Strange eating habit

Do you have any idea why my 3-year old neutered male tabby is occasionally eating his own feces?

We feed him Whiskas-brand dry food only (both the "meaty selection" from a 25 lb bag as well as the smaller Whiskas Temptations in the small packets). He is strictly an indoor cat; we live in a two-story house and he frequently zips up and down the stairs as well as through the various rooms.
He weighs 13 lbs and has pretty much maintained this weight since we adopted him at the local
SPCA two years ago. In advance, thank you for your insights regarding his strange behavior.

Answer by Kate
well this is strange and i must admit to not having heard of cats doing this. i know dogs sometimes do this, why? No idea i'm afraid. Pica is a condition where cats eat non food items, it is a strange behavior that no one seems to fully understand so perhaps this is a form of pica. the only thing you can try is to spray the feaces with strong smelling substances like lemon juice or euculyptus to try and disade your cat from doing it, but it would mean having to watch out every time your cat uses the litter tray.
Sorry i couldn't be of more help.

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