Gestational diabetes mellitus (GDM), defined as glucose intolerance with onset or first recognition in pregnancy, is a common pregnancy complication and a growing health concern. GDM has been related to significant short-term and long-term adverse health outcomes for both mothers and offspring. Importantly, this number is increasing with the increasing burden of obesity among women of reproductive age. Collectively, these data highlight the significance of understanding risk factors, in particular modifiable factors, for GDM and of preventing GDM among high-risk populations. Research in the past decade has identified a few diet and lifestyle factors that are associated with GDM risk. This review provides an overview of emerging diet and lifestyle factors that may contribute to the prevention of GDM. It also discusses major methodologic concerns about the available epidemiologic studies of GDM risk factors.