If you have questions about food or nutrition, who should you ask? Although some states regulate and license people who call themselves nutritionists, there are no standard legal definitions for this descriptor. Therefore, you cannot always rely on someone who refers to him- or herself as a “nutritionist” for reliable nutrition information. Physicians may not always be the best sources of nutrition information either, because most doctors do not have extensive college coursework in the subject.
To obtain reliable answers to your nutrition, food, and dietary questions, you should consult a registered dietitian (RD). Registered dietitians are college-trained professionals who have extensive knowledge of food, nutrition, and dietetics, the application of nutrition and food information to treat many health-related conditions. The title “registered dietitian” is legally protected, and can only be used by people who have met the minimum academic and professional requirements to qualify for the credential “RD.”
Reference: Nutrition for Healthy Living, by Wendy J. Schiff