What is Small Intestinal Bacterial Overgrowth?
Small intestinal bacterial overgrowth (SIBO) happens when there are too many bacteria from the colon present in the small intestine. This surge in bacteria can lead to various problems in your gut such as stomach pain, bloating, diarrhea, and in rare cases, difficulties in absorbing nutrients. Usually, the upper part of the small intestine doesn’t have a lot of bacteria due to the stomach acid and movement of food by way of muscle contractions, known as peristalsis.
A few types of bacteria, such as Lactobacilli, enterococci, facultative anaerobes, and gram-positive anaerobes are the primary bacteria present in the small intestine. The amount of bacteria is typically quite low in the jejunum, a part of the small intestine. Bacteria such as Bacteroids, Lactobacillus, Clostridium, and bifidobacteria, which are common in the colon, are seldom found in the upper part of the small intestine.
In the last part of the small intestine known as the terminal ileum, the presence of bacteria is a combination of those found in the upper small intestine (which relies on oxygen) and in the colon (which does not require oxygen). In cases where there’s no gate-like structure called the ileocecal valve that separates the small intestine from the colon, the bacterial composition in the terminal ileum resembles that of the colon.
SIBO can occur when the body’s protective mechanisms, such as the movement of food through the small intestine and the stomach acid, that help control the growth of bacteria are not working effectively. Thanks to improvements in medicine and a better understanding of the condition, SIBO is now recognized by many healthcare practitioners when patients present with general complaints related to the gut.
What Causes Small Intestinal Bacterial Overgrowth?
Small intestinal bacterial overgrowth, often called SIBO, is caused by a mix of factors. These can range from problems with the movement of food through your intestines, changes in your anatomy or immune system, low levels of stomach acid, or due to conditions related metabolism and other systems in the body.
There are a few important ways your body normally prevents bacterial growth in the small intestine. These include stomach acid and bile, the action of the intestines moving food along (peristalsis), enzymes that break down proteins (proteolytic digestive enzymes), a well-functioning ileocecal valve (the ‘doorway’ between the small and large intestines), and a part of your immune system known as secretory IgA. When these protective systems aren’t working properly, you may end up with SIBO.
For example, the acids in your stomach and bile (a fluid made by your liver) kill bacteria and stop them from moving further down your intestines after you’ve eaten something. Proteolytic enzymes work to break down these bacteria in the intestines. If either of these systems aren’t working properly, as with conditions like achlorhydria (low stomach acid levels) or chronic pancreatic insufficiency (when the pancreas doesn’t produce enough digestive enzymes), it can lead to SIBO.
The action of peristalsis – the movement of the intestines pushing food along – and the ileocecal valve, prevent bacteria from moving backwards up the intestines. With certain conditions linked to abnormal intestinal movements like irritable bowel syndrome, or with usage of certain medications such as narcotics, or conditions like hypothyroidism, diabetes, and scleroderma – this may not work as well, leading to SIBO.
Anatomical changes, which can slow the movement of the intestines, can also lead to SIBO. These can include conditions like small intestinal diverticulosis, bowel strictures, aftereffects of surgery like adhesions (bands of scar tissue that can form after surgery), forms of gastric bypass surgery that leave ‘blind’ loops of intestine, and resections or removals of the ileocecal valve.
Finally, our body has a type of immune ‘soldier’, called secretory immunoglobulin Ig A, which helps stop bacteria from growing too much and keeps our intestinal immunity strong. But with immune deficiency disorders, like acquired immune deficiency syndrome (AIDS), combined variable immunodeficiency, and a deficiency in IgA, this protective measure may not work properly, increasing the risk of SIBO.
Risk Factors and Frequency for Small Intestinal Bacterial Overgrowth
It’s hard to determine the exact prevalence of small intestinal bacterial overgrowth, often referred to as SIBO. The most common causes of SIBO, which include irritable bowel syndrome, disturbances in gut movement, and chronic pancreatitis, account for 80 to 90% of all cases. SIBO tends to occur more frequently in women and older people. The risk of developing SIBO increases as one becomes older due to a decrease in stomach acid and slowing of the gut movement. Sometimes, more than one cause for SIBO can be found.
- Exact prevalence of SIBO is hard to determine.
- Most common causes of SIBO are irritable bowel syndrome, disturbances in gut movement, and chronic pancreatitis, which account for 80-90% of all cases.
- SIBO is more frequently seen in women and elderly.
- The risk of SIBO gets higher with age due to a decrease in stomach acid production and slowing down of gut movement.
- In many cases, there can be more than one cause behind SIBO.
Signs and Symptoms of Small Intestinal Bacterial Overgrowth
Small intestinal bacterial overgrowth, also known as SIBO, can cause a range of symptoms. Common indicators include discomfort in the belly, feeling bloated, passing wind more frequently, and having chronic watery diarrhea. Some people can experience weight loss and steatorrhea (which means the presence of excess fat in feces) resulting from the body’s inability to properly absorb fat, especially if the structure of the gut has changed in some way.
