Yellow voluminous diarrheal and oily stool that smells unpleasantly is usually a symptom of fat malabsorption (steatorrhea). Fats are normally digested in small intestine with participation of bile and pancreatic digestive enzymes. Therefore, fat impaired absorption accompanies disorders of liver, gallbladder, biliary tract, pancreas and small intestine.
Diseases of gallbladder and biliary tract
Disorders of bile formation and its release into intestine lead fat malabsorption. Bile is irreplaceable in proper dissolution of fat droplets that eases function of pancreatic digestive enzymes. Problems arise in people with their gallbladder removed, who eat large amount of fatty food. Without accumulation i gallbladder bile is drained into the small intestine gradually in small amounts and it is unable to cope with large volumes of fat. Similarly, yellow oily stools occur in patients with gallstones that obstruct the bile duct. Colic pain and jaundice are other present symptoms. Similar effects have local cancers that prevent bile outflow such as gallbladder cancer and bile duct cancer. We should also mention some autoimmune diseases of biliary tract such as primary biliary cirrhosis and primary sclerosing cholangitis.
Diseases of pancreas
This condition is accompanied with change of pancreas gland into fibrotic tissue with drop of production of pancreatic digestive enzymes. Pancreas can be also affected by cystic fibrosis. This illness causes secretion of too thick pancreas juice that accumulates inside pancreatic tissue and causes damage. Pancreatic cancer also causes disruption of fat absorption, because its mass can easily disrupt bile duct or pancreatic duct.
Diseases of the small intestine
Malabsorption of fat may occur in any disease affecting mucosa of small intestine where fat is digested. It may be a chronic untreated celiac disease and Crohn's disease. Disruption of fat absorption can occur after surgical procedures that are associated with removal of part of the intestine. As a very rare cause of fatty diarrhea we can mention Whipple's disease.
Oily and greasy stools can be side effect of medication suppressing fat absorption. These drugs are sometimes prescribed as weight-loss drugs. Their usage should be, however, combined with low-fat diet otherwise they cause oily diarrhea.
When investigating fatty stool occurrence it is appropriate to identify any other present symptoms (abdominal pain, weight loss, jaundice, etc.) and to perform stool examination. Blood tests help us to evaluate levels of bilirubin and liver tests to confirm biliary disorders. Imaging methods are important, especially abdominal ultrasound is irreplaceable in evaluation of biliary system disorders. As more invasive examination of biliary tract and pancreatic duct we can mention ERCP that also helps to remove gallstones from bile duct.