Small Intestinal Bacterial Overgrowth (SIBO)

What exactly is SIBO?

Small intestinal bacterial overgrowth, or SIBO, is an emerging condition which affects the digestive system, one of the most important systems in body. It is made up of the mouth, esophagus, stomach, small and large intestines, liver, pancreas and gallbladder, it digests food and absorbs nutrients that will be used by the body for growth and repair of cells and tissues.

The digestive tract accomplishes these functions with the help of good bacteria called gut flora or the microbiome. This gut microbiota contains trillions of bacteria that can weigh up to two kilograms. These bacteria are located in the intestines, and not only help in digestion, but also help to produce vitamins such as Vitamin B and Vitamin K. They also protect the gut from harmful microorganisms and other diseases.¹

But just like anything else, too much of something can be a negative. Too much bacteria in the intestines can lead to small intestinal bacterial overgrowth (SIBO), which can, in turn, lead to long-term diarrhea and malabsorption. These two conditions can further lead to unexplained weight loss, malnutrition and even osteoporosis.

Many people develop these conditions and think they have contracted simple infections or indigestion. What they don’t realize is that they may be suffering from SIBO, an overgrowth of intestinal microorganisms that are not only caused by anatomic abnormalities in the gastrointestinal tract, but also lifestyle factors, which are, thankfully, reversible and easily modified.

The medical definition of SIBO is an overgrowth of bacteria exceeding 105 to 106 organisms per milliliter. Normally, there are 103 organisms per milliliter found in the small intestine, and many are Gram-positive organisms.² The type of bacteria also plays a huge role in the development of SIBO signs and symptoms.

For instance, if there are more bacteria that digest bile salts to insoluble compounds, there may be fat malabsorption or bile diarrhea. If there are more bacteria that metabolize carbohydrates and transform them to short-chain fatty acids, gas and bloating may be felt without diarrhea. If there is overgrowth of Gram-negative bacteria such as Klebsiella, toxins may be present that will damage the intestinal lining, which can then interfere with food absorption and can mimic symptoms of inflammatory bowel disease.³

SIBO comes in three types: SIBO brought about by methane-producing bacteria, hydrogen-producing bacteria, a combination of methane-producing and hydrogen producing bacteria.⁴

If SIBO is caused by bacteria that produce hydrogen, it can cause unabsorbed carbohydrates to ferment first before being digested, and can lead to diarrhea. On the other hand, if SIBO is caused by bacteria that produce methane, it can cause constipation.⁵

The small bowel (or small intestine) and SIBO

To understand how SIBO affects our digestive tract, let us first review the anatomy of the gastrointestinal tract.

The small bowel, also known as the small intestine, is a part of the digestive tract that is located between the stomach and large intestines, where most of the food is absorbed. In celiac disease, this is what is damaged by the protein in gluten.⁶

The small bowel is composed of three sections: the duodenum, the jejunum, and the ileum. The duodenum is the first and shortest part of the small intestines, where food is prepared before being absorbed. The jejunum is next and lies between the duodenum and the ileum. This is where nutrients are absorbed from food.⁷

The ileum is the final part of the small intestines and is where Vitamin B12, bile salts and other nutrients are absorbed. It is attached to the large intestine.⁸

The small bowel digests and breaks down proteins, fats and carbohydrates with the help of digestive enzymes from the liver, gallbladder and pancreas. After food is broken down, nutrients are absorbed through the blood vessels of the small intestines.⁹

The small bowel is also where the good bacteria reside. It is the area where the body deals with allergens and passes information about them to the immune system. Normal gut flora carries out many beneficial functions for the body that are related to cell growth, intestinal movements and immunity. It maintains normal digestion of nutrients while also helping to produce micronutrients such as Vitamin K and folate. It helps ferment unabsorbed carbohydrates into short chain fatty acids which can further be used by the body as an energy source. It also helps in the metabolism of medicines such as sulfasalazine.¹⁰

If there is a disturbance in the normal gut flora of the small bowel, there may be widespread inflammation in the intestinal lining. Excess bacterial growth can secrete toxins and enzymes that destroy the mucosal lining of the intestines. With a damaged lining, there is also malabsorption of vitamins and minerals, maldigestion of fats and well as malabsorption of proteins and carbohydrates. Carbohydrate malabsorption is due to the degradation of sugars by excess gut bacteria and damage in the brush border and mucosal lining of the intestines.¹¹

