Elucidating the optimal macronutrient composition for dietary management of gestational diabetes mellitus has enormous potential to improve perinatal outcomes. Diet therapy may result in significant cost savings if effective in deterring the need for expensive medical management within this growing population. In only 6 randomized controlled trials in 250 women, data suggest that a diet higher in complex carbohydrate and fiber, low in simple sugar, and lower in saturated fat may be effective in blunting postprandial hyperglycemia, preventing worsened insulin resistance and excess fetal growth. The use of diet in gestational diabetes mellitus remains an area in grave need for high-quality randomized controlled trials.