The funny thing about the leaky gut truthers is that they aren't wrong about intestinal issues causing systemic inflammation... but they're still totally wrong about what those intestinal issues are and what the ensuing systemic inflammation looks like.
I guess "leaky gut causes autism" is more exciting than "Crohn's can give you eczema and uveitis" :P
https://en.wikipedia.org/wiki/Leaky_gut_syndrome