SIBO - a deeper understanding

Many bacteria in the gut is not always beneficial

This page is for those of you who want to gain a deeper understanding of the subject of SIBO. Perhaps you have, or suspect that you have SIBO, or you work in a field where you meet people with conditions that may be linked to it.

Here we have compiled the basics about SIBO, in the hope of giving more people increased knowledge about the subject.

SIBO: When gut bacteria create health problems

Our body is in a fascinating interaction with bacteria and in our gastrointestinal tract these can play a decisive role in our health. When an imbalance occurs, this can lead to various health problems. One such imbalance that has received increased attention recently is SIBO, or "Small Intestinal Bacterial Overgrowth."

SIBO means abnormally high amounts of bacteria in the small intestine. Since the small intestine does not have the strong protective mucus layer that the large intestine has, overgrowth of bacteria can damage the wall of the small intestine and cause inflammation both in the intestine and in the rest of the body, as well as contribute to the development of chronic diseases and inflammatory conditions such as in muscles and joints.

Chronic stress is considered a major cause of SIBO. In this article, we will present what SIBO is and how health problems can arise in its wake.

The stomach's workhorses should be in the large intestine

The bacteria in our colon can be said to be real workhorses because they digest fibers from our diet that our own cells cannot use and convert these into health-promoting substances such as B and K vitamins.

Bacteria have surface structures that stabilize the outer bacterial cell wall, so-called lipopolysaccharides (LPS) and lipoteichoic acid (LTA) which contribute to maintaining the integrity of the bacteria. However, LPS and LTA are also some of the most powerful inflammation-inducing toxins we know of. Thanks to the colon's wall acting as an impenetrable barrier to LPS and LTA, these toxins cannot reach the body's immune system and cause inflammation from the colon.

This important barrier function comes from the fact that the surface of the large intestine consists of two powerful mucus layers (Figure 1) that keep the bacteria in place inside the intestine and prevent LPS and LTA from passing through the intestinal wall and into the bloodstream (1-5), but still allows salts and water to pass through the colon's two mucus layers and into the bloodstream. Absorption of water and salts into the bloodstream is one of the most important functions of the colon.

The small intestine is permeable to a variety of substances which reach the immune cells and the vascular system

The situation is completely different in the small intestine, as it does not have the same protective mucous wall as the large intestine, but only has a thin and loose superficial mucus layer (Figure 1). Since the small intestine is built to be permeable to a variety of nutrients (amino acids, fatty acids, carbohydrates, vitamins, minerals), a too thick mucus layer would have reduced this permeability. The total surface area for absorption in the small intestine is estimated to be 200 square meters, roughly the size of a tennis court, and it is this large surface area that allows a significant amount of nutrients to be transported from the inside of the gut into the bloodstream. If the small intestine would have had a mucus layer corresponding to that seen in the large intestine, the surface for adequate nutrient absorption would have had to be over 400 square meters, that is, our small intestine would then be over 12 meters instead of 6 meters long.

In the case of overgrowth of bacteria in the small intestine, the bacteria will devour and consume the amino acids, vitamins, minerals and other nutrients that should otherwise have benefitted our body. SIBO can actually be likened to a cuckoo chick that takes care of itself at the expense of others.

Figure 1. The small intestine has a superficial thin and loose mucus layer that allows nutrients to pass through the intestinal wall to the bloodstream, but the mucous is not sufficient to protect the cells of the intestinal wall in case of SIBO.

Figure 2. In the wall of the small intestine, Peyer's plaques (the arrow indicatesindicate the small lymph nodes consisting of immune cells) play an important role in tolerance to substances in our diet, but also in identifying and fighting disease-causing microbes and viruses.

Figure 2. In the wall of the small intestine, Peyer's plaques (the arrow indicate the small lymph nodes consisting of immune cells) play an important role in tolerance to substances in our diet, but also in identifying and fighting disease-causing microbes and viruses.

The immune system of the small intestine plays a central role for our health

The small intestine is an organ that contains a large accumulation of immune cells. It is estimated that up to 70% of the body's immune cells are found along the wall of the small intestine. This high concentration of immune cells is not surprising given the constant exposure to foreign substances from the 1-2 tons of food that we ingest annually; substances that our immune system must either tolerate (our diet) or react to (disease-causing microbes). The immune system in the small intestine is mainly located in small lymph nodes called Peyer's patches (Figure 2).

