In an article published on my blog a few months ago, I argued that quantitative culture, the “gold standard” for diagnosing small intestinal bacterial overgrowth (SIBO), is outdated, that breath testing does not accurately diagnose SIBO, and that small intestinal dysbiosis is likely the culprit in many patients with IBS-like symptoms.
Now, a study published in Nature Communications has confirmed that small intestinal dysbiosis, rather than bacterial overgrowth, underlies most GI symptoms. The researchers evaluated 126 symptomatic patients and 38 healthy volunteers who underwent testing for SIBO via upper endoscopy and aspiration of the duodenum. Of the 126 patients, 66 were positive for SIBO by culture criteria, but there was NO correlation between SIBO and symptoms.
When they looked at microbial composition, however, symptomatic patients had lower bacterial diversity, lower species richness, and a reduced abundance of Prevotella, Porphyromonas, and Fusobacterium in the duodenal aspirates compared to healthy volunteers, and 29 percent of the participants had significant gut dysbiosis. Symptomatic patients also had a predicted enrichment of bacterial pathways associated with simple sugar metabolism, whereas healthy individuals had pathways involved in complex carbohydrate degradation.
This led the researchers to want to examine the impact of diet on GI symptoms. They put 16 healthy subjects who habitually consumed a high-fiber diet on a low-fiber, high simple-sugar diet for one week. Eighty percent of the subjects developed GI symptoms during the intervention, which resolved within a week of returning to their high-fiber diet. There was a strong negative correlation between small intestinal microbial diversity and small intestinal permeability. Perhaps most interestingly, they found that half of the healthy individuals consuming a high-fiber diet had SIBO by culture criteria!
Overall, this study confirms that we should NOT be using culture to diagnose SIBO, and that we need to start focusing more on microbial composition, not total bacterial abundance in treating GI symptoms. Moreover, it highlights the importance of fiber in protecting against GI disorders.
Read the full study here: https://www.nature.com/articles/s41467-019-09964-7