This research investigated the prevalence and incidence of COVID-19 infection among Seventh-day Adventist Christians in the UK compared to non-Adventists and assessed the pandemic's impact on their health and dietary intake. Seventh-day Adventists and non-Adventists in the UK completed an online survey, including a Food Frequency Questionnaire, a 24-h dietary recall, and health and lifestyle questions. Participants were followed for 2 years to determine COVID-19 incidence rates. The baseline survey was completed by 170 people, 86 of whom were Adventists. The follow-up at 2 years showed a significantly lower self-reported COVID-19 incidence among Adventists (OR 0.45, 95% CI 0.2, 1.0, p = 0.05). The incidence rate among Adventists was 65.48 per 1000 person-years versus 121.79 per 1000 person-years among non-Adventists. Adventists were less likely to experience long COVID (OR 0.30, 95% CI 0.12, 0.78, p = 0.01). Despite being older, Adventists had a significantly lower COVID-19 incidence rate. The Adventist lifestyle, including healthy eating habits, fasting, a plant-based diet, and abstaining from alcohol and coffee, was prevalent in this sample. More research is needed to explore the association between the Adventist lifestyle and infectious disease.