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 to achieve a specific health-related goal.n addition, a large number of registered dietitians work in community and public-health settings, and/or in academia and research. A growing number of dietitians work in the food industry, journalism, sports nutrition, corporate wellness programs, and other non-traditional dietetics settings.