[stevenkovar]

A common argument for vinegar is that the microbiome in your gut needs bacteria to feed on nutrients your body doesn't absorb easily (fiber) and that vinegar (usually apple cider vinegar) helps the bacteria in your gut digest this fiber (via fermentation).

Basically, vinegar makes your stomach bacteria happy, which makes your greater digestive tract happy in turn.

I don't know how true this is, but I do know greater amounts of research are being done on the microbiome as of late, and we're learning just how important it is for our overall health. So it wouldn't surprise me if this explanation is close to correct.