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Gluten sensitivity influenced by negative expectations
Self-reported gluten intolerants experienced symptoms even when eating gluten-free food if they believed it contained the protein
Symptoms of gluten sensitivity are partly to do with people’s expectations, if coeliac disease and wheat allergy have been excluded as causes.
Research at the universities of Maastricht and Leeds, with Wageningen University and some input from Rothamsted Research, shows that the expectation that gluten causes gastrointestinal complaints plays a crucial role in whether or not people experience these symptoms.
This indicates a direct involvement of the interaction between the brain and the intestines – the so-called gut-brain axis – in the experience of complaints after ingesting gluten. As yet, knowledge on the topic remains limited. The results of the study were recently published in the scientific journal The Lancet Gastroenterology and Hepatology.
Gluten
A growing number of people are reducing their gluten intake due to self-reported digestive complaints, despite the fact that coeliac disease and wheat allergy have been ruled out. The cause of their symptoms is often unclear. The researchers therefore wanted to investigate the effects of expectations on symptoms experienced after gluten intake. More than 80 subjects with self-reported gluten sensitivity took part in a psychological study and were divided into four groups. The results were unequivocal: people who thought they were eating food containing gluten reported more symptoms, while those who thought their food was gluten-free reported fewer symptoms.
In reality, the food given to half of each group contained gluten, while for the other half it was gluten-free. In all of the groups people’s expectations played a prominent role in whether or not they reported symptoms after eating. ‘In our research, we see a so-called nocebo effect when people eat gluten,’ says researcher Marlijne de Graaf. ‘If people expect gluten to produce negative effects, they experience symptoms, even if it turns out afterwards that they weren’t actually eating gluten. Although the cause is partly “in the mind”, this doesn’t mean that the symptoms are not real.’
Gut-brain axis
The results of this study indicate a clear involvement of the interaction between the brain and the intestines in gluten sensitivity, a subject on which knowledge is as yet limited. The researchers therefore now want to concentrate on unravelling the mechanisms that determine the importance of expectation and exposure along the gut-brain axis. ‘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,’ says Daisy Jonkers, professor of Intestinal Health at Maastricht University. ‘But 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,” says Jonkers, “and 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’s also quite possible that some people can’t 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. This is also something we’d like to investigate.’
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Contacts
Prof. Peter Shewry
Botanist
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