Hydrogen in the body is not normally a problem. It's such a light gas that it diffuses out the lungs readily, if it's in diatomic form, and your body has good mechanisms for dealing with ionized hydrogen already.
Most people's gut already produces hydrogen (normal levels at or below 16ppm in breath)
It's an interesting question, but I suspect it's not a big deal. H2 is _very_ good at escaping, doesn't really do anything biologically, and our bodies already have ways to get rid of small amounts of gas from various places.
I'm curious if it'd just do the same thing that CO2 does. That might all just be governed by physics and there probably isn't much chemistry involved in that being expelled after it's generated in cells?
I looked up the solubility of H2 in water, and it is _much_ worse than CO2's, so maybe that does suggest it'd at least not use the same mechanisms to escape, not sure.
Most people's gut already produces hydrogen (normal levels at or below 16ppm in breath)