SIBO Symptom: Diarrhea and What You Can Do About It

Content
1. The Bristol Stool Chart
1.1 Stool Classifications
1.2 Stool Interpretation
2. . The Physiological Cause of Diarrhea
2.1 Diarrhea Due to Infection
2.2 Inflammatory Bowel Disease
2.3 Anxiety as a Cause
3. Diarrhea in SIBO
3.1 What is SIBO
3.2 SIBO as a cause of Diarrhea
3.3 Hydrogen Sulfide as a Cause of SIBO
4. Diarrhea Due to Irritable Bowel Syndrome (IBS)
4.1 Low FODMAP Diet for Diarrhea Caused by IBS
5. What to Do About Diarrhea
5.1 Water and Salt
5.2 Easy-to-Digest Foods and Pectin
5.3 Low-FODMAP Diet

Diarrhea can have many digestive causes and doesn’t only occur after infections. It is also a common symptom in chronic conditions such as SIBO (Small Intestinal Bacterial Overgrowth) and Crohn’s disease, and is frequently reported by people who have SIBO. In both cases, disruption in the small intestine and intestinal environment—especially involving bacterial overgrowth—can impair nutrient absorption and fluid regulation.
This article explores the causes of diarrhea, its connection to SIBO symptoms, and how specific treatment options and dietary strategies can help manage it.

1. The Bristol Stool Chart

The Bristol Stool Form Scale is a standardized chart used to classify the appearance and consistency of human stools. This classification can help clinicians assess intestinal health and monitor conditions like SIBO, Crohn’s, and bacterial imbalances in the small bowel or stomach.

1.1 Stool Classifications

Type 1 consists of separate, hard pellets that are difficult to pass; Type 2 describes a sausage-like, lumpy form; Type 3 is sausage-shaped with a cracked surface; Type 4 is sausage-shaped with a smooth surface; Type 5 consists of soft, smooth-edged lumps; Type 6 consists of soft, irregular-edged lumps (considered diarrhea), and Type 7 is liquid with no solid parts (severe diarrhea).

1.2 Stool Interpretation

Types 3-5 are considered normal, while Types 1 and 2 indicate constipation (common in low motility due to SIBO or antibiotics), and Types 6 and 7 indicate diarrhea (1) (e.g. because of active bacterial overgrowth, improper absorption, which may be associated with small bowel dysregulation, food intolerance, or e.g. post-lactulose test reactions).

2. . The Physiological Cause of Diarrhea

Diarrhea typically occurs when the intestines are unable to absorb water properly from digested food. In bacterial conditions like SIBO, excess bacteria in the small intestine may ferment carbohydrates, produce toxins, or trigger inflammation—leading to excess fluid in the bowel.
Additionally, antibiotics or poor enzyme function in the stomach or small bowel can interfere with nutrient absorption, while long-term bacterial overgrowth may impact vitamin B12 uptake, worsening overall health outcomes.

2.1 Diarrhea Due to Infection

When the body detects an invasion by bacteria, viruses, or parasites, it often triggers diarrhea as a rapid defense mechanism. This type of response helps flush harmful agents from the intestinal tract, protecting the digestive system. Infections may also lead to temporary bacterial overgrowth in the small intestine, which can resemble early SIBO symptoms.

2.2 Inflammatory Bowel Disease

Chronic conditions like Crohn’s disease are known to damage the intestinal lining, resulting in inflammation and poor nutrient absorption. As the small bowel becomes inflamed, people may experience recurring diarrhea due to impaired intestinal function. In many cases, long-term inflammation in Crohn patients may coexist with SIBO, making diagnosis and treatment more complex.

2.3 Anxiety as a Cause

Stress and anxiety can significantly affect digestive health. The gut-brain axis plays a major role in regulating bowel movements, and heightened stress can trigger diarrhea through the autonomic nervous system. This functional disturbance may worsen existing SIBO symptoms or lead to bacterial overgrowth when gut motility is impaired over time.

3. Diarrhea in SIBO

3.1 What is SIBO

SIBO (Small Intestinal Bacterial Overgrowth) occurs when bacteria multiply excessively in the small intestine, an area that typically contains very few microbes. In a healthy state, the small bowel is protected by stomach acid, enzymes, and motility. However, factors like low stomach acid, slowed transit, or frequent antibiotics use can disrupt this balance, encouraging overgrowth.
When people have SIBO, excess bacteria ferment nutrients and release gas and toxins, which damage the gut lining. This causes a range of SIBO symptoms, including abdominal pain, bloating, diarrhea, constipation, belching, fullness, and even vitamin B12 deficiency due to absorption issues.There are three primary types of SIBO based on the gas bacteria produce: _{Hydrogen-dominant (H₂)}, _{Methane-dominant (CH₄)}, _{Hydrogen sulfide-dominant (H₂S)}
The condition is typically diagnosed using a lactulose or glucose breath test and requires targeted treatment based on gas type and patient history.

