Degree

Without degree certificates, it won't be possible to attend the counselling. You need to have your documents with you at the time of counselling.

You need to go for a Bachelor's degree from an accredited school of dietetics. You can go for courses like B.Sc in Clinical Nutrition, B.Sc in Nutrition and Dietetics, B.Sc in Food Science and Nutrition, B.Sc in Applied Nutrition, B.Sc in Dietetics and B.Sc in Home Science (Nutrition and Food Science specialisation).

If you have done your B.Ed from a college or a private university which is in the list of UGC approved universities then there shall be no problem in applying with this degree. NCTE also is the approving agency of Teachers Training Courses. Find out whether your university is approved by UGC and NCTE or not. You can share the name here as well.

Minimum time to complete is 2 year and maximum you can take 4 year to do the courses.

The B.Ed course offered is in Distance/Correspondence mode.
For details refer the link: https://www.shiksha.com/teaching-education/course/b-ed-course-annamalai-university-distance-education-tamil-nadu-tamil-nadu-other-68301

Diploma course is very useful. You get more technical knowledge in Diploma but again it's not degree. The kind of salary you will get on diploma basis it will be in the range of 15-20k.
And the salary you will get after degree will be obviously more than Diploma.
Again if you are thinking of doing a Diploma and the degree then risk is on the Diploma marks you get.

Just visit the website www.djsce.ac.in and keep a check on the notices uploaded by the college for direct 2nd year applications. From dates of application to cutoffs everything will be put up there. Constantly keep a check there.