You can use the words "loose weight" as many times as you want, as long as you use them in different phrases.
Key word phrases might say basically the same thing; However, everyone doesn't search using the same phrase, so using the words "loose weight" and phrasing it in as many ways as possible will increase the chance that one of your keyword phrases will match someone's search phrase.
The same might go for different spelling, capitalization, and such depending on the bot settings. Some might ignore case, some might penalize you for using too many similar phrases.
I think it's best to research how the major SE's crawl your site.