To increase your visitors you can try to market it through email marketing, by answering forums related to fitness and turning the asker into your customer, SEO etc.I suggest you to use the SEV(Search Engine Visibility) from Tucktail.com as they cover many techniques like keyword and suggested topics,submit the site to over 100 search engines,submission to directories,sitemap creation and also provide reports which will eventually improve your website traffic.They also offer email marketing service through which you can send about your website services to many people and get targeted visitors using the opt in and opt out option in email.To get more subscribers you can also announce some competition or free give aways..like you can give books related to fitness tips or diet for free...but on condition basis like the user should avail the email subscription, like the website through social networking sites, spread a good word amongst peers..etc.In this way you can get more subscribers as well as visitors.