What Is Diarrhea?

Diarrhea (Greek dia = through, rhein = flowing) means having more than three bowel movements or passing more than 300g of watery stool daily (1).

NOTE: American English spelling is diarrhea, UK English spelling is diarrhoea. Common misspellings for diarrhea: diarea, diahrea, diareah, diarreah.

What Is Not Diarrhea?

Ten diapers a day are usual in a 14 days old infant. Three soft bowel movements a day may be considered normal for adult on a fiber-rich diet. Stool soiling in children who are already toilet trained may be due to defective anus. Stool incontinence or mucus seeping in adults may be due to rectal inflammation, rectal prolapse, hemorrhoids, uncoordinated pelvic floor muscles, or anal muscle or nerve damage (2). In all mentioned cases, bowel movements tend to be of normal volume and consistency.

Occasional single loose stool is not already diarrhea. Unripe fruits, green potatoes, spicy or hot food may all irritate the bowel. Insufficiently cooked or chewed food, a heavy sugary or fatty meal may be hard to digest. Some food combinations, like meat with sugar, may result in a loose stool. Food which is psychically rejected, after ingesting, might flow through the intestine quickly. Caffeine stimulates peristalsis, as can strong emotions, like fear.

Normal Stool

Stool frequency. A newborn passes its first stool in the first two days. During the first month, breast-fed babies usually have 8-10 stools per day, at one month 4 per day, at four months 2 per day, and a child at four years usually has 1 stool per day (7). Three stools per day down to 3 stools per week may be normal for children and adults on solid food.

Stool quantity depends on the amount of ingested food and its fiber content. Two liters of mixed food yields about 200g of stool. The more fiber in the diet, the bulkier the stool.

Stool consistency. A normal stool is semi-solid. Food fibers make stools soft as they tend to bind water. If not enough water is consumed, stools will be hard; on the other hand a lot (up to 20 liters/day) of water consumption will not result in a softer stool, since most of the water is absorbed in the intestine.

The color of the stool in a healthy adult is any shade of brown, or even green. A green stool may originate from green vegetables, fruit juices, or iron supplements. A newborn’s first stool (meconium) is greenish black. A black stool may come from licorice, iron supplements, or Pepto-Bismol. A red stool may originate from beetroot, tomato sauce, red Jelly-O, and so on.

Stool composition: 60-90% of water, the rest are fibers and other undigested substances, bacteria, shed intestinal cells, bile pigments and minerals.

Mechanisms of Diarrhea

Osmotic diarrhea. When a particular nutrient (solute) is not absorbed, it attracts water from blood vessels in the intestinal wall (where it is found in lower concentrations) into the intestinal hollow (with high concentrations). This process is called osmosis and occurs after ingestion of large amounts of unabsorbable solutes (like sorbitol), or when nutrients stay within the intestine, because they can not be digested (in lack of digestive enzymes) or absorbed (in inflammation or surgical resection of a part of intestine).

Secretory diarrhea. Unabsorbed fatty or bile acids trigger water secretion from colonic mucosa; toxins from some bacteria (E. coli, V. cholerae) or some drugs (quinine) have the same effect on the small intestinal mucosa. Secretory diarrhea is watery.

Exudative diarrhea. From ulcerated intestinal mucosa (in shigellosis, amebiasis, ulcerative colitis), the blood, proteins and pus may exudate and appear in the stool. Exudative diarrhea is often of low volume.

Motility diarrhea. In increased gut motility (psychological stress, irritant food, bacterial toxins, laxatives, hyperthyroidism) there is not enough time for adequate water and nutrient absorption, thus resulting in motility diarrhea.

More than one mechanism is usually involved in each diarrheal event.

Diarrheal Stool

The frequency of diarrheal stool may vary from three a day to twenty a day or more in extreme cases. Over 20 liters of water with electrolytes (potassium, sodium, magnesium) may be lost in one day in severe diarrhea. Diarrheal stool may be anything from a clear liquid to soft formed mass.
Water in diarrheal stools originates from food, unabsorbed digestive juices or increased intestinal secretion. White diarrheal stool is from unabsorbed fats (>6g fats/day is abnormal), and yellow stool from lack of bile acids. Green diarrhea is from unabsorbed bile acids. Bloody diarrhea is from ulcerated colonic, or (rarely) small intestinal mucosa. Black colored diarrheal stool is from bleeding from the mouth, nose, throat, lungs, esophagus or stomach, or from antidiarrheal drug Pepto-Bismol. Other components of diarrheal stool: undigested substances, mucus, sugars (like lactose) and microorganisms.

Is Diarrhea Harmful?

In many cases, diarrhea is only an unpleasant event. However, a few liters of body water lost during diarrhea may lead to dehydration within 24 hours, may severely affect metabolism, muscles, nerves, heart, or consciousness, and may cause permanent damage of affected organs. About 2.2 million children die from diarrhea (mostly from dehydration) every year, mostly in countries where medical help is not easily accessible; malnourished children with lowered immunity or chronic diseases are at greatest risk (8). Repeating acute or chronic diarrhea may lead to malnutrition.

Causes of Diarrhea

Main causes of diarrhea are:

  1. Gastrointestinal infections: viruses (mostly Rotavirus), bacteria (like Escherichia coli, Campylobacter, Salmonella, Shigella), parasites (like Giardia, intestinal worms); primarily non-gastrointestinal infections (like measles, tuberculosis)
  2. Inappropriate food (artificial sweeteners, overfeeding)
  3. Psychological factors
  4. Food intolerance: lactose intolerance, celiac disease, food allergies
  5. Medication: antibiotics;
  6. Toxins: pesticides, poisonous plants
  7. Intestinal disease: inflammatory bowel disease, lymphoma
  8. Other abdominal disease: liver, pancreatic, gallbladder disease
  9. Other causes: AIDS, hyperthyroidism, cystic fibrosis, competitive running

Related Articles:

References:

  1. DEFINITION OF DIARRHEA  (cmaj.ca)
  2. STOOL INCONTINENCE  (digestive.niddk.nih.gov)
  3. BILIARY TREE  (healthtalk.com)
  4. FOOD FACTORS INFLUENCING GUT MOTILITY  (biomedcentral.com)
  5. BRAIN-GUT AXIS  (ibs-research-update.org.uk) 
  6. GUT FLORA  (textbookofbacteriology.net)
  7. STOOL FREQUENCY  (cme.med.umich.edu)
  8. DIARRHEA MORTALITY  (rehydrate.org)

Article reviewed by Dr. Greg. Last updated on January 1, 2013