This question stems from curiosity rather than any doubts about our ancestral health approaches.
Background: Water kefir is widely held to be a healthy probiotic drink; even the Weston Price Foundation has good things to say about it.
I've fermented my first batch of water kefir and I'm experiencing a very positive reaction in my GI tract. I'm starting slow because it's powerful, but I would drink more if I were sure I were fully adjusted. Water kefir cultures (aka grains but they aren't) thrive on organic whole sugar--they consume most of it during fermentation--and fresh/dried fruit--frequently added in a secondary fermentation which adds carbonation and flavor.
My question: if I'm thriving on water kefir, and the kefir grains thrive on organic whole sugar, isn't it less scary for me to consume about 4g per day of the organic whole sugar with my coffee as long as my total carbs are 50-75g per day? Won't the probiotics from the kefir happily munch on that little bit of sugar?
I'm no expert, but I think the grains have to interact directly with the sugar in the fermentation medium (water in the jar on your pantry shelf) and not in your gut. I think your body digests the sugar before the water kefir grains can act on it. It takes 24-48 hours to make water kefir from grains on the countertop, I don't think drinking water kefir and then drinking coffee with sugar will cause the coffee sugar to ferment in your stomach.