A bowel movement or defecation is the passing of stool through the anus. Normally, it occurs anywhere between one to two times a day to three times or more a week. If it occurs more often or less frequently than the norm, then it is often classified as diarrhea or constipation respectively. However, the definition of diarrhea as having more than 3 bowel movements in a day can be misleading. It does not clearly state the nature and quantity of the bowel movement which are characteristic of a disturbance in the processes of gastrointestinal absorption and defecation. Diarrhea is the passing of more than 200 g (solid) / 200 ml (liquid) of stool in three or more bowel movements within a 24 hour period. The stool is not of a normal consistency, usually watery, and often associated with various other symptoms like urgency, flatulence, abdominal cramping/pain and bowel incontinence to some degree.
There are however cases of frequent bowel movements that cannot fit into the classical presentation of diarrhea. While there is no clear clinical definition for this phenomenon, patients will report a change in bowel habit with an increase in the number of bowel movements in a day. Usually there is little to no difference in the consistency or color of the stool – it is still firm but not hard and light to dark brown. In most cases, it is not a sign of any disease but rather an indication of a change in dietary habits, routine, stress levels or even physical exercise. It may also be associated with the use of stimulants like nicotine (tobacco) or caffeine (coffee/tea), especially if there is excessive use within a short period of time.
However, frequent bowel movements may be the first sign of various diseases that causes diarrhea. It may precede full-blown diarrhea, especially in chronic disease, and should be investigated if it is persistent. A temporary change in bowel movement is not uncommon and should not be immediately attributed to any disease process.
What Causes Frequent Bowel Movements?
The frequency of bowel movements are dependent on a number of factors – food intake, liquid and fiber intake, and gastrointestinal motility. The entire process is discussed in detail under defecation where both the voluntary and involuntary component of bowel control is outlined.
Simply, food that is eaten is broken down (digsted) in the gut and nutrients are absorbed into the blood stream where it is processed by the liver. Residual material in the bowels are either not needed by the body or cannot be absorbed by the body like fiber. The body also “dumps” waste materials into the gut through the means of bile and this is eventually passed out with the stool.
Several defecation reflexes control when the sigmoid colon will allow feces to pass into the rectum. This is partly influenced by stretching of the bowel wall, eating food and even abdominal pressure. Filling and stretching of the rectum initiates the relaxation of the anal sphincter (both a voluntary and involuntary component) and defecation occurs.
Food, Fluid and Fiber
Eating larger quantities of food than is the norm for a person will inadvertently affect bowel habit. Moderately larger quantities of stool passed on each bowel movement and more frequent bowel movements may be seen. Changes in stool color, consistency or even odor may be related to the type of foods consumed.
Fluid contributes to the bulk of stool and makes up about 75% of the fecal weight. Read more on feces composition. Large quantities of water can help regulate the frequency of bowel movements in a person who consumes too little fluids and/or is constipated.
Fiber, especially insoluble fiber, adds bulk to the stool by absorbing water and increasing in size. Since fiber cannot be digested and absorbed by the human body, its stays within the gut until it passes out of the bowels. Consuming larger quantities of fiber will change the bowel habit and regulate the frequency.
Gastrointestinal motility is not under voluntary control. It is large controlled by local reflexes and nerve plexus within the gut wall, namely the celiac and mesenteric plexus. However, it receives additional input via various cranial nerves, spinal nerves and the sympathetic trunk. This means that gastrointestinal motility can be influenced by the higher centers, possibly with further input from the endocrine system. Filling of the rectum and relaxation of the internal anal sphincter may be due to exaggerated defecation reflexes exacerbated by the stress response – neural and hormonal. This will contribute to frequent bowel movements.
Stimulants may have a similar effect, either by stimulating nerve pathways or directly irritating the lining of the bowel.
Physical activity helps with regulating bowel activity as is seen with constipation in those with a sedentary lifestyle. While strenuous exercise can cause diarrhea, like in runner’s diarrhea, most of the time physical activity just assists with maintaining a regular bowel habit. This may appear out of the norm or too frequent to a person who is constipated or has irregular bowel movements.