First, you will need to do a little bit of research to see which career you would like to pursue. Some of the options for becoming a weight loss expert include nutritionists, licensed dietitians, therapists, life coaches, personal trainers and acupuncturists. Now, how much contact do you want to have with the people you work with? Do you want to develop a close relationship with your patients, like a life coach or therapist would? Or do you want a relationship that is a bit more active, like with a personal trainer or physical therapist? With the latter, you will be able to see the physical changes in your patients as they work for their goals. Either path you choose, you will be helping folks to become excited about making changes in their personal lives.
Now, you will need to do a bit of research to see about the training and licensing for the career fields you're interested in. Some only require you to obtain a certificate, while others will want you to go as high as a master's degree.
You can get in touch with schools and companies to find out about the requirements for the position you're interested in. You can also find out about programs that offer certification in that field. Once you find a school, you can look around for scholarships.