The goals of medical nutrition therapy for gestational diabetes mellitus (GDM) are to meet the maternal and fetal nutritional needs, as well as to achieve and maintain optimal glycemic control. Nutrition requirements during pregnancy are similar for women with and without GDM. The American Diabetes Association and the American College of Obstetrics and Gynecology recommend nutrition therapy for GDM that emphasizes food choices to promote appropriate weight gain and normoglycemia without ketonuria, and moderate energy restriction for obese women. Current controversies in GDM nutrition therapy involve manipulation of dietary composition (amounts and types of carbohydrates and fats), gestational weight gain, and energy and carbohydrate restriction. Randomized controlled trials are needed to determine which dietary compositions and patterns promote normoglycemia as well as optimal maternal and infant outcomes. Until better evidence is available, nutrition therapy will remain a cornerstone of GDM management with potential benefits that cannot be fully realized in clinical practice.