Can a Gluten-free Diet Damage Gut Bacteria?
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The Spanish study follows just ten individuals for just one month on gluten-free diets. A large-scale, long-term study might make very different observations, and reach very different conclusions.
The study found no significant differences in dietary intake before and after the gluten-free diet except for reductions (P=0.001) in polysaccharides. Bifidobacterium, Clostridium lituseburense and Faecalibacterium prausnitzii proportions decreased (P=0.007, P=0.031 and P=0.009, respectively) as a result of the GFD analysed by fluorescence in situ hybridisation (FISH). Bifidobacterium, Lactobacillus and Bifidobacterium longum counts decreased (P=0.020, P=0.001 and P=0.017, respectively), while Enterobacteriaceae and Escherichia coli counts increased (P=0.005 and P=0.003) after the GFD assessed by quantitative PCR (qPCR). TNF-alpha, interferon-gamma, IL-10 and IL-8 production by PBMC stimulated with faecal samples was also reduced (P=0.021, P=0.037, P=0.002 and P=0.007, respectively) after the diet.
The study doesn't provide any real evidence to support a conclusion one way or the other, especially their conclusion that a gluten-free diet "may constitute an environmental variable to be considered in treated Coeliac disease patients for its possible effects on gut health."
The fact is that beneficial, probiotic bacteria in the human gut are influenced by diet. The more fruits, vegetables, and high fiber foods we consume, the healthier our bacteria will be.
The Spanish study makes no mention of the subjects' diets. Were they fed high fiber, low fat diets rich in fruits and vegetables, or did they eat a standard western diet with no gluten?
It would be interesting to compare the gut bacteria levels of people before celiac disease diagnosis and after celiac disease diagnosis to see if a gluten-free diet improves gut bacteria overall, or if the Spanish results would be seen again.
Br J Nutr. 2009 May 18:1-7.
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