The environmental and nutritional attributes of different food types can vary greatly. Consequently, diets composed of different sets of food types, will differ in their environmental footprints, and in their nutritional quality; so affecting human health. When such differences are multiplied by many millions of people, the overall effect is considerable. Human diets are, therefore, an important point of interconnection in food systems via which change is driven – for better or worse – by shifts how people consume. At least in theory, diets might provide a means by which to achieve both health and environmental goals simultaneously. But the reality is not so simple. Understanding these complexities, helps provide a window on both the opportunities and difficulties of taking a food systems approach, and on the important role that diets play.

A central topic of most debates on sustainable food systems is the complex role of livestock, meat and dairy. This is due to their connection to many issues of moral and practical concern related to food systems; affecting both humans and the environment, and animal's own interests. The picture is complex. And because different stakeholders bring different worldviews and perspectives, people often disagree about the appropriate role of livestock, meat, and dairy, in sustainable food systems. Yet demand for meat and dairy consumption is expected to grow considerably, and as a result, debates around livestock-related issues are becoming increasingly prominent. Understanding these helps to provide a broader understanding of food systems more generally.