Background The COVID-19 pandemic upended many aspects of daily life. For some individuals, this was an opportunity to re-evaluate their life and make better choices, while others were overwhelmed with stressors, leading to a deterioration in mental and physical health. Aim The aim of this narrative systematic review is to explore the effects of the COVID-19 pandemic on Mediterranean diet adherence. Methods A systematic literature search was carried out on PubMed, Scopus and Web of Science electronic databases utilising the search terms ‘Mediterranean diet’ AND ‘COVID-19’. This yielded 73 articles that fulfilled the inclusion criteria. Results The data suggests that a substantial proportion of individuals adhered less to the Mediterranean diet during the COVID-19 lockdown period. However, individuals receiving some form of lifestyle intervention had better adherence to the Mediterranean diet than their unassisted counterparts. Conclusion This emphasises the importance of professional support during times of crisis to avoid deterioration of a population's health.