Protein malabsorption can also result from mucosal injury and difficulties in absorption by the intestinal lining. This further results in decreased amino acids and protein absorption. The excess microorganisms can also produce toxins that are harmful to cells and tissues, such as ammonia, alcohol, bacterial peptidoglycans, and D-lactate.¹²

Degradation of carbohydrates by excess bacteria in the gut can increase production of hydrogen, methane, and carbon dioxide, further causing bloating, gas, and abdominal discomfort.¹³

SIBO also causes malabsorption of fats that can further give rise to oxalate stones in the kidney, fatty stools, and fat-soluble vitamin deficiencies. There may also be diarrhea due to the presence of hydroxylated fats and bile acids. Vitamin B12 malabsorption can cause megaloblastic anemia, as well as brain and nerve symptoms such as numbness and poor memory.¹⁴

What causes SIBO?

SIBO can result from a disruption of the normal balance of the gut flora. There are two major ways by which normal gut flora is disturbed: decreased acid secretion of the stomach and problems in intestinal movements. Other factors include abnormalities in the immune function of the gastrointestinal tract and anatomical abnormalities.¹⁵

Gastric acid

Gastric acid is a defensive barrier against harmful microorganisms that enter the gastrointestinal tract through the mouth.¹⁶ This is why decreased acid production, a condition known as hypochlorhydria (achlorhydria), can lead to SIBO.

Bacterial growth can occur after infection with Helicobacter pylori or when the digestive tract undergoes changes associated with aging. It is also interesting to note that SIBO can cause a false positive result for H. pylori testing using urea breath analysis.¹⁷

Gastric acid production can also be diminished when there is long-term use of medicines for gastric hyperacidity, such as proton pump inhibitors, such as omeprazole, esomeprazole and histamine 2-blockers, like ranitidine and famotidine.¹⁸

Motility disorders

The movement of the digestive tract follows a tightly regulated series of movements that direct food from the mouth to the intestines. When a person has not taken any food, a movement called migrating motor complex (MMC) occurs in the digestive tract to remove food debris. Many studies have shown that problems in MMC can also lead to SIBO.¹⁹

Gastroparesis, a condition characterized by delayed gastric emptying, can occur due to uncontrolled diabetes, viral infections, digestive injuries and connective tissue disorders.1 With problems in intestinal movement, SIBO can occur because residual food remains in the digestive tract and is feasted upon by bacteria, which allows them to grow excessively in the intestines.

In patients with liver problems such as cirrhosis, SIBO may also occur because of high pressure in the duodenum and impaired digestive movements. Those with kidney problems may also develop problems in digestive motility because nerves may be affected by high creatinine and blood urea nitrogen levels in the blood.²⁰

What increases the risk of SIBO?

As mentioned, SIBO results from an impairment of host defenses in the digestive tract. This impairment may be due to the suppression of acid production by surgery or by the use of medicines, decreased acid secretion in diseases such as pernicious anemia, immune deficiencies that can give rise to decreased antibody production, and undernutrition.²¹

Here is a summary of the risk factors that can predispose to SIBO:²²

1. Structural or anatomic
2. • Diverticula in the small intestines
   • Small intestine strictures from radiation, medications, or Crohn’s disease
   • Blind loops from surgery
   • Ileocecal valve surgery
   • Proximal and distal bowel fistulas or openings
   • Gastric and stomach surgery
3. Digestive movement disorders
4. • Gastroparesis
   • Small bowel movement problems
   • Celiac disease
   • Long-term intestinal pseudo-obstruction
5. Irritable bowel syndrome (IBS)
6. Metabolic disorders
7. • Diabetes
   • Hypochlorhydria, decreased acidity of the stomach
8. Advanced age
9. Organ dysfunction
10. • Crohn’s disease
    • Liver disease, such as cirrhosis
    • Kidney failure
    • Pancreatitis
    • Low immune resistance
    • Celiac disease
    • Malnutrition
11. Intake of medicines
12. • Long-term use of antibiotics
    • Suppression of gastric acid by proton pump inhibitors and H2-blockers

Other risk factors that can lead to the development of SIBO include old age (75 years and up), long-term diarrhea, decrease in appetite or anorexia, and nausea.²³ SIBO may also occur in children who are younger than two years and in those with irritable bowel syndrome.²⁴

Alcohol and SIBO

Alcohol can affect almost every part of your digestive tract. When it passes through the mouth and throat, it causes irritation. In the stomach, it also causes irritation and inflammation in the stomach lining, a condition known as gastritis. This can lead to formation of ulcers, which can bleed. In the intestines, alcohol causes nutrient malabsorption and problems in intestinal motility. It can also cause pancreatitis and liver inflammation.²⁵

