As e-health technology becomes more ubiquitous in our health and health care environments, a flexible, robust understanding of what works and under what circumstances is needed. Traditional meta-analyses tell us how frequently a technology has worked for previous populations, but not why. Realist Reviews can contribute to understanding why interventions work and by extension how results of past studies can be applied to emerging health challenges. The utility of such a method is considered in e-health interventions to address the serious growing challenge of Type 2 diabetes and metabolic syndrome in young people.