A Registered Dietitian (RD) is a nutrition professional. The RD credential indicates the practitioner has completed an accredited 4-year educational program, 1000 hours of supervised practice, and passed a national board exam. RD's use only scientifically based research methods for disease control and prevention, change of body composition and improvement of athletic performance. Depending on which state you are located in, the word Nutritionist could mean different things. For example, in Texas, anyone (including your next door neighbor) could call themselves a nutritionist. This person may or may not have a degree in nutrition. They could just be teaching from experience which only goes so far.