mannito/lactulose test or PEG
There are other possibilities, like low stomach acid, low enzymes, H. Pylori
, ammonia toxicity in
the G/I system, Candida, kidney and/liver dysfunction,magnesium deficiency and many more, however most of these are inter-connected to each other and to leaky gut as well.
I'm certain that some of the above have not been ruled out, or the testing was inadequate/flawed.