1) Dietitian 2) Nutritionist 3) Specialiser 4) Specialist 5) Specializer 1) Dietitian 2) Nutritionist 
A nonmedically qualified person who specialises in the art and science of dietetics - the study of food and its nutritional properties. Dieticians give advice on the design of special diets for well and ill patients. ... (16 Dec 1997) ... 
[n] - a specialist in the study of nutrition
A person trained to give advice on diet during illness and using diet to manage symptoms.
dietitian noun a specialist in the study of nutrition
Someone trained in nutrition and diet planning.