SIBO: What Lies Behind the Condition Mistaken for a Disease, Part 1

SIBO (Small Intestinal Bacterial Overgrowth) is a condition where bacteria that are normally present in small amounts in the small intestine—or that typically reside in the large intestine—begin to proliferate in the small intestine. SIBO disrupts normal digestion and nutrient absorption.

Symptoms of SIBO include bloating, abdominal pain, diarrhea, or constipation. However, it’s not just discomfort—SIBO can significantly impact quality of life, leading to chronic fatigue, skin issues, weight loss, and vitamin and mineral deficiencies. The underlying cause of SIBO is often another condition, and SIBO is a dysfunction of the gut that results from this primary issue.

Functions of the Small and Large Intestines

As mentioned earlier, the problem with SIBO lies in the imbalance of the microbiota and digestive function. To understand why this condition causes problems, it’s important to examine the differences between the small and large intestines and their functions:

Small Intestine

• The main site for digestion and absorption of nutrients (proteins, fats, carbohydrates, vitamins, and minerals).
• Normally contains relatively few bacteria—10³ to 10⁶ bacteria per milliliter of contents. This low bacterial count is maintained by active peristalsis, bile flow, and enzymes under normal conditions.
  • Peristalsis: Regular contractions push contents toward the large intestine, preventing stagnation.
  • Stomach acid: Destroys pathogens ingested with food.
  • Bile acids and pancreatic enzymes: Inhibit bacterial growth by creating an unfavorable environment.
  • Ileocecal valve: Prevents backflow of material from the large intestine into the small intestine.

Large Intestine

• The primary site for fermentation of food remnants by bacteria.
• Contains a huge number of microbes—approximately 10¹¹ to 10¹² bacteria per gram of content, which is millions of times more than in the small intestine.
• The microbiota of the large intestine plays a key role in the production of short-chain fatty acids (SCFAs), immune system regulation, and the synthesis of vitamins (e.g., K2 and B vitamins).

Natural Defense Mechanisms Against SIBO

• Structural Defense:
  • Pyloric and ileocecal valves: These valves help prevent bacteria from entering the small intestine from the stomach and large intestine. The pyloric valve regulates the movement of food from the stomach to the small intestine, while the ileocecal valve limits bacterial migration from the colon into the small intestine.
• Chemical Defense:
  • Hydrochloric acid: The low pH in the stomach plays a key role in destroying most pathogenic bacteria ingested with food. Low stomach acid can promote bacterial overgrowth and contribute to SIBO.
  • Bile and enzymes: Bile helps break down fats and bacteria, while digestive enzymes break down proteins and carbohydrates. Impaired bile or enzyme production can hinder normal digestion and contribute to SIBO.
• Motility Defense:
  • Migrating Motor Complex (MMC): This cyclic process occurs between meals and helps clear the small intestine of food debris, bacteria, and other substances. Reduced MMC activity can lead to intestinal stagnation and bacterial overgrowth.

These defense mechanisms work in synergy to prevent SIBO and maintain a healthy gut microbiota. Disruption in any of them can increase the risk of developing SIBO.

Migrating Motor Complex (MMC)

Let’s take a closer look at what this is. The MMC includes several phases:

• Phase 1 (Resting phase): Minimal activity; the intestine is at rest (45–60 minutes).
• Phase 2 (Submaximal activity): Increased peristalsis, but not strong enough to move large contents (about 30 minutes).
• Phase 3 (Maximal activity): Strong wave of contractions that pushes food debris and bacteria out of the small intestine (5–10 minutes, repeating every 90–120 minutes).
• Phase 4 (Transitional phase): Transition from maximum activity back to rest.

The MMC is activated between meals and plays a key role in preventing excessive bacterial growth in the small intestine. Disruption of the MMC, for example in diabetes, hypothyroidism, or chronic stress, can lead to bacterial stagnation and SIBO.

Every 90 minutes, a wave of peristalsis occurs in the small intestine, helping to cleanse it of residual food and bacteria. However, this process can be negatively affected by stress and other factors. For instance, food poisoning can cause long-term damage to the motor complex.

How SIBO Affects the Body

When the natural protective mechanisms of the small intestine fail, bacteria from the large intestine begin to colonize the small intestine. Here are the problems this can cause:

• Gas Production in the Small Intestine:
  • Unlike the colon, the small intestine is not designed to handle large amounts of bacteria or gas. Trapped gas stretches the intestinal walls, causing pain, bloating, and a feeling of fullness.
  • Gases like hydrogen and methane can cause additional symptoms, including constipation or diarrhea.
• Mucosal Damage:
  • “Leaky gut”: Inflammation triggered by bacteria increases intestinal permeability, allowing toxins, bacteria, and undigested particles to enter the bloodstream.
  • Leaky gut may contribute to systemic inflammation and the development of autoimmune conditions.
  • Damage to intestinal villi can reduce the activity of enzymes like lactase, causing secondary lactose intolerance.
• Nutrient Deficiencies:
  • Vitamin B12: Bacteria in the small intestine may consume B12, leading to deficiency that affects the nervous system and blood cell production.
  • Folate: Bacteria may deplete folate, which is critical for cellular function and nervous system health.
  • Fats (especially fat-soluble vitamins): Issues with bile flow or intestinal function may impair fat digestion and absorption, affecting vitamins A, D, E, and K.
  • Minerals: Absorption of calcium, magnesium, and iron can be impaired, as healthy microbiota supports this process, which is disrupted in SIBO.
  • Proteins: Protein and amino acid absorption may suffer, as the microbiota plays a key role in digestion.
• Systemic Effects:
  • Toxic bacterial metabolites (endotoxins) may enter the bloodstream, causing fatigue, headaches, skin issues, and more.
  • Microbiota imbalance may worsen IBS symptoms and impact mental health through the gut-brain axis.
• Immune Dysregulation:
  • Chronic intestinal inflammation burdens the immune system, increasing risks for allergies, food intolerances, and autoimmune disorders.

