The term “leaky gut” (altered intestinal permeability syndrome) is a condition in which the intestine becomes porous and less able to act as a barrier to food, bacteria, fungi,and/or allergens. It is well established that dietary components (such as fibers) are associated with maintaining or restoring normal gut barrier.
To assess intestinal and colonic permeability, oral monosaccharides and disaccharides are used as probes to measure in vivo human gut permeability through urinary excretion. However, there is no conformity in the literature regarding the methods used to characterize intestinal barrier function. Moreover, alcohol intake, differences in diet, age, sex, BMI, and different types could influence gut permeability.
In order to standardize and identify normal values of small intestinal and colonic permeability in healthy human adults, Khosbin and colleagues measured small intestinal and colonic permeability based on urine excretion of oral probe molecules in 60 healthy, white, female and male adults, aged 18-70 years. Since the fiber content of the diet could positively influence intestinal permeability, the author divided participants in 3 randomized studies with different fiber doses intake (2 studies on 16.25g and 1 on 32.5g fiber). For the test 12C-mannitol, 13C-mannitol, rhamnose (monosaccharides), sucralose and lactulose (disaccharides) sugars were ingested after administration of fiber-containing meals, and urine was collected three times: 0-2, 2-8, and 8-24h after sugars ingestion. In addition, 13C-mannitol and lactulose were administrated to 18 patients with diarrhea-predominant irritable bowel syndrome (IBS-D), in order to assess the applicability of the method in patients.
Results showed median excretions/24h of ~30%, for 13C-mannitol, ~15%, rhamnose, 0.32% lactulose and 2.3% sucralose. 13C-mannitol proved to be the most optimal in reflecting small intestinal permeabiliy. Moreover, 13C-mannitol is also measureable in IBS-D individuals. Finally, there were no significant effects of sex, age, or BMI on permeability measurements.
Data suggest that 13C-mannitol could be used to developed a clinical diagnostic test to evaluate small intestinal permeability in vivo in humans. Nevertheless, Koshbin and colleagues admit the lack of data regarding obesity, characterized by a predominantly increased permeability in association with complications such as diabetes, hepatic steatosis and systemic inflammation, and suggest further studies to substantiate their results.
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