This is interesting, i compared my 3 fish foods, and here is what I got.
Aquarian algae wafers - 3.5% fiber
Aquarian shrimp pellets - 6.3% fiber
tetramin flakes - 2.0% fiber
I think for terating a constipated fish, it is best to feed peas or daphnia. I don't have daphnia on hand, so i can't tell you the fiber in there.