The small intestine is the part of the gastrointestinal (GI) tract that connects the stomach to the colon. Its primary function is the facilitation of the digestion process and the absorption of nutrients into the bloodstream.  The colon contains bacteria which further facilitates digestion before eliminating waste from the body. In a healthy individual, bacteria are naturally housed throughout the entire digestive tract.  The small intestine, compared to the colon, houses relatively low levels of these microorganisms, with the colon having the highest concentration. A further difference is that the small intestine will contain specific strains of bacteria which differ from those found within the colon.

Small Intestinal Bacterial Overgrowth (SIBO) refers to a condition in which abnormally large quantities of bacteria, which are usually more specific to the colon, are present within the small intestine. This has been shown to negatively affect both the structure and function of the small intestine, considerably interfering with digestion and the absorption of nutrients, primarily by damaging the small intestinal mucosa. The endotoxins produced by the bacteria also damage the tight junctions found in the small intestine which are designed to create a protective barrier between substances entering from the ‘outside world’ and internally. This damage can lead to leaky gut due to increased intestinal permeability, thus allowing large protein molecules to escape into the bloodstream. This has been associated with increased IgG antibody immune reactions, resulting in generalised inflammation and an increased potential to develop food hypersensitivities/intolerance.

When bacteria proliferate and overrun the small intestine, they can also impair the body’s ability to absorb essential nutrients, thus possibly leading to severe nutrient deficiencies. Fat absorption may be inhibited for example, through their effect upon bile acids, which can in turn lead to deficiencies in fat soluble vitamins. In addition to this, bacteria may in fact consume some of the nutrients that are ingested by an individual, including Vitamin B12 and iron, thus increasing the risk of anaemia. They may also consume some of the amino acids that we ingest from the protein in our diet, potentially resulting in mild protein deficiency and ammonia production, which in turn places extra burden upon the detoxification system. A potentially embarrassing effect is that after consuming an individual’s food, the bacteria produce gas within the gut, which can cause flatulence, abdominal pain and bloating, diarrhoea and/or constipation.

Several risk factors for SIBO have been identified, including:

  • Multiple courses of antibiotics
  • Low stomach acid
  • Moderate to heavy alcohol consumption
  • Oral contraceptive pills
  • IBS
  • Celiac disease
  • Crohn’s disease
  • Diabetes mellitus
  • Prior bowel surgery
  • Organ system dysfunction, such as liver cirrhosis, chronic pancreatitis, or renal failure

Treating SIBO requires a gut healing program which, if food intolerances are present, can be supported by the removal of the offending foods to help reduce some of the associated inflammation.