I think that people love to see practical application. If you start your personal plan, keep a journal and daily updates with videos, you could gain a lot of people coming back to your site daily just to see your progress. Your own content, your own youtube videos, will jump start your site for ranking. There are millions of people looking to loose weight every single day and your site could do very will with the right SEO optimization, and marketing.
Keep in mind that, once you get this ball rolling and have people following your success, you're kind of obligated to stick with it. If you are progressing, and you're sharing your progress on your site. Your visitors will want to see do it so they can do as well. So, make your plan, start your journal, create your videos, and share it all on your site. Just remember in doing so to be completely honest and simple.
Good luck and keep us posted