If you are an M.D. and are doing basic research, apply for a K08.
If you are an M.D. doing clinical research where you interact directly with patients for your research (not just to fulfill your commitment to your department), apply for a K23.
If you are a Ph.D. or a nonboard-eligible M.D., apply for a K01.
If you are a nonbiomedically trained Ph.D. (e.g., mathematics, organic chemistry, etc.) moving into biomedical research, apply for a K25.
The NIDDK does not support the K02 award for more senior scientists. Our overview of all K awards offered by the NIDDK outlines the conditions of each award.