The small intestinal bacterial overgrowth syndrome (SIBO) is dangerous because bacteria actively colonize the small intestine. Several unfavorable mechanisms occur:
Competition for nutrients. Bacteria begin to "intercept" vitamins and minerals before they can be absorbed in the walls of the small intestine.
Mucosal damage and inflammation. The overgrown bacteria release toxins and fermentation products. This irritates the mucosa, triggers chronic inflammation, and increases the permeability of the intestinal wall. As a result, even those nutrients that reach the absorption site pass through the damaged barrier less effectively.
Digestive disruption. Due to bacterial activity, bile acids and enzymes are less effective, disrupting the breakdown of fats, proteins, and carbohydrates. This not only reduces nutrient absorption but also increases gas production, bloating, diarrhea, or, conversely, constipation.
Metabolic consequences. Bacteria can synthesize their own substances, including D-lactic acid. Its accumulation in some people causes symptoms similar to neurological disorders—fatigue, "brain fog," and decreased concentration.
Thus, in SIBO, a vicious cycle forms: the more bacteria there are, the more nutrient deficiencies arise, and these deficiencies, in turn, weaken the function of the mucosa and the intestinal immune system, further facilitating the growth of microbes.
Which nutrients are affected by SIBO
Here are the main vitamins and minerals whose deficiency often develops.
Vitamin B12 (cobalamin). Bacteria actively capture B12 and use it for their own metabolism, leaving very little for the human host.
Iron. Bacteria alter pH and damage the mucosa, hindering iron absorption. Additionally, during intestinal inflammation, the body "hides" iron in tissues, reducing its availability.
Vitamin D. Disruption of fat emulsification in SIBO decreases its absorption.
Vitamin A (retinol). It is also affected by impaired fat absorption.
Vitamin K. It is normally partially produced by the microflora of the large intestine. In SIBO, the balance and synthesis are disrupted.
Calcium. Its absorption is directly related to vitamin D and the healthy state of the mucosa. In SIBO, transport through the intestinal wall is impaired.
Magnesium. Chronic diarrhea and intestinal inflammation lead to its loss.
Zinc. Bacteria also compete for it, plus inflammation worsens transport.
