Healthy diet and supplement use may prove as sustainable strategies to lower COVID-19 infection. Our study investigated the dietary changes before and during lockdown and observed dietary supplements (DS) use among residents in Saudi Arabia. This cross-sectional study collected data via an online electronic survey questionnaire among males (N = 921) and females (N = 1044) residing in Saudi Arabia, 15 years of age and above. There was a significant decrease in the prevalence of males (before vs. during lockdown) having improved changes in dietary habit (68.6% vs. 65.8%; p = 0.004), which was similar in female participants (69 vs. 73.4% vs. 69%; p < 0.001). The frequency of multivitamin users among COVID-19 participants was significantly lower than non-users (44.4 vs. 55.6; p < 0.003). Male respondents within 26-35 years of age were more likely to use multivitamin supplements than females (30.1 vs. 22.6%; p < 0.05) of same age group. Predictors for DS use were increased age group, income, education level and COVID-19 status. In conclusion, an increase in unhealthy diet behavior was observed among Saudi males and females during the pandemic lockdown and the predictors of DS use included increased age, income, education level and COVID-19 status.