Maternal over-nutrition during pregnancy is a risk factor for pregnancy complications and is increasingly associated with adverse childhood outcomes such as increased propensity for obesity and metabolic disease. However, there is emerging evidence that parental lifestyle factors prior to and at conception have a powerful impact on the health of the offspring for more than one generation. Maternal and paternal obesity prior to conception alters the molecular composition of both oocytes and sperm, which can partly escape epigenetic reprogramming at fertilization, altering the developmental trajectory of the resultant embryo, ultimately increasing the incidence of obesity and metabolic disorders in offspring. Understanding the molecular underpinning of these changes may help create interventions to reduce the risk of disease in future generations.