Food has the power to heal. Our bodies transform and are transformed by the elements in food, and the adage that we are what we eat is true. The twentieth century nutrition science focused on decoding the processes and building blocks of this transformation—proteins, fats, carbohydrates, vitamins, and minerals. Twenty-first-century nutrition science is aimed at better understanding the increasingly appreciated bioactive substances within the food matrix that help regulate this transformation—fibers, phytonutrients, bioactive fats, and ferments. Our microbiome and the mitochondria play a key function in orchestrating the role of bioactives in health and are inspiring next-generation nutritional approaches for addressing over- and undernutrition.