Effects of Gluten on Gut Bacterial Composition Jessica Leary Russell Sage College

Abstract Gut microbiota consists of hundreds of thousands of microorganisms located in the human intestines that are greatly affected by changes in diet. 1 One of the microbiota’s main sources of food are polysaccharides commonly found in fruits, vegetables, nuts and seeds, but many times are taken in through whole grain consumption. Whole grains including whole wheat, barley and rye, are some of the main components of breads, pastas, and cereal, all of which contain the protein gluten. 6,10 For those on a gluten free diet, this can pose the problem of not ingesting enough complex carbohydrates needed for bacteria to feed. 1,12 Analysis of current research shows that differences in the substances consumed between gluten containing and gluten free diets negatively affects gut flora allowing pathogenic bacteria to colonize the gut. In particular, the beneficial bacteria Lactobacillus and Bifidobacterium declined significantly (P=0.001 and P=0.020 respectively) while pathogenic bacteria like the Enterobacteriaceae group and Escherichia coli increased significantly (P=0.005 and P=0.003 respectively). Hypotheses have been introduced as to what may be done to counteract these effects, specifically through change in diet and probiotic administration.

Human: Host to Bacteria The human body is host to thousands of strands of beneficial bacteria, many concentrated in the gut Figure 1. Polysaccharide-degrading bacteria in the human gastrointestinal tract. The major site of microbial breakdown of dietary polysaccharides, which also support the highest densities of bacteria is the large intestines in humans. Examples of cultured polysaccharide-degrading species are shown for these sites, together with the phylum to which they belong (Firmicutes or Bacteroldetes) and their characteristic polysaccharide-utilizing abilities. C: cellulose, I: Inulin, S: Starch, X: Xylan Note: Adapted from Flint, H., Bayer, E., Rincon, M., Lamed, R., & White, B. (2008). Polysaccharide utilization by gut bacteria: potential for new insights from genomic analysis. Nature Reviews Microbiology Volume 6, doi: /nrmicro1817

Why Gut Bacteria is Important Associated with: Epithelial and mucosal immunity 2 – Maintains immunoglobins that fight pathogenic bacteria Anti-inflammatory effect on intestinal cells 10 Competes with pathogenic bacteria 10 – Creates hostile environment for colonization Breakdown of polysaccharides that human enzymes can not 4

Gluten Containing Foods and Fiber Certain polysaccharides can not be digested by humans, gut bacteria digest them for us 1,10 – Ex: cellulose and hemicellulose This is their main food source Cellulose and hemicellulose are found in dietary fiber 7 – Insoluble fiber more easily digested than soluble – Insoluble fiber contains more cellulose and hemicellulose Without this food, beneficial bacteria die 11

Gluten Containing Foods and Fiber Gluten containing foods contain more fiber Gluten containing foods: – Wheat (and its derivatives) – Barley – Rye – Triticale – Bulgur Exception: buckwheat and oats – Debatable as to its gluten free status due to processing facility cross contamination

Gluten Containing Foods and Fiber * * * * * * * * Indicates gluten containing grain Note Adapted from Oldways Preservation Trust Whole Grains Council, (2013). Fiber in Whole Grains. Retrieved from whole-grains

Gluten Free Diet and Gut Bacteria Gluten free (GF) diet is the complete elimination of gluten containing foods Reasons for adhering to a GF diet: – Celiac Disease A chronic intestinal inflammatory disorder due to immune response to dietary gluten – Gluten intolerance – Perceived health benefits

Gluten Free Diet and Gut Bacteria Correlation between gluten free diet and decline in beneficial gut bacteria 1,3 Current research – GF diets show an overall decrease in polysaccharides 11 Studies conducted: – Healthy adults without disease on GF diet 1 – Treated and untreated children with Celiac Disease 2

Current Research Results In healthy adults after GF diet 1 : – Increase in gram-negative bacteria Bacteria associated with negative health effects – Decrease gram-positive bacteria Bacteria that supports healthy intestinal function Statistically significant (P<0.05) – Decrease in beneficial gram-positive Bifidobacterium (P<0.020) Lactobacillus (P<0.001) – Increase in harmful gram-negative Escherichia coli (P<0.003) Enterobacteriaceae (P<0.005)

Current Research Results Treated and untreated children with Celiac Disease 2 : Similar results to healthy adults – Increase in gram-negative, decrease in gram-positive bacteria Statistically significant (P<0.05) – Decrease in beneficial gram-positive Bifidobacterium Highest in healthy controls, lowest in untreated

Current Research Results Note: Adapted from De Palma, G., Nadal, I., Medina, M., Donat, E., Ribes-Koninckx, C., Calabuig, M., & Sanz, Y. (2010). Intestinal dysbiosis and reduced immunoglobulin-coated bacteria associated with coeliac disease in children. BMC Microbiology, 10:63. doi: / Treated and untreated children with Celiac Disease

Conclusions GF diet overall decreases gram-positive bacteria May become susceptible to intestinal problems and pathogenic infection due to gut flora imbalance For those without gluten issues: – Long term GF diet is not recommended in accordance with research that has shown its negative effect on overall gut bacteria. GF diet necessary for those with Celiac Disease: – Human body’s negative immune response to gluten – Long term benefit outweighs the risk

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