Ask around and you'll hear plenty of people say sourdough sits easier with them than other bread. It's a common enough experience that it's worth understanding where it comes from — and being honest about what's established versus what's still being studied.
The fermentation connection
During sourdough's long fermentation, the wild yeast and lactic acid bacteria in the starter get extra time to act on the flour. Some research has looked at how this process can partially break down certain carbohydrates and proteins, including components of gluten, before the dough is even baked. The thinking is that this head start may make the finished bread easier for some people to digest than bread made with a quick commercial-yeast rise.
What this isn't
It's important to be clear: sourdough fermentation does not eliminate gluten, and traditional sourdough is not safe for people with celiac disease or a diagnosed gluten allergy. If you have a medical condition related to gluten or wheat, sourdough is not a substitute for a product that's actually gluten-free, and you should follow guidance from your doctor rather than anecdotal reports.
Our take
We ferment slowly because we think it makes better-tasting, better-textured dough — that's the primary reason. Some people also tell us it sits better with them than other breads. We're glad to hear it, but we'd rather be straightforward than make promises about digestion that aren't ours to make.