Type 2 diabetes mellitus is one of the most important public health problems in the world. Its increasing prevalence in several countries and the difficult metabolic control of individuals with the disease justify studying strategies for primary prevention. Recent randomized clinical trials suggest that nutritional intervention may have an important impact on risk reduction for type 2 diabetes mellitus among individuals at high risk. The present systematic review describes the effect of lifestyle intervention trials on primary prevention of type 2 diabetes mellitus.