The lockdown restrictions imposed globally to curb the COVID-19 pandemic have altered many aspects of daily life, including diet and physical activity. The aim of this systematic review was to evaluate evidence for changes in the diet and physical activity habits of older adults due to COVID-19-related lockdowns. We included analytic observational studies that reported on changes in diet, physical activity, or both, among older individuals (≥50 years old). We searched PubMed and EBSCO LISTA to identify original research articles published between 01/2020-03/2021. We identified 27 studies, 5 of which reported on changes in diet, 17 on changes in physical activity, and 5 on changes in both. The sample sizes ranged from 17 to 3110 subjects. Six of 10 papers on diet reported no significant changes in quantity or quality of food consumption; of those who did find changes in diet, these were generally unfavorable. Thirteen of 22 studies on physical activity reported a decrease in physical activity or an increase in sedentary time; the rest reported no major changes. Pre-lockdown habits were a predictor of change in some studies. The safer-at-home measures have not greatly impacted the diet of older adults but have led to a significant decrease in their physical activity, putting them at higher risk for non-communicable diseases, which may further increase their susceptibility to COVID-19. Ultimately, these findings may help guide clinical practice, by promoting additional health screenings by general practitioners for the elderly and by emphasizing the need for lifestyle interventions like at-home exercise initiatives, to help mitigate the negative impact of the pandemic on this especially vulnerable age group.