The long-term intake of alcohol can bring about harmful effects in the gastrointestinal tract. Chronic use can alter normal gut flora and bring about damage to liver cells, causing liver failure and cirrhosis. Alcohol-induced SIBO can release toxins from the gastrointestinal tract into the blood to bring about neurobehavioral changes such as anxiety and depression, as well as alcohol cravings.²⁶

A recent study explored the effects of long-term alcohol use on gastrointestinal function with the use of the D-xylose breath test results. It showed that long-term alcohol use causes greater malabsorption than normally found in those with untreated celiac disease. Furthermore, long-term alcohol consumption can also lead to abnormalities in the function of normal gut flora.²⁷ Read more about alcohol-related gut issues.

Malnutrition can arise from too much alcohol consumption. In alcoholics, the body derives energy more on alcohol and less on healthy food. Malnutrition can alter the normal balance of gut flora, and can increase acetic acid levels in the gut. As a result, the increased acetic acid levels inhibit the metabolism of xylose, which further compromises gut function.²⁸

If you have gut issues, it is best to stay away from liqueur (a flavored type of distilled liquor), beer, and sweet wines such as Moscato, some types of Riesling, and some types of rosé, which may be high FODMAP (Fermentable Oligo-, Di-, Monosaccharides And Polyols). The best alcohol for individuals with gut problems include vodka, gin, whiskey and dry red and white wines that are low FODMAP. These drinks may not cause any gut symptoms in small quantities, but you should drink them in moderation because they could cause gut issues if taken in excess.

SIBO symptoms

SIBO can have non-specific symptoms that may include bloating, abdominal pain, abdominal distension, fatigue, and body weakness. How frequent and how serious the symptoms are will depend on the degree of excess bacterial growth. This is why it is difficult to diagnose SIBO and differentiate it from other diseases such as inflammatory bowel disease and lactose intolerance.²⁹

Other symptoms may reflect the underlying cause of SIBO, such as gastric problems in motility, malabsorption, malnutrition, and osteoporosis.³⁰

The SIBO diet

As you might guess from the name, the SIBO diet is designed to treat SIBO, and is one of the most effective ways to do so. It gradually removes foods that give rise to inflammation in the digestive tract so that excessive bacterial overgrowth in the small intestines is prevented.³¹

This diet eliminates sugars, especially FODMAPS, complex, disaccharide and polysaccharide carbohydrates that are difficult to digest. Once these are eliminated, relief may be found from symptoms such as bloating and diarrhea. The low FODMAP diet has been proven to eliminate symptoms of irritable bowel syndrome and significantly improve symptoms of Crohn’s and ulcerative colitis.³²

The SIBO diet eliminates the following sugars:³³

• Fructose, found in fruits, vegetables and honey
• Lactose, found in dairy products
• Fructans, found in gluten products, some fruits, some vegetables and prebiotics
• Galactans, found in legumes
• Polyols, a type of sugar alcohol found in sweeteners

The diet retains foods that are high in fiber and low in sugar. It can also be combined with SIBO treatments such as probiotics and antibiotics.³⁴ While practicing a SIBO diet, you should drink more water to decrease abdominal discomfort and enhance digestion.

Treatment of SIBO

Besides via diet, SIBO is treated by antibiotics that act to directly kill excess bacteria present in the small bowel. It can also be treated by a SIBO diet that will provide the basic nutrients that the body needs while starving the excess gut bacteria. The top antibiotic is Rifaximin, of which 99.6% remains in the gut rather than being absorbed by the bloodstream. The underlying cause of SIBO must also be treated to find relief of symptoms and conditions.³⁵

Below is a list of studies on the efficacy of several treatments for SIBO:

Nutritional deficiencies also need to be addressed. These deficiencies may be supplemented by giving both macronutrients and micronutrients, in the form of omega-3 fatty acids, fat-soluble vitamins, and Vitamins A, D, E and K.³⁶

Supplements for SIBO

Some supplements are also proven to be effective in treating SIBO. These include the following:

Biofilm disruptors

This is composed of supplements that help break down the protective film of bacteria. This film needs to be destroyed so that bacteria can get acted upon by antibiotics. Biofilm disruptors include lactoferrin which is found in goat and cow’s milk, N-acetylcysteine, garlic, green tea, and fibrinolytic enzymes.³⁷

Motility support

As previously discussed, SIBO can be caused by problems in gut motility. Motility or prokinetic supplements such as ginger can be given to promote normal gut movement.³⁸

