IBS, Leaky Gut and all tend to be linked in, it seems that digestive tract issues like celiac, yeast overgrowth and all and others caused by autoimmune issues seem to have a higher precence in the ASD community. I'm pretty certain if someone put up a poll, you'd find a good few at least that do have issues.
I have IBS, a gluten sensitivity (supposedly by allergy testing in teen years, everything got worse as I got older, could be Celiac unsure, need testing), and possible lactose intolerance.
Most of my problems happen not long after drinking/eating dairy products and wheat products. I get severe abdominal pain, bloating, gas, chronic diarrhea (not going into further details), headaches, tiredness, generally feeling yucky.
I think there is a research study at Harvard that is starting or already started on looking at digestive tract issues (problems with stomach down through to bowels and such) in autistic children.