A dietitian (also 'dietician', though 'dietitian' is used consistently by professionals) is an expert in food and nutrition.
Dietitians help promote good health through proper eating. They also supervise the preparation and service of food, develop modified diets, participate in research, and educate individuals and groups on good nutritional habits. Artificial nutritional provision to patients not able for normal oral intake and dietary modification to address medical issues involving dietary intake is a major part of dietetics. The goals of the dietary department are to provide medical nutritional intervention, obtain, prepare, and serve flavorsome, attractive, and nutritious food to patients, family members, and health care providers.