Manipulating Gut flora in vivo I am tasked with designing an in vivo experiment in humans that requires manipulating the gut flora in one sample group to gauge its effect. Please suggest ways of doing this besides administering antibiotics. I am of the view that antibiotics may have unintended consequences and may be unethical; explain any opposing view.

I can't think of any way to start with an intestinal "blank slate", so to speak, except with antibiotics.

Perhaps it's possible to at least partially homogenize/standardize a sample group's biota with probiotics?

If it's ethics you're worried about, perhaps draw experimental subjects from a pool already being treated with antibiotics (although this, I suppose, introduces it's own biases?).