Small intestinal bacterial overgrowth syndrome (SIBO) has not been well studied
yet, nor has a great deal been written about it, but it’s more common than many
people realize. Also referred to as small bowel bacterial overgrowth (SBBO), SIBO
is a condition wherein the small intestine (small bowel) becomes ripe with abnormally
large amounts of bacteria.
Normally, the number of bacteria is highest in the colon (large intestine) and substantially
lower in the small intestine. As well, the types of bacteria within the small intestine
(the part of the gastrointestinal tract connecting the stomach to the colon) are
different than those within the colon. However with SIBO, the types and amount of
bacteria resemble colonic bacteria rather than those normally present in the small
High concentrations of bacteria in the colon are necessary for optimum health. In
the small intestine, however, high numbers of bacteria interfere with proper nutrition,
and are connected to various other health problems.
How SIBO works against your good health
A healthy small intestine is required for the proper absorption of nutrients; this
means that desirable levels of bacteria are necessary. But when the small intestine
becomes overgrown with bacteria they begin to compete for nutrients, which results
in the production of by-products that can irritate, inflame, and damage the absorptive
surface of the small intestine.
This damage disrupts the absorption of carbohydrates (sugars) fats, fat-soluble
vitamins, and sometimes proteins, leading to malabsorption and malnourishment. In
the process, a lot of gas is produced, resulting in
bloating, flatulence, gassiness, diarrhea, and a great deal of discomfort.
In severe SIBO cases, weight loss is a factor as the bacteria consume most of the
calories leaving little left over for the host.
Common SIBO symptoms
While symptoms tend to be patterned and chronic, they may also come and go; sometimes
they persist for years before signs of malnutrition present. Severity depends upon
the type of bacteria present as well as the extent of overgrowth, and not all of
the symptoms occur for everyone:
bloating and/or belching soon after eating
- Abdominal cramps, discomfort, and pain
- Bulky, floating, frothy, loose, smelly stools
- Loud rumbling noises in the belly soon after eating
- Nausea and vomiting, especially after meals
- Weight loss
Rather than diarrhea, some SIBO sufferers complain of chronic constipation. Others
report symptoms seemingly unrelated to the gastrointestinal tract, such as body
aches and/or fatigue.
Other problems created by SIBO1
When the overgrowth is severe and prolonged, damage to the absorptive surface of
the small intestine can interfere with the absorption of fats, proteins, sugars,
- Poor digestion of fats results in weight loss and steatorrhea (stools that have
excess amounts of fat, and characterized by a foul smell, and a loose, floating,
and greasy appearance).
- Poor digestion of proteins results in increased susceptibility to infections and
hair and weight loss.
- Poor digestion of sugars – Symptoms vary in intensity depending on sugar consumption:
belching, bloating, cramping, gas, and watery diarrhea.
- Vitamin B12 deficiency may result from bacteria utilizing B12, and rendering it
unavailable for absorption: causes anemia.
- Vitamin A deficiency may occur resulting in night blindness, sensitivity to sunlight,
and other vision problems as well as skin changes.
- Vitamin D deficiency may lead to bone softening and joint pain.
- Vitamin E deficiency may lead to nervous system problems.
- Calcium / Magnesium deficiency may cause problems with tetany (painful intermittent
muscle cramping that occurs in calves, fingers, and/or toes).
SIBO causes and risk factors
What causes SIBO? Risk factors tend to fall into three categories:
1) Problems with motion/muscular activity;
2) Immune system disorders; and
3) Conditions that encourage colonic bacteria to move into the small intestine.
Healthy muscular activity flowing through the small intestine is important not only
for the proper digestion
of food, but it also clears out bacteria and controls bacterial count in
the small intestine. Muscular interference allows bacteria to remain in the intestine
longer and multiply. Bacteria may also be allowed to spread backwards from the colon
into the small intestine when muscular activity is disrupted.
SIBO can develop as a result of any condition disrupting motility/muscular activity
throughout the small intestine:
damages nerves that control intestinal muscles.
- Muscular and neurologic diseases can alter activity of intestinal muscles.
- Obstruction, partial or intermittent, of the small intestine interferes with food
transport and bacteria through the small intestine. Causes of obstruction leading
to SIBO include surgical scarring and
- Out-pouchings of the small intestine; fistulae and diverticuli are anatomical problems
that allow bacteria to multiply.
- Scleroderma damages the intestinal muscles directly; it slows the bowel leading
to an increase in bacteria.
- Surgery – Bacterial overgrowth can result following duodenum and/or stomach surgery.
Disorders of the immune system can foster bacterial overgrowth.3 Chronic
pancreatitis, inflammation of the pancreas, inherited immunodeficiency conditions,
and the use of immunosuppressant medications to treat various conditions can be
linked to SIBO.
Conditions that cause colonic bacteria to enter the small intestine are also linked
to SIBO.4 Diseases of the ileum (i.e.
Crohn’s disease) may require removal of a patient’s ileocecal valve, which
connects the small and large bowel, and an increased reflux of bacteria into the
small bowel may result. Following bariatric surgery, there may be an increase in
the bacterial load of the small bowel. Use of proton pump inhibitor medications
decreases stomach acid, and can also lead to bacterial overgrowth.
