Minimum qualification to become a Dietician is a three or four years Bachelor's Degree in related subjects like B.Sc. Home Science, B.Sc. Nutrition or B.E. Food Technology. However if you have not taken these subjects in your graduation you can go for Masters in Nutrition.
Besides you have to obtain a provisional registration certificate from the Medical Council of India and do one year dietetic internship required to become a practicing dietician in India.