Healthy is Sexy is an EPUB format, which is an ebook standard.
This information might be helpful:
EPUB files can be opened in most eBook readers, but the file has to be converted before usable on the Kindle.
iPhone and Android apps exist that allow viewing of EPUB files. There is even a Firefox Add-on (EPUBReader) and Chrome app (Simple EPUB Reader) that allow you to read EPUB files in the browser just like other documents.
However the iBooks app for iPhones that can be downloaded for free