Interesting. I looked it up in Wikipedia (an unimpeachable source, I know) and it generally agrees with the above -- it's supposed to have "minimal" effect on BG. But "minimal" doesn't mean the same as "zero" so I translate that to mean that for some individuals, it can. Which fits with your experience.
In passing, the article also says that it's supposed to have a beneficial effect on the absorption of calcium and possibly magnesium and that it promotes the growth of intestinal bacteria.