found: OED online, Aug. 10, 2015:nutritionist (An expert in or student of (esp. human) nutrients and nutrition) dietician (see dietist) dietist (One who professes or practises dietetics or some theory of diet.)
found: Merriam Webster online, Aug. 10, 2015:nutritionist (a person whose job is to give advice on how food affects your health) dietitian (a person whose job is to give people advice about what to eat in order to be healthy; variant: dietician)
found: BLS Occupational outlook handbook online, Aug. 10, 2015:Dietitians and Nutritionists (Dietitians and nutritionists are experts in food and nutrition. They advise people on what to eat in order to lead a healthy lifestyle or achieve a specific health-related goal.)
found: MeSH, Aug. 10, 2015:Nutritionist (Persons specially trained in nutrition sciences; entry terms: Dieticians; Dietitians)