Supplying adequate human nutrition within ecosystem carrying capacities is a key element in the global environmental sustainability challenge. Life cycle assessment (LCA) has been used effectively to evaluate the environmental impacts of food production value chains and to identify opportunities for targeted improvement strategies. Dietary choices and resulting consumption patterns are the drivers of production, however, and a consumption-oriented life cycle perspective is useful in understanding the environmental implications of diet choices. This review identifies 32 studies that use an LCA framework to evaluate the environmental impact of diets or meals. It highlights the state of the art, emerging methodological trends and current challenges and limitations to such diet-level LCA studies. A wide range of bases for analysis and comparison (i.e., functional units) have been employed in LCAs of foods and diet; we conceptually map appropriate functional unit choices to research aims and scope and argue for a need to move in the direction of a more sophisticated and comprehensive nutritional basis in order to link nutritional health and environmental objectives. Nutritional quality indices are reviewed as potential approaches, but refinement through ongoing collaborative research between environmental and nutritional sciences is necessary. Additional research needs include development of regionally specific life cycle inventory databases for food and agriculture and expansion of the scope of assessments beyond the current focus on greenhouse gas emissions.