White uncooked rice like particles in stool may be undigested food, dead worms or mucus flakes. You have not mentioned any altered bowel habit.
So its better to get the stool examination done both routine/microscopy and for parasites.
Have you given any antihelminthic to here few days back. That may cause passage of dead worms in stool. The lack of appetite
which you have noticed may be just an objective finding.
So observe the stool to check whether that white material is still present and also get the stool report done. Consult your physician with the report to find or rule out any abnormality.