This can really be one of many reasons.
This may be a case of unnatural link building. You have 617 links of which 594 are anchored "<a class="clickable title link-pivot" title="See top linking pages that use this anchor text">l arginine". Its best practice to use variations of your keywords when linking in.</a>
<a class="clickable title link-pivot" style="background-color: initial;" title="See top linking pages that use this anchor text">Also the home page looks very very busy. Too many colors and graphics, user interaction might be the issue, maybe people get to your site and leave because of the clutter.</a>
How long has this site been live? was it ranking well in the past (statically) and now its starting to lose ranking (de-indexing)?
Have you checked your webmaster tools?