CBSE 12th

Yes you can. A number of universities in India offer diploma course in nutrition and dietetics in distance learning mode . Here is a link please go through it :-
Correspondence Certificate Courses in Food and Nutrition http://www.bestindiaedu.com/distance-learning/courses/food-nutrition-certificate.html
But I would recommend you to go for IGNOU. It is a central university with its regional and study centres in almost all parts of India. Follow this link :-
IGNOU - School of Continuing Education (SOCE) - Programmes - Distance - Diploma in Nutrition and Health Education (DNHE) http://www.ignou.ac.in/ignou/aboutignou/school/soce/programmes/detail/239/2
Good luck.

There are graduate level, Postgraduate level, diploma and certification courses available to pursue in the industry. The post-graduate degree awarded is Master of Tourism Administration (MTA), which is a two year full time programme approved by the Ministry of Tourism, Govt. of India. The Indian Institution of Tourism and Travel Management and some universities offer MTA degree in Tourism. A Post graduate degree can be helpful in getting into managerial and administrative positions in the industry. International Air transport Association (IATA), a World Organisation which provides recognised standard in training to travel, tourism and cargo industry, offers certification courses. Several large travel agencies also offer short-term training programmes, and tend to absorb most of the candidates.
The eligibility for admission to Travel and Tourism courses at the undergraduate level is, higher secondary examination pass.At post-graduate level, eligibility is graduation in any field along with a pass in the entrance test followed by group dicussions and interview conducted by the institute. Proficiency in at least one foreign language is preferred. A diploma in public relations or advertising is helpful from the career point of view. It is also possible to gain these qualifications through correspondence courses. Eligibility for certification courses is 10+2

Madan, with PCB, you can go for many other courses apart from MBBS and BDS, like B.Tech Biotech/ food processing, B.Pharm, BPT, BOT, BVT, BSP, B.Sc Nursing etc other than normal B.Sc.
You can also go for these non-Science courses like BBA, BBA-MBA, BBA-LLB, BFA, BFA-MFA, BJMC, B.Design, Fashion design etc.
There are many private institutions/ universities are offering wide range of courses to choose from. They offer quality education to students, with good job placements. Some are even offering good scholarships so as to help financially weak students as well as deserving students get quality education. You can check the websites of universities for more details.
Good luck