It may not be the number of bacteria growing in our small intestine, but the type of bacteria, which can be corrected with diet.<\/p>\n
When researchers tested<\/a> more than a thousand patients suffering for longer than six months from symptoms typical with irritable bowel syndrome (IBS), such as excess gas, bloating, diarrhea, and abdominal pain, but who do not appear to have anything more serious going on, like inflammatory bowel disease, a significant percentage were found to be suffering from lactose intolerance\u2014intolerance to the milk sugar lactose. In infancy, we have an enzyme called lactase in our small intestine that digests milk sugar, but, understandably, most of us lose it after weaning. \u201cAlthough genetic mutation has led to persistence of lactase in adults, about 75% of the world\u2019s population malabsorbs lactose after age 30\u201d and have lactose intolerance. However, a third of the patients were diagnosed with small intestinal bacterial overgrowth (SIBO).<\/p>\n \u201cThe evidence for SIBO and IBS is shrouded<\/a> in controversy, predominantly because of the fact that the [breath] tests used in clinical practice to diagnose SIBO are not valid,\u201d as I\u2019ve explored before. As well, the implications of having more versus fewer bacteria growing in the small intestine are unclear since the number doesn\u2019t seem to correlate with the symptoms. It turns out it isn\u2019t the number of bugs growing<\/a> in the small intestine, but the type of bugs. So, it\u2019s \u201csmall intestinal microbial dysbiosis\u201d\u2014not overgrowth in general, but the wrong kind of growth\u2014that appears to underlie symptoms associated with functional gastrointestinal disorders, like IBS.<\/p>\n How can we prevent this from happening? The symptoms appear to be correlated with a significant drop in the number of Prevotella<\/em>. Remember them? Prevotella<\/em> are healthy fiber feeders, \u201csuggestive of a higher \ufb01ber intake in healthy individuals,\u201d while the bugs found more in symptomatic patients ate sugar, which \u201cmay re\ufb02ect a higher dietary intake of simple sugars.\u201d However, correlation doesn\u2019t mean causation. To prove cause and effect, we have to put it to the test, which is exactly what researchers did.<\/p>\n \u201cSwitching<\/a> a group of healthy individuals who habitually ate a high\u00ad-fibre diet (>11g per 1,000 calories) to a low\u00ad-fibre diet (was the type of bacteria growing, as you can see below, and at 3:12 in my video Fiber vs. Low FODMAP for SIBO Symptoms<\/a><\/strong>.<\/p>\n No wonder their guts got<\/a> leaky. Levels of short-chain fatty acids plummeted. Those are the magical by-products our good gut bugs make from fiber, which \u201cplay an important role in epithelial [intestinal] barrier integrity,\u201d meaning they keep our gut from getting leaky.<\/p>\n So, while we don\u2019t have<\/a> sound data to suggest that something like a low FODMAP diet has any benefit for patients with SIBO symptoms, there have<\/a> been more than a dozen randomized controlled trials that have put fiber to the test. Overall, researchers found<\/a> there was a signi\ufb01cant improvement in symptoms among those randomized to increase their \ufb01ber intake. That may help explain<\/a> why \u201chigh-fiber, plant-based diets can prevent many diseases common in industrialized societies.\u201d Such diets have this effect \u201con the composition and metabolic activity of the colonic microbiota.\u201d Our good gut bugs take plant residues like fiber and produce \u201chealth-promoting and cancer-suppressing metabolites\u201d like short-chain fatty acids, which have profound anti-inflammatory properties. \u201cAll the evidence points to a physiological need for ~50 g fiber per day, which is the amount contained in the traditional African diet and associated with the prevention of westernized diseases.\u201d That is approximately twice the typical recommendation and three times more than what most people get on a daily basis. Perhaps it should be no surprise that we need so much. Even though we split<\/a> from chimpanzees millions of years ago, \u201cthere is still broad congruency\u201d in the composition of our respective microbiomes to this day. While they\u2019re still eating their 98 to 99 percent plant-based diets to feed their friendly flora with fiber, we\u2019ve largely removed fiber-rich foods from our food supply.\u00a0<\/p>\n![\"\"](\"https:\/\/nutritionfacts.org\/app\/uploads\/2025\/09\/3-12.png\")
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