It probably falls under their ability to consume things we can't (IE garbage). The effect may be limited even at high dose. (If a person took as much as they did, that person might very well die!)
The thing is that, by default, they should be dead because it DID affect them, if it didn't affect them that would be another story, but if it did affect them they would be shitting so much that they would expell ALL their filling.
>_> so technically there is no reason for them being alive and it would had been better if they didn't since from what they said on previous pages they are ungrateful shitheads.