the lockdown; however, alcohol consumption increased amongst the female respondents. The percentage of participants meeting the PA guidelines was significantly low when accounting for strength-based activities. This observation underlines the importance of addressing the impact of social isolation on lifestyle factors such as PA and alcohol intake. The main limitations of this study are the sample size and the utilisation of a self-reported questionnaire; however, the results provide an indicator of the changes in diet, hydration and PA in the Scottish adults during the COVID-19 lockdown, another possible area of future research could include other methods such as the utilisation of accelerometers to quantify the PA of the participants and a 7-days weighed food/fluid diary to estimate the energy, fluids and macronutrients intake.