BackgroundA poor diet contributes substantially to the development of noncommunicable diseases. In Singapore, it is recommended to consume at least 2 servings of fruits and vegetables daily to reduce the risk of developing noncommunicable diseases. However, the adherence rate among young adults is low. The COVID-19 pandemic has led to frequent users of mobile food delivery apps (MFDAs) adopting unhealthy eating habits, including high consumption of sugar-sweetened beverages, making it crucial to gain a deeper understanding of the underlying factors driving their use patterns.ObjectiveWe aimed to examine the use patterns of MFDAs among young adults during the COVID-19 pandemic; investigate the association between MFDA use and sociodemographic factors, dietary factors, and BMI; identify the underlying reasons for the observed use patterns of MFDAs among users; and compare the influences of MFDA use between frequent and infrequent users.MethodsA sequential mixed methods design was used involving a web-based survey and in-depth interviews with a subset of respondents. Poisson regression and thematic analysis were used to analyze the quantitative and qualitative data, respectively.ResultsThe quantitative results revealed that 41.7% (150/360) of participants reported using MFDAs frequently, defined as at least once a week. Although not substantial, the study found that frequent users were less likely to consume 2 servings of vegetables per day and more likely to drink sugar-sweetened beverages. Nineteen individuals who had participated in the quantitative component were selected for and completed the interviews. Qualitative analysis identified 4 primary themes: deliberations about other sources of meals versus meals purchased via MFDAs, convenience is vital, preference for unhealthy meals ordered from MFDAs most of the time, and cost is king. Before making any purchase, MFDA users consider all these themes at the same time, with cost being the most important influential factor. A conceptual framework based on these themes was presented. Lack of culinary skills and COVID-19 restrictions were also found to influence frequent use.ConclusionsThis study suggests that interventions should focus on promoting healthy dietary patterns in young adults who frequently use MFDAs. Teaching cooking skills, especially among young male individuals, and time management skills could be useful to reduce reliance on MFDAs. This study highlights the need for public health policies that make healthy food options more affordable and accessible. Given the unintended changes in behavior during the pandemic, such as reduced physical activity, sedentary behavior, and altered eating patterns, it is essential to consider behavior change in interventions aimed at promoting healthy lifestyles among young adults who frequently use MFDAs. Further research is needed to evaluate the effectiveness of interventions during COVID-19 restrictions and assess the impact of the post–COVID-19new normalon dietary patterns and physical activity levels.