Plant-based foods, including fruit, vegetables, legumes, whole grains, and nuts, are prominent features of healthy dietary patterns. In addition to providing energy and essential micronutrients, plant-based foods contribute thousands of biologically active phytochemicals (plant chemicals that may affect health) to the human diet. While there is ample evidence to support the health benefits of diets rich in fruit, vegetables, legumes, whole grains, and nuts, evidence that these effects are due to specific nutrients or phytochemicals is limited. Although scientists are very interested in the potential for specific phytochemicals to prevent or treat disease, current scientific evidence suggests that plant-based foods are the healthiest phytochemical delivery system.