Another issue that can arise from SIBO is the deficiency of certain vitamins. For instance, a lack of vitamin B12 can cause weakness, loss of physical coordination (sensory ataxia), and a tingling sensation in the skin (paresthesia). Moreover, severe deficiency of Vitamin D due to inability to absorb nutrients can manifest as numbness around the mouth, a tingly sensation in hands and feet, and muscle cramps due to low calcium levels in the blood.
- Discomfort in the belly
- Feeling bloated
- Passing wind more frequently
- Chronic watery diarrhea
- Weight loss and presence of excess fat in feces
- Weakness
- Loss of physical coordination
- Tingling sensation in the skin
- Numbness around the mouth
- Tingly sensation in hands and feet
- Muscle cramps due to low calcium levels
There are also rare neurological cases related to SIBO known as D-lactic acidosis, which can cause altered mental state, slurred speech, seizures, and loss of physical coordination. This condition is a result of bacterial fermentation of carbohydrates that are not absorbed by the body. It is seen in patients with SIBO who also have a short bowel syndrome or a jejunoileal bypass.
SIBO is also suggested to be associated with nonalcoholic fatty liver disease and hepatic encephalopathy. However, unless severe malnutrition is seen, the physical examination of these patients usually doesn’t reveal much. Occasionally, a sound caused by shaking or tapping the abdomen due to fluid-filled loops can be detected.
Testing for Small Intestinal Bacterial Overgrowth
When a patient shows signs and symptoms that might be related to Small Intestinal Bacterial Overgrowth (SIBO), there’s no one definitive test that can confirm the diagnosis. Usually, your doctor would employ two different tests: a “carbohydrate breath test” or a process where they measure the number of bacteria present in a fluid sample taken from your small intestine, also known as a “jejunal aspirate culture”.
The breath test is relatively quick, inexpensive, and non-invasive — meaning it doesn’t require any surgical procedures or inserting instruments inside your body. The premise of this test is simple. It involves consuming a carbohydrate substrate (either lactulose or glucose) that is then metabolized by the bacteria, creating either hydrogen or methane gas. This gas is absorbed and eventually breathed out by the patient. A sharp increase in hydrogen or methane levels in your breath after consuming the carbohydrate is usually indicative of SIBO. However, it is important to keep in mind that this test can sometimes produce false positive results in patients with a certain condition known as short bowel syndrome and false negatives when the bacterial count is low.
The other test, a jejunal aspirate culture, is more invasive and time-consuming because it requires getting a sample of fluid from your small intestine through a procedure known as an upper endoscopy. It is also more expensive. This test can occasionally result in false results due to uneven bacterial overgrowth or contamination from bacteria in your throat. Other lab results that might indicate SIBO include certain vitamin levels and indications of poor nutrition.
Once SIBO is suspected, your doctor might order additional tests to figure out what might be causing it. They might conduct a physical examination of your stomach and intestines and use endoscopy or imaging technologies to inspect your GI tract for structural anomalies. Testing may be done on a case-by-case basis for other conditions such as abnormal gastrointestinal movement, insufficient pancreas function, or weakened immunity. On some occasions, small bowel biopsies might be performed using endoscopy.
In case you have no known risk factors for SIBO, upper and lower endoscopies might be performed to eliminate other potential causes like atrophic gastritis and Crohn’s disease. If the results are normal, your doctor might turn to imaging studies to rule out other potential complications such as partial blockages, pouches in your colon’s lining (diverticula), abnormal links between organs (fistulas), or other signs of inflammation.
Identifying the cause of SIBO is important, as this condition is commonly associated with other health issues like cirrhosis (liver disease), chronic kidney disease, chronic pancreatitis, and compromised immunity. Abnormal lab results common with SIBO can include macrocytic anemia, deficiencies in vitamin B12, thiamine, and niacin, increased folate and vitamin K levels, and increased fecal fat content. In rare cases, conditions like microcytic anemia or hypoalbuminemia (low levels of a protein called albumin) are reported.
Treatment Options for Small Intestinal Bacterial Overgrowth
Initial treatment of small intestine bacterial overgrowth (SIBO) usually involves antibiotics to get rid of the excessive bacteria and nutritional supplements to replace any deficiencies. A range of antibiotics are used, with rifaximin being the most researched.
For patients who primarily produce hydrogen gas from the bacteria, treatment with rifaximin is usually effective. In patients who primarily produce methane gas, combining two antibiotics, neomycin and rifaximin, works well. Any associated deficiencies in nutrients, like Vitamin B12, iron, thiamine, niacin, and other fat-soluble vitamins, are also treated.