3.2 SIBO as a cause of Diarrhea

SIBO (Small Intestinal Bacterial Overgrowth) can lead to chronic diarrhea by disrupting the small intestine’s ability to absorb nutrients (4). As undigested food particles accumulate, they attract water into the bowel, resulting in loose stools. This is a hallmark among many SIBO symptoms.
In addition, bacteria involved in SIBO ferment food and release gases and byproducts that damage the intestinal lining. People with SIBO often also experience motility disorders, further exacerbating these digestive issues. Inflammation (5) caused by bacterial overgrowth may compromise water absorption and lead to malnutrition, including vitamin B12 deficiency.

3.3 Hydrogen Sulfide as a Cause of SIBO

A specific subtype of SIBO involves hydrogen sulfide-producing bacteria, which are especially common in hydrogen and hydrogen sulfide-dominant SIBO. These gases irritate the intestinal lining and are strongly associated with diarrhea and gut inflammation.
This subtype of bacterial overgrowth has also been linked to diarrhea-predominant IBS-D (6). The toxic effects of hydrogen sulfide may impair the small bowel’s mucosal barrier, leading to increased permeability and water imbalance in the gut (7,8).

4. Diarrhea Due to Irritable Bowel Syndrome (IBS)

In addition to SIBO, IBS can also cause diarrhea. There are different subtypes of IBS: IBS-C (primarily constipation), IBS-D (primarily diarrhea), and IBS-M (a mix of constipation and diarrhea). Those who cannot be clearly classified into one of these subtypes are categorized as IBS-U (2). Patients with IBS-D often experience bloating, urgency, and altered bowel frequency, similar to SIBO symptoms. Distinguishing between bacterial or functional causes is key for targeted treatment.

4.1 Low FODMAP Diet for Diarrhea Caused by IBS

A Low FODMAP diet can help alleviate symptoms of diarrhea, especially in IBS-D, and is a recommended approach for managing IBS (3). This diet eliminates fermentable carbohydrates from the diet. FODMAPs are found in foods like onions, garlic, and legumes, which are not fully digested by the human intestine, and thus serve as food for gut bacteria. The gases and byproducts produced in the process can cause symptoms. However, the list of FODMAP foods is not limited to these; fructose (fruit sugar) and lactose (milk sugar) are also FODMAPs. Therefore, milk products and certain fruits and vegetables can cause symptoms like bloating and diarrhea in IBS. A Low FODMAP treatment plan should ideally be developed with the support of a digestive health specialist or dietitian, especially for those recovering from SIBO, Crohn, or long-term use of antibiotics.

5. What to Do About Diarrhea

5.1 Water and Salt

An essential part of treatment for diarrhea—whether due to SIBO, Crohn, or acute infection—is replenishing lost fluids and electrolytes. When people experience watery stools, they lose vital minerals that help regulate digestive health.
Drinking mineral-enriched water and teas like chamomile or fennel can soothe the intestinal lining and help restore balance in the small bowel. These supportive measures are particularly helpful in cases involving bacterial overgrowth, where chronic diarrhea can dehydrate the body and disrupt normal intestinal function.
(9,10).

5.2 Easy-to-Digest Foods and Pectin

Simple, digestive-friendly foods such as dry toast, bananas, and grated apples are classic home remedies. These foods are gentle on the small intestine and provide people with relief while the gut recovers.
Apples and bananas are also rich in pectin, a soluble fiber that absorbs excess fluid in the intestinal tract and helps form firmer stools. Grated apple with the skin on provides even more pectin, supporting those who have SIBO or Crohn and need to calm gut activity during flare-ups.

5.3 Low FODMAP Diet

For people with SIBO or IBS, following a Low FODMAP diet can reduce diarrhea and bloating. This treatment approach involves temporarily removing bacteria-fermenting carbohydrates—often the fuel behind bacterial overgrowth in the small intestine.Trigger foods include: garlic, onions, cabbage, legumes like lentils.
Reducing FODMAPs limits gas production by bacteria in the gut, which in turn helps control digestive distress.

If diarrhea continues or is accompanied by symptoms such as fever, it’s important to seek medical advice for further treatment and testing.

References

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