Breath testing is commonly used to diagnose Small Intestinal Bacterial Overgrowth (SIBO), but it could also be used to identify Large Intestine Bacterial Overgrowth (LIBO). The SIBO breath test measures amounts of the gasses hydrogen and methane produced by bacteria in the small intestine when they ferment carbohydrates. However, these breath tests also assess the hydrogen and methane gas activity in the large intestines. In most cases, this data is ignored, but this oversight may prevent proper diagnosis and treatment.

SIBO vs LIBO

In a healthy digestive system, the small intestine has relatively few bacteria compared to the large intestine. However, in SIBO, an overgrowth of bacteria in the small intestine ferments carbohydrates prematurely. This fermentation produces gasses, primarily hydrogen, methane, or hydrogen sulfide, which are absorbed into the bloodstream and then exhaled through the lungs. After a patient ingests a specific carbohydrate substrate, like lactulose or glucose, the breath test detects the levels of these gasses. Abnormally high levels indicate bacterial overgrowth in the small intestine.

The large intestine, or colon, is naturally populated with a vast number of bacteria responsible for fermenting undigested carbohydrates. This fermentation produces gasses like hydrogen, methane, and carbon dioxide as a normal part of digestion. Because this process is a normal function of the large intestine, the conventional medical community believes that assessing gas activity of the colon has no diagnostic value. In other words, elevated gas levels detected later in the breath test are expected, to some degree, and therefore do not specifically indicate pathology.

Large Intestinal Bacterial Overgrowth (LIBO) is a condition where there is an abnormal increase in the number and/or types of bacteria in the large intestine (colon). While the colon normally contains a vast and diverse population of bacteria that play essential roles in digestion, immunity, and overall health, an imbalance or overgrowth of certain bacterial species can lead to digestive issues and other health problems.

Key Aspects of Large Intestinal Bacterial Overgrowth (LIBO)

Causes of LIBO

• Dietary Factors: A diet high in refined carbohydrates or sugars and low in fiber can promote bacterial overgrowth in the large intestine.
• Dysbiosis: An imbalance in the gut microbiota, often caused by factors like antibiotics, poor diet, chronic stress, or other medications, can lead to LIBO.
• Slow Transit Time: Conditions that slow down the movement of food through the colon, such as constipation, can lead to bacterial overgrowth as bacteria have more time to ferment undigested food.
• Immune System Dysfunction: A weakened immune system, which fails to keep bacterial populations in check, can contribute to LIBO.

Symptoms of LIBO

• Abdominal Bloating and Gas: Excess fermentation of undigested carbohydrates by bacteria can produce large amounts of gas, leading to bloating and discomfort.
• Diarrhea or Constipation: LIBO can cause changes in bowel habits, leading to either diarrhea (due to rapid fermentation and irritation) or constipation (due to slower transit and hard stools).
• Abdominal Pain: The buildup of gas and changes in motility can cause cramping and discomfort in the abdomen.
• Fatigue and Malaise: Chronic LIBO can lead to malabsorption of nutrients, resulting in fatigue, nutrient deficiencies, and general feelings of unwellness.

Hydrogen Gas Production in the Large Intestine

The large intestine is home to a vast and diverse community of bacteria, many of which play a key role in digesting food components that were not fully broken down in the small intestine. These bacteria ferment undigested carbohydrates, fibers, and other nutrients, producing gasses as byproducts. Hydrogen gas (H₂) is one of the primary gasses produced during this fermentation process.

When carbohydrates, especially complex carbohydrates and fibers, reach the large intestine, they become substrates for bacterial fermentation. The bacteria break down these carbohydrates to obtain energy, and in the process, hydrogen gas is released along with other gasses like carbon dioxide (CO₂) and methane (CH₄).

Fate of Hydrogen Gas in the Large Intestine

• Hydrogen-Consuming Microbes: In a healthy gut, hydrogen gas produced by one group of bacteria is often consumed by other microbes. For example:

• • • Methanogenic Archaea: These microbes convert hydrogen gas into methane, which is another gas commonly found in the colon.
    • Sulfate-Reducing Bacteria: These bacteria use hydrogen to reduce sulfate to hydrogen sulfide (H₂S).
    • Acetogens: These microbes can convert hydrogen gas into acetate, which is a short-chain fatty acid beneficial for gut health.
• Exhalation and Flatulence: Some of the hydrogen gas is absorbed into the bloodstream and then exhaled through the lungs, which is why hydrogen breath tests are used to diagnose certain gastrointestinal conditions. The remaining hydrogen gas, along with other gasses produced in the colon, can be expelled as flatulence.

Conditions Influencing Hydrogen Production in the Large Intestine

• Dietary Composition: Diets high in fermentable fibers, sugars, and complex carbohydrates can increase hydrogen gas production in the large intestine because they provide more material for bacterial fermentation.

• Gut Microbiome Balance: The balance of different types of bacteria in the large intestine influences hydrogen production. A healthy balance means that hydrogen production and consumption are balanced, minimizing excess gas.

• Digestive Disorders: Conditions like irritable bowel syndrome (IBS), small intestinal bacterial overgrowth (SIBO), or malabsorption syndromes can lead to increased hydrogen production, contributing to symptoms like bloating, discomfort, and gas.

Summary

Hydrogen gas is indeed produced in the large intestine as a result of bacterial fermentation of undigested carbohydrates and fibers. The gas is either consumed by other gut microbes, absorbed into the bloodstream and exhaled, or expelled as flatulence. The production of hydrogen gas in the colon is a normal part of digestion, but excessive production may contribute to digestive discomfort, bloating, excessive flatus, irritable bowel symptoms and may suggest the presence of LIBO. Total hydrogen activity assessed during breath tests, e.g. the Neurovanna Total SIBO Bacterial Load, offer another functional diagnostic tool for assessing the presence and extent of LIBO. 

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Learn more about the author, Dr. Bradley Bush.