An example of how the immune system in the small intestine can react to unwanted bacteria is shown by the experiences from oral vaccination against the cholera bacteria. When we drink killed cholera bacteria, these end up on specialized cells in the lining of the small intestine which then transport the cholera antigen from the intestinal contents to the Peyer's plaques. After 2-4 doses of cholera vaccine, our immune system is prepared for a rapid immune response should we be infected by cholera bacteria in the future.

The example of oral vaccination shows how intimately the contents of the small intestine are linked to the immune system and that bacterial products can easily pass through the intestinal mucosa to immunocompetent cells in the wall of the small intestinal and start a reaction that results in an immune response (6).

Unlike the situation with oral vaccination where the intestinal immune cells are exposed to bacteria only on 2-4 vaccination occasions and then return to normal (calm) conditions, the situation is completely different in SIBO, where the intestinal immune cells are constantly activated by LPS and LTA from unwelcome bacteria thriving in the small intestine and thereby causing a chronic inflammation. In SIBO, the immune cells of the small intestine are overactive.

The “gut trolls”

In the oral cavity, we should not have too many unwelcome bacteria (we call them tooth trolls in Sweden) since they may cause gum inflammation due to the lack of a protective barrier. The situation in the small intestine is very similar where the wall of the small intestine also lacks protection against large amounts of bacteria. It is therefore of importance to prevent the overgrowth of unwanted bacteria in the small intestine and three mechanisms are considered relevant in this context:

  • The hydrochloric acid in our stomach, which eliminates bacteria from our food (think of all the bacteria found in, for example, a carrot pulled from the ground).
  • The intestinal peristalsis (motility), which prevents stagnation of food residues that unwelcome bacteria can start to ferment. It is through an active vagus nerve that a normal intestinal peristalsis is obtained.
  • The valve between the large intestine and the small intestine, which is kept tight under normal conditions by an active vagus nerve.

One of our body's most important check valve is sensitive to chronic stress

We can thank the ileo-cecal sphincter, as the valve between the large and small intestines is called, for preventing leakage of bacteria from the large intestine into the small intestine and, thereby, preventing SIBO. Unfortunately, this important check valve has a tendency to leak in case of chronic stress. This valve is kept closed by the vagus nerve, which is active (keeping the valve closed) when we are in a calm state. In case of stress the vagus nerve is inhibited and the valve subsequently opens and bacteria can then start to leak fecal content from the large intestine into the small intestine.

By the way, an example of where chronic stress can affect us negatively is in our workplace and according to the European Work Environment Agency one in five workers in Europe experiences work-related stress through high work demands, poor working environment and conflicts in the workplace.

Causes of SIBO

Reduced amount of hydrochloric acid in the stomach, usually via medication for "stress stomach" (gastritis/stomach inflammation) with gastric acid inhibitors (3, 5).

Impaired intestinal peristalsis can cause stagnation of food and thereby overgrowth of bacteria in the small intestine (2-5). An important cause of impaired intestinal motility is chronic stress.

Reduced closing capacity of the valve between the colon and the small intestine due to chronic stress.

Food poisoning via bacterial toxins from bacteria such as Campylobacter, Salmonella and Shigella, but also moderate alcohol consumption has been shown to contribute to SIBO (7).

How common is SIBO?

The incidence of SIBO varies depending on the population studied and the diagnostic criteria used. Surprisingly, scientific studies showed that up to 40% of healthy individuals tested positive for SIBO (8). No studies have so far investigated whether these healthy people who tested positive for SIBO developed health problems later on in life.

It's also worth mentioning that SIBO is more common in people with IBS (irritable bowel syndrome); up to 80% of people with IBS had SIBO (9). Also people on medications to treat stomach-acid issues had a higher incidence of SIBO (5). 

Symptoms of SIBO 

The symptoms of SIBO can be multifaceted and vary from person to person. Common symptoms include bloating, gas, abdominal pain, diarrhea or constipation, but also problems related to a leaky gut such as hypersensitivity to foods previously tolerated (cow's milk, eggs, grains, etc.) and low grade inflammation. These symptoms can often be confused with other gastrointestinal problems, making the diagnosis of SIBO challenging. 

It is highly important to rule out more serious causes of these symptoms such as cancer, inflammatory bowel diseases, etc.

Local symptoms (research has shown that over 80% of persons with IBS had SIBO):

  • Stomach pain or cramping
  • Bloated stomach
  • Gas and belching
  • Diarrhea
  • Constipation
  • Nausea
  • Heartburn / acid reflux

The rest of the body can also be affected in SIBO in the form of general symptoms of systemic low-grade inflammation, insulin resistance and cardiopulmonary problems (10-12).

