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Symptoms and Signs of SIBO (Small Intestinal Bacterial Overgrowth)

Doctor's Notes on SIBO (Small Intestinal Bacterial Overgrowth) Symptoms, Diet, Natural/Antibiotic Treatments, and IBS

SIBO (small intestinal bacterial overgrowth) signs and symptoms include flatulence (excess gas), abdominal bloating or distention, diarrhea and abdominal pain. Some patients have chronic constipation, body aches and/or fatigue. Some patients appear to be malnourished.

Abnormally large populations of bacteria digesting food in the intestine produce enough gas so that it can accumulate in the abdomen and cause SIBO disease. These bacteria also convert foods like sugars and carbohydrates in large amounts that are irritating or toxic to cells of the intestinal tract. At the same time, they compete with the patient for food. Partial or intermittent obstruction of the small intestine can encourage the growth of these bacteria; other conditions such as neurologic and muscular diseases that slow the gastrointestinal motility so that bacterial overgrowth is not swept away. Diverticuli (pouches in the GI small intestine mucosa) allow large bacterial populations to thrive as the populations are not swept away even with normal GI motility.

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Medically Reviewed on 3/11/2019

SIBO (Small Intestinal Bacterial Overgrowth) Symptoms, Diet, Natural/Antibiotic Treatments, and IBS Symptoms

The symptoms of SIBO include

A small number of patients with SIBO have chronic constipation rather than diarrhea. Patients with SIBO sometimes also report symptoms that are unrelated to the gastrointestinal tract, such as body aches or fatigue. The reason for these symptoms is unclear. The symptoms of SIBO tend to be chronic. A typical patient with SIBO can experience symptoms that fluctuate in intensity over months, years, or even decades before the diagnosis is made.

How does small intestinal bacterial overgrowth cause symptoms?

When bacteria digest food in the intestine, they produce gas. The gas can accumulate in the abdomen giving rise to abdominal bloating or distension. Distension can cause abdominal pain. The increased amounts of gas are passed as flatus (flatulence or farts). The bacteria also probably convert foods including sugar and carbohydrates into substances that are irritating or toxic to the cells of the inner lining of the small intestine and colon. These irritating substances produce diarrhea (by causing secretion of water into the intestine). There also is some evidence that the production of one type of gas by the bacteria, methane, causes constipation.

Bacteria in the small intestine, when present in large numbers, can compete with the human host for the food that is eaten. This can lead to malnutrition with vitamin and mineral deficiencies. In advanced cases of SIBO, the bacteria use up enough food that there are insufficient calories for the host, thereby leading to weight loss.

SIBO (Small Intestinal Bacterial Overgrowth) Symptoms, Diet, Natural/Antibiotic Treatments, and IBS Causes

The gastrointestinal tract is a continuous muscular tube through which digesting food is transported on its way to the colon. The coordinated activity of the muscles of the stomach and small intestine propels the food from the stomach, through the small intestine, and into the colon. Even when there is no food in the small intestine, muscular activity sweeps through the small intestine from the stomach to the colon.

The muscular activity that sweeps through the small intestine is important for the digestion of food, but it also is important because it sweeps bacteria out of the small intestine and thereby limits the numbers of bacteria in the small intestine. Anything that interferes with the progression of normal muscular activity through the small intestine can result in SIBO. Any condition that interferes with muscular activity in the small intestine allows bacteria to stay longer and multiply in the small intestine. The lack of muscular activity also allows bacteria to spread backward from the colon and into the small intestine.

Many conditions are associated with SIBO. A few are common.

  • Neurologic and muscular diseases can alter the normal activity of the intestinal muscles. Diabetes mellitus damages the nerves that control the intestinal muscles. Scleroderma damages the intestinal muscles directly. In both cases, abnormal muscular activity in the small intestine allows SIBO to develop.
  • Partial or intermittent obstruction of the small intestine interferes with the transport of food and bacteria through the small intestine and can result in SIBO. Causes of obstruction leading to SIBO include adhesions (scarring) from previous surgery and Crohn's disease.
  • Diverticuli (outpouchings) of the small intestine where bacteria can live and multiply and are not swept away by the intestinal activity. Diverticuli of the colon, an extremely common condition is not associated with SIBO.

There are three situations in which abnormally increased amounts of gas are produced in the colon.

  1. Malabsorption of sugars and carbohydrates: Reduced digestion or absorption by the small intestine allows increased amounts of sugar and carbohydrate to reach the colon where greater amounts of gas are produced. The most common example of malabsorption leading to increased production of gas is lactose (milk sugar) intolerance. Lactose intolerance is due to a genetic lack of an enzyme in the lining of the small intestine that digests lactose, the sugar in milk. Other causes of malabsorption that can lead to excessive production of gas include: (1) genetically-determined malabsorption of other sugars such as sucrose, sorbitol, and fructose; (2) diseases of the pancreas that result in inadequate production of pancreatic enzymes that are necessary for digesting sugars and carbohydrates in the small intestine; and (3) diseases of the lining of the small intestine (for example, celiac disease) that reduce the sugar and carbohydrate-digesting enzymes in the lining and reduce absorption of sugars and carbohydrates in the body.
  2. Rapid intestinal transit: Normal digestion and absorption of sugars and carbohydrates requires time. If food passes through the small intestine too rapidly, there is not enough time for digestion and absorption to be completed, and more sugar and carbohydrate reach the colon. The best example of rapid intestinal transit is in individuals who have had a large portion of their small intestine removed surgically. There are also a small number of individuals with intact small intestine who, for unexplained reasons, have abnormally rapid transit through the small intestine.
  3. Small intestinal bacterial overgrowth (SIBO): In patients with SIBO, large numbers of gas-producing bacteria (normally present in the colon) are present in the small intestine. The abundant bacteria in the small intestine compete with the small intestine for the digestion of sugars and carbohydrates, but unlike the small intestine, the bacteria produce large amounts of gas.

IBS - Irritable Bowel Syndrome Symptoms, Diet, Treatment Slideshow

IBS - Irritable Bowel Syndrome Symptoms, Diet, Treatment Slideshow

Irritable bowel syndrome (IBS) is a chronic disorder in which the intestines do not work normally. Other names for IBS are spastic colon or functional bowel disease. The consequences of the malfunction of the intestines is abdominal pain that is associated with constipation, diarrhea, or constipation alternating with diarrhea. The disorder affects at least 10% of the population of North America.

Irritable Bowel Syndrome (IBS) : Test Your Medical IQ Quiz

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REFERENCE:

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

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