So I stumbled on this paper earlier today while doing some literature review at work (unfortunately not for anything beer related).
Effects of brewer's yeast cell wall on constipation and defecation in experimentally constipated rats. (Lino et al., 2001)
In a nut shell they gave rats a large dose of loperimide (Imodium) to constipate them then fed them either brewers yeast cell wall, a non-fiber diet (negative control), or a high cellulose diet (which should cause a significant laxative effect). They then measured how much the rats pooped and found that those who had the brewers yeast cell wall in their diet pooped significantly more!!!
Finally (at least as of 2001) science might make use of the same effect that every homebrew drinker has known about since their first brew!