Gluten sensitivity influenced by negative expectations

A psychological effect may be a factor in people experiencing a physical reaction to eating gluten, a protein found in wheat, rye and barley that can cause abdominal discomfort.

Scientists at the University of Leeds and Maastricht University studied a group of 80 people who self-reported they were sensitive to gluten but did not have coeliac disease.

The participants were split into groups and told they would be consuming bread with gluten or bread that was gluten-free.

In half the cases, that was true. In the other cases, the opposite happened: those who thought they were eating gluten-free bread were given bread with gluten and those who thought they were eating bread with gluten consumed gluten-free bread.

The results were unequivocal: people who thought they were eating bread containing gluten reported more gastrointestinal symptoms, whilst those who thought their food was gluten-free reported fewer symptoms.

Expectations influence symptoms

Professor Louise Dye from the School of Food Science and Nutrition led the Leeds arm of the study. She said: “In all of the groups, people’s expectations influenced whether or not they reported symptoms after eating.

“Our study shows that the expectation that gluten causes gastrointestinal complaints plays a crucial role in whether people experience these symptoms.”

Marlijne de Graaf, from Maastricht University who ran the study in the Netherlands, said: ‘In this research, we see a so-called nocebo effect when people eat gluten.

“If people expect gluten to produce negative effects, they experience symptoms, even if it turns out afterwards that they were not eating gluten.

“Although the cause is partly ‘in the mind’, this does not mean that the symptoms are not real.”

Interaction between the brain and intestines

These results, published in the journal The Lancet Gastroenterology and Hepatology, suggest a direct interaction between the brain and intestines, the so-called gut-brain axis.

The researchers now want to concentrate on unravelling the mechanisms which determine the importance of expectation and exposure along the gut-brain axis.

Daisy Jonkers, Professor of Intestinal Health at Maastricht University and who led the study in the Netherlands, said: “Due to the influence of interactions between the brain and the intestines, people can genuinely experience symptoms such as stomach ache, bloating or diarrhoea after eating gluten.

“The cause of these complaints is not only eating gluten, so a gluten-free diet isn’t the only solution.’

To treat this problem, the researchers want to conduct further studies on the influence of the brain on the development of bowel complaints.

“For example, we’d like to know exactly which areas in the brain are involved,” added Professor Jonkers. “We also want to find out what substances play a role in the communication between the brain and the gut, and whether people might respond differently to them.

“It is also quite possible that some people cannot tolerate wheat products because of substances in wheat other than gluten and that there is indeed something in wheat that can lead to overstimulation of the immune system, for example, or excessive production of gas by the gut flora.”

The paper, titled 'The effect of expectancy versus actual gluten intake on gastrointestinal and extra-intestinal symptoms in non-coeliac gluten sensitivity: a randomised, double-blind, placebo-controlled, international, multicentre study,’ can be downloaded from the journal website.