A dietitian (or dietician) is an expert in dietetics; that is, human nutrition and the regulation of diet. A dietitian advises people on what to eat in order to lead a healthy lifestyle or achieve a specific health-related goal. Dietitians work in a variety of settings from clinical to community and public policy to media communications. A registered dietitian (RD), or registered dietitian nutritionists (RDN), is a dietitian who meets special academic and professional requirements.