The characteristics of stool (also known as feces) vary a lot from person to person. Even in a single individual, the characteristics of stool may change on different days depending on the changes in the types of food consumed. The properties of stool that vary include the amount of stool passed during a bowel movement, frequency of bowel movements, color of the stool, consistency of the stool, shape of the stool, and odor of the stool.
Despite the wide variation in the characteristics of stool among people, the following features are generally thought to indicate normal stool. Under normal conditions, the stool has a brown color. Various shades of brown are considered to be normal.
- The stool has a soft but firm consistency under normal conditions.
- The shape of normal stool is elongated (like a sausage).
- The normal amount of stool passed per day is less than 200g.
- There is a wide variation in the frequency of bowel movements in people. A frequency of at least 3 times per week, and no more than 3 times per day, is considered normal.
Normal Stool Color
Different shades of brown (and sometimes yellowish-brown) are considered to be the normal color of stools. The brownish color of stool is due to the presence of urobilin and stercobilin pigments. Both urobilin and stercobilin are derived from bilirubin, through the action of bacteria and air within the intestine. In the absence of these pigments, stool appears pale (almost white in color).
Bilirubin is a metabolic byproduct of hemoglobin catabolism. Upon destruction of red blood cells, the hemoglobin pigment is released into the blood. Macrophages present in the liver take up the majority of his free hemoglobin and convert it into bilirubin. The bilirubin pigment is then excreted into the bile, which gets stored in the gallbladder. The bile from the gallbladder is then released into the duodenum (first part of small intestine). The normal color of bile varies from yellow to green.
Read more on bilirubin.
The presence of fatty foods in the small intestine serve as a trigger for the release of bile into the duodenum. The components of the bile help in the emulsification of fats present in the food. This aids the digestion of fats. Some of the bile released into the small intestine gets reabsorbed through the gut wall into the bloodstream. The bile that remains in the intestine gets converted into stercobilin through the action of bacteria present in the gut. The stercobilin pigment is mainly responsible for imparting brown color to the feces.
Abnormal Stool Color
Abnormal changes in the color of the stool could be caused by many factors. Before considering the pathological causes, one must rule out the more mundane causes such as consumption of foods and beverages that are laced with strong colorants or dyes.
Food products may have artificial colors in them to make them more appealing to consumers. This could be a reason for abnormal colored stool in some cases. Also, some foods contain natural pigments that may impart a color to the stool. The following are some of the abnormal colors of stools and their potential causes:
Red colored stool
Consumption of strong artificial food colors, beetroot juice or soup, jelly and concentrated fruit juices can result in red colored stool. Pathological causes of red colored stool include the presence of fresh blood in the stool (a condition referred to as hematochezia). The cause of fresh blood in the stool could be anal fissures, hemorrhoids, or various intra-intestinal factors.
Orange colored stool
Orange colored stool can also be caused by consumption of strong food colorants, and certain foods and beverages. In these situations, avoiding such foods for a few days would restore the normal stool color. Blood in the stool, when mixed with other pigments, could also impart an orange color to the stool.
Yellow colored stool
Consumption of certain foods and beverages with strong yellow pigments can cause yellow colored stools. Among pathological causes, diarrhea is frequently characterized by yellow colored stools. The yellow color of stool in diarrhea is due to the presence of bilirubin pigment in the stool. Under normal circumstances, bilirubin in the intestine is converted into brown colored stercobilin by the action of gut flora.
However, in diarrheal diseases, stool passes through the intestine at a higher rate, which prevents the conversion of bilirubin into stercobilin. Absence of gallbladder could also cause the stool to turn yellow due to dumping of bile from the liver into the intestine.
Other pathological causes of yellow colored stool include cholestasis, liver diseases, gallbladder diseases, pancreatic diseases, and abdominal tumors that may compress the bile duct. Medicines that affect bile production may also be responsible for yellow colored stool.
Green colored stool
Physiological causes of green colored stool include consumption of green leafy vegetables, iron-rich foods, laxatives, algae, and nutritional supplements. Pathological causes of green colored stool include diarrhea, gastroesophageal reflux disease, thyrotoxicosis, impaired gut innervation, and Crohn’s disease. Surgical removal of terminal ileum is also associated with green colored stools. The greenish hue in the stool is mostly due to the presence of bile.
Pale stools are caused by the absence of bilirubin and its derivatives in the intestine. Obstruction of the biliary duct, liver diseases, pancreatic cancer, intestinal infections and inflammatory conditions can cause pale stools.
Read more on pale bowel movements.
Normal vs Abnormal Stool Shape and Consistency
Under normal circumstances, about 70-75% of feces is composed of water (by weight). Rest of the weight is solid matter, which varies in composition. The composition and consistency of stool is determined by dietary and lifestyle factors, medications, and pathological factors. Bristol stool chart is a medical aid that helps in the characterization of both normal and abnormal stool based on shape and consistency. In the Bristol stool chart, stool is classified into seven different groups.
- Type 1: Hard, dry, lumpy stools that are hard to pass
- Type 2: Sausage-shaped, lumpy stools
- Type 3: Sausage-shaped stool with a cracked surface
- Type 4: Sausage-shaped stool that is soft and smooth
- Type 5: Soft blobs of stool that are passed out easily
- Type 6: Fluffy or mushy stool with ragged edges
- Type 7: Watery stool with no solid pieces
Normal vs Abnormal Quantity and Frequency of Stool
There is a lot of individual variation in the daily and weekly frequency of bowel movements and the amount of stool passed during each bowel movement. Abnormalities in the frequency of bowel movements and the amount of stools passed during a bowel movement can be classified into two groups: diarrhea and constipation.
Read more on small volume bowel movement.
Constipation is defined as a frequency of less than three bowel movements in a week. Straining during defecation and difficulty in passing stools are typical features of constipation. On the other hand, diarrhea is defined as having more than three bowel movements in a day. More than 200g (or 200mL) of stool may be passed in a day by a person suffering from diarrhea.
Based on these definitions of diarrhea and constipation, a normal frequency of bowel movements is at least three times per week (no more than three times per day), and the normal amount of stool passed during a bowel movement is no more than 200g.