Most of the brown color of the normal stool is a result of old blood cells being broken down into a substance known as bilirubin and released by the liver through bile production into the intestines. The National Institutes of Health states that light or pale feces may be indicative of a number of diseases or disorders, some which may also cause fatigue.
Liver Disorders
As the liver is responsible for the gathering of bilirubin and releasing it through the bile into the small intestine, liver disorders such as hepatitis and cirrhosis may cause the liver to stop functioning. If the liver cannot produce bile and remove bilirubin from the blood, the stool may turn pale or clay-colored. As bilirubin is not being removed from the bloodstream, the increased blood concentrations of bilirubin may contribute to fatigue, particularly if an infection such as hepatitis is involved.
Bile Duct Obstruction
In order for bile containing bilirubin to be released from the liver, it is first stored in the gallbladder, where it is then released through tubes known as bile ducts into the intestines. If bile ducts are obstructed, the bile cannot travel and feces may become lighter in color. Bile duct obstruction may be caused by trauma, cysts or inflammation of the bile ducts resulting in blockage. Obstruction of the bile ducts may also occur from tumors of the pancreas or other tumors of the biliary system. As bilirubin levels in the blood become elevated, some patients may experience fatigue along with abdominal pain and possible fever.
Gallstones
Gallstones are common occurrences among adults. Gallstones are developed from constituents of bile and may be made of cholesterol or hardened bilirubin. Women are more likely to get gallstones, particularly if they have lost a great deal of weight. Gallstones may range in size from microscopic to as large as a golf ball. When the gallstone gets large, it may block the bile ducts that release the bilirubin-laden bile into the intestines, causing the feces to become pale in color. Other symptoms of gallstones or gallbladder disease may include abdominal fullness and pain, which may spread to the back, along with fever, fatigue and jaundice.
Cancer
Some types of cancer may cause light or pale-colored stool along with fatigue. Pancreatic cancer may cause the stool to become a light yellow color because of a lack of digestive enzymes coming from the pancreas. This may also cause fatigue, as food is not fully digested and nutrients cannot be absorbed, resulting in possible malnutrition. In some cases, the pancreatic cancer may also block the bile duct that enters the intestines very close to the area of the pancreatic duct. Biliary tumors and other cancers that block the location of the bile duct will result in pale or clay-colored stool formation. As with all cancers, fatigue is a common effect, and particularly so if bilirubin levels are elevated.
Medications
Some medications may cause the feces to become light in color. Medications used to treat infectious disease such as isoniazid, used for the treatment of tuberculosis, may induce a condition known as cholestatic jaundice, where bilirubin levels are elevated and may lead to fatigue. Medications given for intestinal conditions such as diarrhea, including bismuth salicylate and kaolin, may cause light stool as they are chalky in appearance. This is particularly true when taken in large doses. The presence of diarrhea may also result in fatigue. Swallowing barium sulfate or receiving a barium enema for a gastrointestinal X-ray exam will also result in white or pale stool, but fatigue is not a likely result of barium ingestion.
