That's a great niche for a website, people are most concerned about their body and health, it is ongoing hot topic now so there is no problem with your website's niche but be sure to create quality content on the site because content is like a fuel that drives your site, if people like what you offer to them then they will surely come in search of you, so about this competitor yours, royalweight loss clicnic seems to be a well established site so its not gonna be easy to overtake this site. I suggest you to hire a professional service to work on your site's SEO and also be sure to keep track of your enemy.