Probiotics

Though probiotics can treat SIBO, especially when given alongside antibiotics, it should be given with caution, as it may include prebiotic starches that may lead to irritation of the gut. Probiotics such as those containing Lactobacillus, streptococcus and bifidobacterium can also enhance good gut movement.³⁹

Digestive supporters

Supplements such as digestive enzymes, bile salts and other digestive promoters can be helpful with digestive issues associated with SIBO.⁴⁰

Allimed

Allimed is a brand of allicin supplement that has recently become popular in reducing gut inflammation. Allicin is a compound that is extracted from garlic and is responsible for protecting plants from damage and infections. It has numerous health benefits in the treatment of infection, inflammation, high blood cholesterol, hypertension, cancers and many other conditions.⁴¹

Caprylic acid

Caprylic acid is a naturally occurring, medium-chain fatty acid that is often found in coconut oil, palm oil and human milk. It acts to normalize the gastrointestinal tract by promoting a good environment for good gut bacteria. It is able to penetrate intestinal mucosal cells and can stop the growth of fungi in the gut. The usual dose is 1,000 to 2,000 mg three times a day with meals for 3-4 months. Do not take this if you have inflammatory bowel diseases such as ulcerative colitis.⁴²

Does SIBO affect histamine intolerance and diamine oxidase?

SIBO is known to trigger inflammation in the gut, which may be due to an abnormal metabolism of histamine, an inflammatory substance. This can cause damage to the intestinal wall.⁴³

Histamine intolerance is a condition that results from abnormal accumulation of histamine due to an impairment in its degradation. It may be due to damage in the epithelial cells of the intestinal lining which produce and store diamine oxidase (DAO), an enzyme which metabolizes histamine and reduces its levels in the blood.⁴⁴

DAO actually decreases inflammation within the gut and is a protective enzyme. When there is decreased DAO production, there is increased histamine absorption, causing histamine to accumulate, further causing inflammation and further damage to the gut wall. With a breach in the gut layer, it is unable to support normal microbial flora and there may be excessive growth of bacteria, further causing SIBO.⁴⁵

Histamine is found in high concentrations on fermented foods such as cheese, wine, beer, processed meat, and uncooked fish or seafood. If you suffer from SIBO, IBS, or IBD, you must decrease the amount of histamine-triggering foods.⁴⁶

SIBO and chronic fatigue

There is recent evidence showing chronic fatigue syndrome often correlates with SIBO.

This is due to microbial imbalances in the gut that can cause irritable bowel syndrome. SIBO in itself can cause fatigue in many ways. Bacterial overgrowth can cause intestinal lining damage which causes malabsorption, malnutrition, and lack of energy. The excess bacteria in the gut can also feed on important vitamins, minerals, and amino acids before the body can absorb them, bringing about a feeling of fatigue and weakness.

One of the vitamins that is malabsorbed in SIBO is Vitamin B12, which is also responsible for nerve function. A deficiency of Vitamin B12 can bring about fatigue.⁴⁷

SIBO in dogs

Can SIBO exist in dogs? Absolutely! It occurs due to ileus, changes in digestion and absorption, malnutrition, and immune deficiency.⁴⁸

In dogs, ileus occurs when normal movement of the intestines is absent. As a result, partially digested food is present and bacteria increases. Ileus is due to a multitude of causes such as intestinal obstruction, pancreatitis, intestinal parasitism, peritonitis, and many others.⁴⁹

When dogs have altered digestion or malabsorption, this can result in malnutrition and further lowers immune resistance, to further promote SIBO. In some cases, SIBO in dogs may have no known cause, especially among puppies.⁵⁰

The most common signs of SIBO in dogs are diarrhea and passing gas. The dog often suffers from long-term and intermittent diarrhea and may fail to gain weight. Diagnosis would involve taking x-rays and stool examinations. An endoscopy may be done to view the upper part of the small intestine. Blood tests may reveal high folate levels and low cobalamin levels, because the excess bacteria creates more folate yet consumes more cobalamin.⁵¹

German Shepherds are the breed of dogs most commonly affected by SIBO. SIBO in dogs is usually treated by antibiotics. The underlying causes should also be treated. For SIBO without a known cause, there may be no treatment, yet it may require dietary modification and supplements to control it long-term.⁵²

Conclusion

SIBO is a condition that brings about excess bacterial growth in the small bowel. Though there are many studies that have highlighted the efficacy of various treatments, more research needs to be done on other factors and alternative treatments that can prevent SIBO.

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