為何大便時出現有 (好像公仔麵附加麻油) 油 ?

可能是大便有過多油質。
History--
Any recent intake of excessive fatty meal?
Does this occur frequently before?
Any blood in the stool?

Investigation:
Check stool routine in lab. for fat gobules
ultrasound of liver,gallbladder and pancreas---
these are the major organs involved in fat digestion
may need investigation of the intestine if there is blood in the stool as well
or stool occult blood positive.
Check also complete blood picture and liver function tests.
大便有過多油質:Steatorrheasee definition at wikipedia and possible causes:
Steatorrhea (or steatorrhoea) is the formation of bulky, grey or light colored stools. Stools may also float and have an oily appearance. There is increased fat excretion, which can be objectivated by determining the fecal fat levels. While definitions have not been standardised, fat excretion in faeces in excess of 0.3 (g/kg)/day is considered indicative of steatorrhea.
Seen in:

malabsorption, e.g. in inflammatory bowel disease, celiac disease, and abetalipoproteinemia
exocrine pancreatic insufficiency
chronic pancreatitis
choledocholithiasis (obstruction of the bile duct by a gallstone)
pancreatic cancer (if it obstructs biliary outflow)
primary sclerosing cholangitis
bacterial overgrowth
Short bowel syndrome
Cystic fibrosis

假如有進食過含脂肪成份的食物，經身體分解後未完全被吸收，是會排出體外的