General symptoms:

  • Fatigue
  • Joint pain
  • Muscle pain (e.g. as in fibromyalgia)
  • Food intolerance (e.g. gluten)
  • Skin inflammation / skin complaints (e.g. rosacea)
  • Depression/low mood

 

The gut-brain axis. The small intestine communicates with the brain via nerve fibers (vagus nerve) and via the bloodstream.

Gut bacteria and Parkinson’s disease

Parkinson's disease is thought to be caused by the protein α-synuclein clumping together
and forming toxic structures in the nerve cells. Research has previously shown that
α-synuclein occurs throughout the small intestine in people with Parkinson's disease. Previously, the cause of this accumulation of toxic α-synuclein structures has not been identified, but transport of α-synuclein via the so-called gut-brain axis has been proposed as one cause of Parkinson's disease.

Finnish researchers have recently identified an intestinal bacterium, Desulfovibrio, 
producing hydrogen sulphide, LPS and magnetite, which in close contact with the wall of the small intestine may cause this unfavorable aggregation of α-synuclein (13). From the small intestine α-synuclein could then be transported via the nerve pathways connecting the intestine to the brainstem, a region where Parkinson's disease is known to affect the dopamine neurons.

Gut bacteria and Alzheimer’s disease

Amyloid is a protein that accumulates in the brain in Alzheimer's disease. It has been shown that the bacterial toxin LPS from the intestinal bacterium Bacteroides fragilis can contribute to the deposition of amyloid in the brain and where it can clump together with amyloid in the brain in Alzheimer's disease (14, 15). In addition to the fact that LPS may increase the amount of amyloid in the brain, LPS has also been shown to cause a weakening of the cytoskeleton in nerve cells, which is typically seen in Alzheimer's disease (16, 17).

Treatment of SIBO

The treatment of SIBO usually includes a combination of antimicrobials, dietary changes and measures to improve intestinal peristalsis and management of stress. By reducing the amount of bacteria in the small intestine with antimicrobials, the symptoms can be alleviated, which in turn can contribute to reduced stress.

The most common pharmacological treatment for SIBO is using an intestinal antibiotic called rifaximin (Xifaxan®). Several studies indicate a connection between SIBO and diseases that affect the heart and vessels, endocrine organs, nervous system, kidneys, connective tissue and skin. Studies have shown that rifaximin not only reduced gastrointestinal symptoms but
also skin inflammation (rosacea) and other health problems linked to SIBO, with improved quality of life as a result (18-22).

A study showed that also botanical supplements with antibacterial properties can have equivalent effects as rifaximin (23).

Some advice 

  • Try botanical supplements with known antibacterial properties. Among others, oregano oil, magnolia bark, garlic, jatoba bark, rose root, ginger, and wormwood are considered to have these properties. SIBO supplements may also be composed of a mixture of antimicrobial botanicals.
  • Allow the small intestine to empty its contents by avoiding eating between meals. This allows the small intestine to rest and heal.
  • Mindfulness; try to do things in a calm and orderly manner.
  • Practice yoga and meditation.
  • Take deep breaths from time to time during the day. All of this can activate the beneficial vagus nerve.
  • Introduce regular and moderate exercise (e.g. walking).
  • Avoid an excessive intake of dietary fiber.
  • Intermittent fasting, with approximately 16 hours between main meals, is considered to contribute to increased intestinal motility. There also exist longer fasting programs.

In conclusion - what can we take away from this?

Unwelcome bacteria in the small intestine can cause local and systemic inflammatory conditions as well as affect the nervous system negatively.

Follow-up studies on whether healthy individuals with a positive SIBO test develop health problems have not yet been done, but regarding the nature of the small intestine, it may be considered beneficial to periodically try to reduce the occurrence of bacteria there. 

Stress reduction can both increase intestinal peristalsis and thus prevent stagnation of intestinal contents and reduce the reflux of bacteria from the large intestine to the small intestine.

In other words; the workhorses of the large intestine become “gut trolls” when they end up in the small intestine.

Gutfeeling Labs

info@gutfeelinglabs.se  

Gutfeeling Labs was founded by researchers in microbiology and neuroscience from Lund University, Sweden, to give the public the opportunity to increase their knowledge related to their intestinal flora and help to balance it.

Scientific references