Sweet Baby Grammar Jesus cries every time you use the word “supposably” and so do I. The word is “supposedly.” “Supposably” actually does mean “capable of being supposed or conjectured,” but that is not the way people tend to use it, and it is not the way you used it in your question. You used it to mean “purportedly” or “allegedly.” Walk on the safe side of the street, people. Use “supposedly.” Trust me.
NOTE: May 2011 – The New York Times article “Is Sugar Toxic?” by Gary Taubes is an excellent article to read as well.