It's slang, not really an official term.
There was a post and or a thread about it awhile back, about how they made frozen poop pills to do this easily, instead of having to do it the hard way.
I would probably assert that the weight gain is more likely attributed to the person not having these symptoms anymore:
Quote:
It is used when people have stubborn Clostridium difficile infection in their bowels.
This can cause vomiting, diarrhoea and abdominal pain and cannot always be treated with antibiotics.
So either they're eating the same amount and aren't removing how they were before, or they're eating more because of the lack of symptoms, and or both, etc.
I know I had to change my dietary habits to make my bowel happy.