The effect of the gluten-free diet on the gut

In this study, ten volunteers without coeliac disease (with no history of digestive problems or signs of malabsorption) were asked to follow a gluten-free diet by replacing foods that contained gluten with foods that were gluten-free (less than 20 parts per million of gluten).

Effect on gut bacteria

Faecal samples were collected from each adult and the bacteria levels were measured. The introduction of the gluten-free diet resulted in a reduction in bacteria generally regarded as beneficial for health, such as bifidobacterium and lactobacillus and an increase in harmful bacteria such as Escherichia coli and total enterobacteriaceae.

The reduction in healthy bacteria could be due to lower intakes of polysaccharides found in starchy foods, like  bread and pasta. Polysaccharides usually reach the distal part of the colon undigested and are an energy source for beneficial bacteria.

However, gluten-free foods like potato and rice also contain polysaccharides.  The reduction in healthy bacteria could be explained by the change in the diet resulting in a reduction of carbohydrate rich foods.

Effect on immune activity of gut bacteria

To measure immune function blood samples were taken from four individuals.

The production of pro-inflammatory cytokines TNF and IFN-y was found to be lower after following the gluten-free diet. This means the gluten-free diet could result in the immune system being suppressed.

The immune-suppressive effects of the gluten-free diet may be partly beneficial for people with coeliac disease in reducing the immune response to gluten. However, this could also reduce defense against harmful antigens.

Further research

Although this is a preliminary short-term intervention study, bacterial changes are similar to those detected previously in children on a gluten-free diet in a long-term intervention study.

This study has assessed the effect of GFD on healthy population and might not reflect the same findings in coeliac patients. Also, the number of the study group is very small (only 10). Whatever would be the effect of GFD on immune function and microbiota, this shouldn't bring any doubt on the positive and preventive effect of GFD on improving the clinical symptoms and preventing the complications in coeliac patients.

Further research is required to look at the effect of the gluten-free diet on the gut and the immune system. Other research projects should consider the effect the gluten-free diet can have on the bacteria in the gut and how this could be a confounding factor.

References

Palma GD, Nadal I et al (2009) Effects of a gluten-free diet on gut microbiota and immune function in healthy adult human subjects. British Journal of Nutrition