SIBO can develop when food remains in the stomach too long. This state of stagnation
disrupts gut flora balance, and causes bacterial overgrowth from fermentation, which
can result in SIBO.
Patients on TPN (total parenteral nutrition) – intravenous feeding for malnourishment
– are at increased risk for developing SBBO.
Additionally, consuming large
amounts of sugars (which bacteria feed on) can encourage opportunistic bacteria
to relocate from the colon to the small intestine; there they will thrive, but you
The IBS-SIBO connection
There is much speculation regarding a possible relationship between SIBO and
irritable bowel syndrome (IBS). The similarity between IBS and SIBO symptoms
has led researchers to suggest that SIBO may be responsible for the symptoms experienced
by some IBS patients. IBS is difficult to diagnose and treat, and diagnosis is based
on symptoms and testing to rule out other illnesses rather than anything definitive.
Though research is only in the preliminary stages, scientists have noticed that
significantly more IBS patients experience abnormal hydrogen breath test (HBT) results
than unaffected people. In addition, many patients report a significant decrease
in IBS symptoms after being treated with specific antibiotics.
Diagnosing SIBO – the hydrogen breath test (HBT)
Patients must fast for twelve hours prior to testing. On test day, they’re given
a (pleasant-tasting) carbohydrate syrup solution such as glucose, lactulose, or
sucrose to drink, and then asked to breathe into a balloon-type device every fifteen
minutes over a two-hour period.
Bacteria feed off carbohydrates, emitting gases as by-products absorbed into the
blood stream and released via the lungs. The test assesses the presence of gas in
breath. In a healthy individual, hydrogen or methane wouldn’t be present until two
hours after swallowing the solution. A positive gas result prior to two hours after
swallowing the sugar solution is evidence of bacteria higher up in the digestive
tract, at the level of the small intestine.
HBT testing for SIBO has several drawbacks:5
- Other conditions such as celiac sprue and pancreatic insufficiency can produce abnormal
breath test results.
- Individuals with
slow transit would prolong testing by several hours.
disease of the small intestine, small intestine strictures, or other anatomical
abnormalities can cause bacterial overgrowth, and produce similar symptoms.
The one definitive way to determine whether symptoms are SIBO-related is to treat
and eliminate harmful bacteria. If symptoms disappear, then SIBO has likely been
responsible for the previous symptoms.
Treatment for SIBO
For less severe SIBO cases, some patients find a change in diet helpful. A SIBO
diet requires restricting dietary carbohydrates and increasing fats. In order to
maximum the potential health benefits of a low carbs/high fat diet, a dietitian
ought to be consulted.
As the body heals, the intestine may have difficulty digesting sugars, making the
minerals and vitamins essential. Additionally, some health care providers
recommend B12 injections and iron supplementation.
A variety of antibiotics are also sometimes prescribed to treat SIBO:
- Augmentin (Amoxicillin™)
- Ciprofloxacin (Cipro™)
- Gentamicin (Garamycin™, Gentacidin™)
- Levofloxacin (Levaquin™)
- Levofloxacin (Levaquin™) combined with Metronidazole (Flagyl™)
- Metronidazole (Flagyl™)
- Rifaximin (Xifaxan™)
Many health care providers recommend standard doses of antibiotics for one to two
But there are certain drawbacks to antibiotic use. While treatment is often very
effective, it doesn’t address the underlying disease causing SIBO. Symptoms often
recur once a course of treatment has been completed, which necessitates prolonged
and/or repeated treatment.
Though rarely dangerous, there are sometimes side effects such as diarrhea, nausea,
and vomiting. Fungal infections
of the digestive tract, mouth, and vagina are common because antibiotics
destroy the good bacteria as well as the bad. Another disadvantage is that antibiotic-resistant
bacteria may begin to emerge.
For these reasons, one treatment option is to prescribe a short course of antibiotics
to begin treatment, followed by probiotic use over the long term.
Probiotics are live bacteria, the most common of which are lactobacilli
and bifidobacteria. A good treatment option for some bacterial overgrowth cases,
probiotics replenish the gut’s good bacteria. Certain organic yogurts contain a
variety of healthy living bacterial species as well.
Even after bacterial overgrowth has been successfully treated, damaged tissue can
take six months or more to heal. Known for their healing properties, probiotics
may be helpful throughout SIBO treatment.6 Be sure to use probiotics
in moderation as high dosages can sometimes trigger diarrhea.
Probiotics are used alone, in combination with antibiotics, and/or for long-term
SIBO and links to other diseases
- In 2009, the Journal of Clinical Gastroenterology reported that recent studies suggest
SIBO as a likely cause for non-responsive celiac disease.7
- A large number of people who suffer from rosacea also have SIBO. When treated for
SIBO, many patients reported that the rosacea disappeared.8
- Research has shown that twenty to forty percent of
diabetic patients who suffer with chronic diarrhea do so because they also have
Small intestinal bacterial overgrowth syndrome (SIBO) is thought to be an underlying
root cause of – or at least is linked to – various frustrating and perplexing illnesses.
A good theory since bacterial overgrowth can wreak a great deal of havoc on one’s
So if you suffer from abdominal pain, bloating, gas, and diarrhea, it makes good
sense to schedule an HBT test to check for SIBO. Though testing is not an exact
science at this point in time, antibiotic and
probiotic treatment is inexpensive, relatively simple, and quite often extremely