depends from what country the traffic is coming in from and if they are in buy mode.
Have you considered creating a section on your site that you reveiw 3 best proteins, 3 best creatine, 3 best weightloss suppliments etc and link to bodybuilding.com aff program?
http://www.bodybuilding.com/store/index.html dont see the aff program but i thought i saw it in the past…
Also, visitors may not be seeking to buy anything hence low conversion. I think a peel add on the corner that takes them to a section on your site that recomends products might be one way of doing it. Also you might want to mention that they can buy suppliments cheaper online than at a store….
just ideas…