What is a Registered Dietitian (RD) or a Registered Dietitian Nutritionist (RDN) ?
In order to specifically answer this question, it's important to clarify that all dietitians are nutritionists, but not all nutritionists are dietitians. Recently the Academy of Nutrition and Dietetics approved the use of either RD or RDN as the credential for Registered Dietitians, so you may see either behind a Dietitian's name.
There are three steps required to become a nationally credentialed registered dietitian. 1. Earn a bachelor degree with a curriculum accredited by the Academy of Nutrition and Dietetics. 2. Complete an accredited dietetic internship (approximately 6-12 months long). 3. Pass a national examination administered by the Commission on Dietetic Registration.
The process of becoming an RD is lengthy and very competitive. However there are many people who have taken short online courses, or weekend courses in nutrition who call themselves "Nutritionists" or "Certified Clinical Nutritionists". While these individuals may have some knowledge of nutrition, they are not legally licensed to work with disease states and do not always understand how the human body functions on a cellular and biochemical level. When accepting advice from a Nutritionist, ask for educational background, level of degree, specialties and experience.
Dietitians are uniquely qualified to work with your physiology and understand how food choices will affect the body over time at the cellular level. RD's are trained to work in preventing chronic disease states, as well as legally permitted to help treat disease states with nutrition and lifestyle.