The frequency of bowel movements varies widely among individuals. Anything from three times a day to three times a week is considered normal frequency for bowel movements. If there are more than three bowel movements in a day, the condition is termed as diarrhea. On the other end of the frequency spectrum, less than three bowel movements in a week is termed as constipation.
In these classifications of abnormal bowel movements, only the frequency of bowel movements is taken into consideration. However, just as important for identification of abnormal bowel movements are other factors, such as the volume of stool in each bowel movement, the shape of stool, and the size of stool. The characteristics of stool also varies based on these criteria annd while some degree of variation may be considered normal, there are also limits where it may then be seen as abnormal.
Passing Too Little Stool
Just as the frequency of bowel movements, the quantity of stools passed in each movement also varies on an individual basis. There is no clear quantitative measure of what constitutes a normal amount of stool in each bowel movement. Sometimes, an individual may feel that the quantity of stool being passed is abnormally low. This is mostly felt in case of constipation, and is often accompanied by a sensation of incomplete defecation.
Under normal circumstances, the urge to defecate is created when the walls of the rectum stretch due to stool coming from the last part of the colon. During the act of defecation, the anal sphincters relax and the stool is pushed out of rectum and anal canal. Emptying of the rectum relaxes the muscles in its walls, and leads to a feeling of having completed the bowel movement. In case of constipation, there is an incomplete emptying of the rectum. This leads to a feeling of incomplete bowel movement.
Small volume bowel movements may also be described based on the shape of stools. Stools may be passed out in small masses that have abnormal shapes and consistency. For example, stools passed out during severe constipation may look like small lumps or balls (technically characterized as type I stools according to Bristol Stool chart). The shape of the stool is determined by how it passes through the rectum and anal canal.
The small balls of nut-shaped stools may result from an obstruction in rectum or anal canal, or as a result of incomplete relaxation of the anal sphincters during the defecation process. The consistency of these nut-shaped stools is mostly hard, which is unlike the soft consistency of normal stools. The hardness of stools may be due to excessive water absorption in the colon.
Read more on weak bowel movements.
Causes of Small Volume Bowel Movements
Small volume bowel movement is caused by a variety of conditions. Constipation is the most common condition associated with the passing of small volumes of stool. The stools passed during constipation are generally hard in consistency. The following are some of the potential causes of small volume bowel movements:
Dietary and lifestyle causes
The consistency, frequency and volume of stools passed by an individual depends a lot on the dietary and lifestyle factors. For example, inadequate water consumption can dry out the stools and make it difficult to defecate. Water constitutes around 60% of the mass of stools in normal conditions. The volume of stool passed can decrease significantly due to inadequate water consumption, even in cases where a person is not actually dehydrated.
Dehydration and decreased volume of stools could also result from excessive alcohol and caffeine consumption. These substances cause dehydration by increasing the frequency of urination. Apart from inadequate water intake, reduced dietary intake of fiber also causes constipation and reduced stool volume. Sedentary lifestyle and lack of regular exercise may also contribute to increased episodes of constipation.
Nervous system causes
The act of defecation depends on muscular contractions of the walls of colon, rectum and anal canal. These muscular contractions are stimulated and coordinated by the nervous system. Therefore, any problem with the nerves can cause problems with defecation. Examples of nervous system abnormalities that can lead to constipation and small stool volume include spinal cord injury, multiple sclerosis, diabetic neuropathy, stroke, and Parkinson’s disease.
The act of defecation depends on the coordinated muscular contractions of the gut wall (especially that of colon, rectum and anal canal). Therefore, any abnormalities in the gut muscles could lead to problems with gut motility, and contribute to constipation and small volume of stools.
Examples of such muscular abnormalities include muscular dystrophy, dyssynergia, anismus, and weak pelvic muscles. In anismus, the muscles of the pelvic floor are not able to relax. Bowel movement is, therefore, prevented. In dyssynergia, the contractions of the gut muscles are not coordinated properly. This causes improper bowel movements.
Obstruction in gut
Small volume of stool could also be a result of an obstruction to the movement of stool through the colon, rectum or anal canal. If a small volume of stool is being passed out, it is likely that the obstruction is not complete. Constipation caused by an obstruction in the gut is also known as obstipation, or obstructive constipation. Conditions that can result in obstipation include narrowing of the gut lumen (strictures), colorectal cancer, colonic polyps, and enlarged prostate gland.
Not all causes of obstruction to the movement of stools in the gut are pathologic. Some physiological conditions could also restrict the movement of stools through the colon and rectum. Pregnancy is an example of one such condition. In this case, colon and rectum are squeezed by the enlargement of uterus. Hormonal changes that occur in pregnancy may also contribute to constipation.
In some cases, there are no evident pathological changes that could be attributed to constipation and small volume stools. In other words, no cause can be identified. These cases are termed as functional disorders. An example is functional constipation caused by a type of irritable bowel syndrome (IBS).
Read more on irritable bowel syndrome.
Gut function is also controlled by psychogenic factors. Emotions such as anxiety, fear, depression, and stress could also cause constipation and small volume of stools.
There are many other conditions associated with constipation and passing of small volumes of stool. These include anal fissures, hyperparathyroidism, and hypothyroidism. Constipation may also be a side-effect of some medicinal drugs.