About 45% of patients might have the condition return even after antibiotic treatment. Especially older adults, those who have had their appendix removed, and those frequently using proton pump inhibitors (medication for heartburn) may be prone to reoccurrence. If the condition recurs within three months, another course of antibiotics is given. For reoccurrence beyond three months, antibiotics are given only if a carbohydrate breath test is positive. Recurrent SIBO can be treated either with the same antibiotic used initially or a different one.
For patients who cannot tolerate antibiotics or when antibiotics don’t work after trying twice, an elemental diet can be used. This diet, while not particularly tasty and relatively expensive, has been shown in case studies to alleviate SIBO symptoms in about 80% of patients within two weeks.
Staving off the recurrence of symptoms can be achieved by treating the underlying cause of SIBO. For patients experiencing more than 4 episodes in a year, preventative antibiotic treatment should be used. If severe symptoms continue even after SIBO treatment, it would be necessary to look into inflammatory bowel disease (IBD) as a potential cause. If symptoms persist after two rounds of treatment, the doctor should evaluate for other potential infirmities.
Despite some patients reportedly feeling better, the use of probiotics, a low fermentable oligo, di, and monosaccharide (FODMAP) diet, and statins don’t quite help resolve SIBO all on their own.
What else can Small Intestinal Bacterial Overgrowth be?
When a doctor is trying to diagnose small intestinal bacterial overgrowth (SIBO), they need to also consider other conditions that can cause chronic diarrhea. These include:
- Irritable bowel syndrome (IBS) – this condition involves recurring stomach pain related to bowel movements, and it often comes with changes in stool frequency or appearance.
- Celiac disease – this and SIBO can result in similar symptoms. But with celiac disease, tests will show positive celiac serologies and a negative carbohydrate breath test.
- Crohn’s disease – this and SIBO can both cause patchy inflammation in the mucus lining of the intestines. However, Crohn’s disease can also show up as inflammation all the way through the intestinal wall and granulomas (small inflamed areas) on a biopsy. It can also involve the anus, leading to anal fissures and fistulas (abnormal connections between the anus and other areas of the body).
It’s crucial to examine and rule out these possibilities to make an accurate diagnosis.
What to expect with Small Intestinal Bacterial Overgrowth
The outcome of Small Intestinal Bacterial Overgrowth (SIBO) largely depends on the cause of the condition. Generally, most cases have a positive outcome. Hospital admissions are rarely needed and complications are not common.
Possible Complications When Diagnosed with Small Intestinal Bacterial Overgrowth
Severe and chronic Small Intestinal Bacterial Overgrowth (SIBO) can lead to serious weight loss and malnutrition, causing serious health risks and even death. It’s important to identify SIBO early to treat the poor absorption of nutrients and stop malnutrition from happening. If it isn’t treated, SIBO can cause the intestines to stop working properly.
SIBO is linked to high levels of ammonia production, which can worsen a condition called hepatic encephalopathy in people with pre-existing liver disease. SIBO from conditions like short bowel syndrome or jejunal bypass can cause D-lactic acidosis, a condition that can confuse and imbalance patients from the bacterial breakdown of unabsorbed carbohydrates). The relationship between SIBO and a liver disease called non-alcoholic steatohepatitis isn’t clear yet, and more research is needed.
Common Conditions and Risks Associated With SIBO:
- Significant weight loss
- Severe malnutrition
- Intestinal failure
- Excess ammonia production
- Hepatic encephalopathy in patients with liver disease.
- D-lactic acidosis from short bowel syndrome or jejunal bypass
- Potential link to non-alcoholic steatohepatitis
Preventing Small Intestinal Bacterial Overgrowth
If you have been diagnosed with small intestinal bacterial overgrowth (SIBO), a condition where there’s an excessive amount of bacteria in your small intestine, additional tests are needed. These tests are to identify the cause and establish the right treatment plan to prevent SIBO from happening again. When treating SIBO, it’s also important that other related conditions, such as Crohn’s disease, irritable bowel syndrome, post-radiation enteropathy (a condition caused by radiation therapy), diabetes mellitus, hypothyroidism (an underactive thyroid gland), and scleroderma (a group of autoimmune diseases causing the hardening and tightening of the skin and connective tissues), be effectively managed and under control.
SIBO patients may also benefit from medicines that can help speed up the movement of food through the stomach and intestines (known as prokinetics). However, certain medications like opioids, which slow down the movement of food, and proton pump inhibitors, which reduce the amount of stomach acid, should be avoided as they could worsen the condition.
Surgery might be considered for patients with physical abnormalities in their intestine which cause repeated bouts of SIBO. Research around the long-term use of antibiotics as a preventative measure is limited and using probiotics (beneficial bacteria) alone to prevent the condition might not be effective.
It may also be helpful to follow an elemental diet, a diet composed of easily digestible nutrients, though it might be challenging to stick to. However, despite these difficulties, it could play a role in managing your condition.