Dietary changes that occur in response to economic development are collectively known as the nutrition transition. More specifically, diets built around staple cereals and tubers give way to diets with more animal products and more added sugars and fats. Although the proportion of dietary protein stays constant, plant proteins are replaced by animal proteins but in ways that are dependent on regional cultural, religious, and ethical concerns. The protein transition, viewed here as a subset of the broader nutrition transition, illustrates how dietary patterns in low- and middle-income countries are shaped by societal as well as by economic forces. The complexity of food decisions justifies the need to integrate nutrition with the social sciences in the study of evolving food systems.