The human digestive system is complex, and symptoms like bloating, gas, and abdominal pain are common. These issues often arise from problems in how the body processes food or manages its microbial residents. A frequent question involves the connection between Small Intestinal Bacterial Overgrowth (SIBO) and lactose intolerance. While distinct conditions, one can directly contribute to the development of the other.
What SIBO Is and How It Develops
Small Intestinal Bacterial Overgrowth (SIBO) is defined by an abnormally high number of bacteria in the small intestine, often types that typically reside in the large intestine. The small bowel naturally contains a low concentration of microbes. When this balance is disrupted, symptoms can include diarrhea, excessive gas, abdominal distension, and uncomfortable fullness.
SIBO typically develops when the small intestine’s natural cleansing mechanisms fail to control the bacterial population. A primary cause is impaired motility, where sluggish muscular contractions allow bacteria to linger and multiply.
Other contributing factors include structural abnormalities, such as diverticula or surgical blind loops, and conditions that decrease stomach acid production. The resulting bacterial colonization leads to various digestive complications, including the malabsorption of fats, carbohydrates, and proteins.
Understanding Lactose Intolerance
Lactose intolerance (LI) is the inability to fully digest lactose, the sugar found in dairy products, due to a deficiency of the enzyme lactase. Lactase breaks down lactose into two simpler, absorbable sugars.
When lactase levels are insufficient, undigested lactose travels into the large intestine. Resident bacteria ferment the sugar there, producing gases and short-chain fatty acids, which cause bloating, pain, and diarrhea.
LI is categorized by cause. Primary LI involves a natural decline in lactase production after childhood. Secondary LI is caused by damage to the small intestinal lining due to injury, infection, or disease.
The Direct Connection: SIBO’s Impact on Lactase Activity
The connection between SIBO and lactose intolerance is rooted in secondary lactase deficiency. Lactase is anchored to the brush border—the microscopic villi that line the small intestine wall. These villi are crucial for carbohydrate digestion and nutrient absorption.
In SIBO, the excessive bacterial presence causes chronic inflammation and physical damage to these delicate brush border cells. The invading bacteria and their metabolic byproducts injure the cells responsible for producing the lactase enzyme. This destruction directly impairs the body’s capacity to utilize lactase, resulting in a temporary deficiency.
SIBO can thus directly cause secondary lactose intolerance, leading to LI symptoms even in individuals who previously tolerated dairy. The severity of SIBO often correlates with the degree of intestinal damage and the severity of LI symptoms experienced.
Testing and Management of the Co-occurring Conditions
Because SIBO and lactose intolerance share overlapping symptoms, a sequential diagnostic approach is necessary. The primary non-invasive test for SIBO is the hydrogen and methane breath test, measuring gas levels after the patient ingests a sugar solution. A separate hydrogen breath test, using a lactose solution, diagnoses lactose intolerance.
When both conditions are suspected, SIBO testing is prioritized because the lactose intolerance is frequently secondary to the bacterial overgrowth. Management focuses on treating the root cause, typically involving targeted antibiotics or specific herbal antimicrobial protocols to reduce the bacterial population.
Successful SIBO eradication allows the damaged small intestinal lining to heal. As the brush border recovers, cells can resume normal lactase production, often leading to the resolution of the lactose intolerance over time. Managing LI symptoms during treatment may involve temporary dietary restrictions or supplemental lactase enzymes.