SIBO Symptoms

Let’s summarize the possible symptoms of SIBO:

Symptom Category	Symptoms
Primary GI Symptoms	Abdominal bloating (gas): belching, flatulence
	Abdominal pain and cramping
	Constipation, diarrhea, or alternating between both
Additional GI Symptoms	Heartburn (reflux or GERD)
	Nausea
Leaky Gut Symptoms	Food sensitivities to multiple foods
	Headaches
	Joint pain
	Fatigue, brain fog
	Skin manifestations (eczema, rashes)
	Respiratory symptoms (asthma)
	Emotional symptoms (depression, anxiety, concentration issues)
	Neurological symptoms (e.g., autism)
Malabsorption Symptoms	Steatorrhea (fatty stools), fat-soluble vitamin deficiencies: A, D, E, K
	Anemia (iron or B12 deficiency)
	Weight loss or weight gain

Primary Causes of SIBO

Intestinal Motility Disorders

• Slowed peristalsis: delayed movement of food and waste, common in diabetes, hypothyroidism, or post-surgical states.
• Nervous system dysfunction: chronic stress, depression, or diseases affecting the autonomic nervous system.
• Valve dysfunction: impaired ileocecal valve or Peyer’s patches may allow backflow of bacteria from the colon into the small intestine.
• Chronic constipation: can promote bacterial backflow from the colon.
• Food poisoning: damages intestinal motor function, impairing clearance of excess bacteria.

Impaired Gastric Acid and Enzyme Activity

• Low stomach acid: due to proton pump inhibitors (PPIs), hypochlorhydria, or gastric atrophy, promoting bacterial overgrowth.
• Digestive enzyme deficiency: disrupts the microbiome and promotes growth of harmful bacteria.

Anatomical Abnormalities

• Post-surgical changes: structural alterations after stomach or intestinal surgeries.
• Bowel obstructions: caused by adhesions or scarring, leading to stagnation and bacterial overgrowth.

Immune System Disorders

• Immunodeficiency: Conditions such as autoimmune diseases, chronic infections, or long-term immunosuppressant use can compromise the gut’s immune response.
• Impaired Gut Barrier Function: Inflammatory diseases like Crohn’s disease or ulcerative colitis can allow bacteria to penetrate the small intestine.
• Autoimmune Diseases: Disorders like rheumatoid arthritis can also influence intestinal motility.

Microbiota Disruption

• Antibiotic use: disrupts the balance of gut flora, encouraging harmful bacteria.
• Excess carbohydrate and sugar intake: fuels overgrowth of undesirable bacteria, including those linked to SIBO.
• Dysbiosis: imbalance between beneficial and harmful bacteria.
• Post-infectious flora issues: prior intestinal infections or parasitic diseases can trigger SIBO development.

Hormonal Changes

• Hypothyroidism: reduced thyroid hormones slow down intestinal motility, promoting stagnation and bacterial growth.
• Diabetes: nerve damage and slow motility encourage bacterial overgrowth.
• Sex hormone shifts: hormonal changes during menopause can disrupt intestinal function.

External Factors

• Chronic stress: impacts gut motility and immune system, contributing to SIBO.
• High-sugar, processed food diet: promotes harmful bacteria and disturbs gut flora balance.
• Low fiber intake and poor digestion: insufficient fiber impairs motility and microbiota health.

Conditions Associated with SIBO

This list includes diseases that may contribute to or worsen SIBO. Some affect motility, immunity, or gut permeability, increasing the risk of small intestinal bacterial overgrowth. People with these conditions are at higher risk of developing SIBO, and its presence may aggravate the primary condition’s symptoms.

Rosacea	Acromegaly	Anemia
Atrophic gastritis	Autism	Crohn’s disease
Lyme disease	Parkinson’s disease	Age: elderly
Gastroparesis	Hypochlorhydria	Hypothyroidism / Hashimoto’s thyroiditis
GERD (gastroesophageal reflux)	Diverticulitis	Diabetes
Dyspepsia	Gallstones	Fatty liver disease
Interstitial cystitis	H. pylori infection	Medications: PPIs, opioids, NSAIDs
Minimal hepatic encephalopathy	Myeloma tumors	Cystic fibrosis
Muscular dystrophy (type 1)	Lactose intolerance	NAFLD/NASH (nonalcoholic fatty liver disease / steatohepatitis)
Surgeries: post-gastrectomy	Pancreatitis	Parasites
Chronic prostatitis	Rheumatoid arthritis	Restless leg syndrome
Leaky gut syndrome	Chronic fatigue syndrome	Scleroderma
IBS (Irritable Bowel Syndrome)	Fibromyalgia	Celiac disease
Liver cirrhosis	Chronic lymphocytic leukemia (CLL)	Erosive esophagitis

Conclusion

SIBO is a serious disruption of the microbial balance in the small intestine that can lead to numerous symptoms, including digestive issues, nutrient deficiencies, and systemic inflammation. Understanding the differences between the functions of the small and large intestines helps explain the mechanisms behind SIBO and related issues such as gas production, mucosal inflammation, and vitamin deficiencies. Impaired intestinal motility, along with dysfunctions in chemical and structural defenses, are key contributors to bacterial overgrowth.

Diagnosis and treatment of SIBO and related conditions will be discussed in detail in the second part, which will also explore how factors such as hormonal changes and stress influence the development of this condition.