Many people now exclude gluten from their diet, despite not having coeliac disease or a wheat allergy, because they experience symptoms such as bloating, diarrhoea, constipation, headaches and fatigue. However, there is a lack of knowledge about the underlying mechanisms. “Not enough is known about the negative health effects in people who experience gluten or wheat sensitivity. Wheat, especially wholegrain wheat, is an important dietary component because wholegrains are so beneficial for health,” says Daisy Jonkers. In the nocebo study, the research team studied people’s negative expectations of gluten and how this affects perceived symptoms. The nocebo effect is the opposite of the placebo effect, which means that negative expectations exacerbate or even create symptoms. The study was a randomised double-blind study in which 83 people, aged 18 to 70, with selfperceived negative problems with gluten intake, participated. They were first tested to rule out coeliac disease, wheat allergy or other gastrointestinal disease and then randomly assigned to one of four study groups:

A. Expecting to consume bread with gluten and actual intake of bread with gluten
B. Expecting to consume gluten-free bread but actual intake of bread with gluten
C. Expecting to consume bread with gluten but actual intake of gluten-free bread
D. Expecting to consume gluten-free bread and actual intake of gluten-free bread

Groups B and C did not know that they received bread with gluten or gluten-free bread, respectively. The groups followed their prescribed diet for one week. Gastrointestinal symptoms were measured using self-assessment with the visual analogue scale before breakfast and then every hour for eight hours. The results showed that group A, who expected to eat gluten and who also ate bread with gluten, reported significantly more symptoms than the other groups. Their symptoms were primarily bloating, stomach pain and diarrhoea. “The two groups who did not expect to eat gluten had the lowest level of perceived symptoms, whether they were given gluten or not,” says Jonkers. She emphasises that the research team takes the symptoms very seriously and the results indicate that the gut-brain axis is involved.

...many people can recognise the feeling of stomach ache before a difficult exam. The question is why this happens.

“I’m sure many people can recognise the feeling of stomach ache before a difficult exam. The question is why this happens. The connection between the brain and the gut is a hot research topic right now. We know that signalling occurs in both directions, that the gut microbiota can be influenced by the brain and that they can send information to the brain – it would be interesting to study whether some people have heightened sensitivity to this signalling,” concludes Jonkers.

Text: Karin Janson
Illustration: Lene Due Jensen
Photo: Marcel van Hoorn