GlutN – Understanding non-coeliac gluten/wheat sensitivity from plant to consumer

Background and objectives of the study

© Le point sur le gluten, Intercéréales

Gluten consumption can cause allergies, coeliac disease (also known as ‘gluten intolerance’) and non-coeliac gluten/wheat sensitivity (NCGS), which is still poorly understood. The resistance to digestion of flour proteins, including gluten (also known as storage proteins), is blamed for these three conditions.

NG(/B)NC causes various symptoms after ingesting products containing gluten, and in recent years, the number of people complaining to their doctors and adopting a gluten-free diet has increased. Adopting such an exclusionary diet, which is extremely restrictive as it requires the elimination of common foods such as bread, cakes and pasta from the diet, without proven medical reasons, has raised many concerns within the cereal industry regarding their sales of wheat and wheat products, as well as among health professionals and nutritionists.

In this context of the rise of the ‘gluten-free’ diet and given the difficulty of establishing an objective clinical diagnosis of SG(/B)NC, the GlutN project has developed a translational approach, ranging from the plant (selection) to patients (clinical study) via the study of processing methods.

The GlutN project aims to solve SG(/B)NC through two sets of objectives. The objectives for the ‘field’ component include identifying plant characteristics that influence the in vitro digestibility of bread proteins, which can be used for indirect selection, as well as studying bread-making processes with a view to producing specific breads that would be well tolerated (digested) by ‘hypersensitive’ patients.

For the ‘fork’ component, the objectives are to study whether gluten, which contains digestion-resistant peptides, is the causal factor in SG(/B)NC, to develop biomarkers for objectively diagnosing this condition, and to assess its occurrence.

Ultimately, the aim will be to offer breads that are well tolerated by the patients concerned, either by optimising manufacturing processes or by selecting wheat varieties with more digestible proteins. This work is therefore of great interest in the context of sustainable food production, which highlights the need to increase the proportion of plant proteins at the expense of animal proteins.

"Non-coeliac gluten/wheat sensitivity or gluten hypersensitivity is still poorly understood and has no clinical markers. This situation can be particularly difficult for patients, who are often misunderstood, whether they are affected by gluten or not. We need to find answers for these people. This project is extremely interesting and makes a significant contribution to advances in research into gluten tolerance," says Aloys Tack, communications manager at Intercéréales and responsible for promoting the GlutN project.

Digestion of bread proteins: what roles do wheat variety and manufacturing process play?

Initially, an in-depth analysis of 75 varieties of wheat, both ancient and modern (we defined 1960 (the period of the green revolution) as the boundary between ancient and modern material), grown in two locations and genotyped, was undertaken. A sample of 17 varieties representative of the variability (including ancient and modern varieties) of the 75 was baked into bread using a standardised yeast method by Dijon Céréales (Cérélab). The in vitro digestibility of the proteins in these breads, observed after 2 hours of digestion, showed genetic variability. Certain wheat varieties therefore produce bread that is more or less digestible, with no differences related to the age of the plant material. The partial digestibility (as measured after 2 hours of digestion) of bread proteins is similar between old and recent varieties, with no statistically significant difference.

Furthermore, this research has shown that protein digestibility is positively linked to protein content and to the technological properties of the dough. It is also linked to protein composition, either positively or negatively depending on the class of protein considered. The characteristics of gluten (e.g. polymer size) show no link with this digestibility. These results therefore suggest that digestibility can be improved indirectly. Relationships between certain genetic distances and digestibility have also been observed.

‘There are variables that positively or negatively influence digestibility. In short, it is possible to select varieties to improve the partial digestibility of bread proteins, based on these variables measured on the plant or on the flour. Perhaps we could even hope to develop molecular markers to improve this digestibility through marker-assisted selection.’s, summarises Catherine Ravel, INRAE research engineer in the Biology and Plant Improvement Department and project coordinator.

Based on this preliminary work, in collaboration with Dijon Céréales, four varieties were selected and baked using two different processes for a more detailed study. Electron microscopy revealed differences in the structure of the amyloprotein matrix of these breads depending on the variety and process used. These results need to be explored further. In vitro chewing and digestion studies show that sourdough breads do not have the same characteristics as yeast breads. In addition, metabolomic analysis of gastric digestion samples allows the varieties and processes to be distinguished.

This approach was supplemented by a clinical study conducted in collaboration with the Clermont-Ferrand University Hospital, involving tests on ‘hypersensitive’ individuals.

And in humans? From an epidemiological study to a clinical study to examine the role of gluten in SG(/B)NC and detect diagnostic markers.

The results of the epidemiological study conducted by the EREN center based on the NutriNet cohort made it possible to establish the profile of people who exclude gluten without being celiac or allergic and to estimate that the prevalence of SG(/B)NC in the French adult population reached 3%.*

The clinical study brought together a cohort of 19 patients who alternated between two “clone” diets, one with gluten (8 g of gluten per day) and the other without, according to a double-blind experimental design (i.e., neither the doctor nor the patient knew which diet was being administered). To ensure that the two diets could not be identified (as far as possible), gluten-containing and gluten-free products were carefully selected to be as similar as possible. During each phase of the diet, patients recorded their symptoms using a scale specially adapted by Dr. Bouteloup. The aim of this study was to determine whether gluten is indeed responsible for SG(/B)NC. Urine and blood samples were also taken at the end of each diet phase to detect possible markers of sensitivity, which could then be used as a tool for objective diagnosis. Currently, the scoring scale does not allow for differentiation between diets. However, we must wait for the results of further analyses before concluding that gluten is not the cause of SG(/B)NC.

In a second phase, if the role of gluten in the symptoms of “hypersensitive” patients is confirmed, they should have been invited to test the bread identified as being the most digestible versus the least digestible, both in terms of the variety of wheat used and the recipe employed. The long-term objective was to propose dietary solutions that are better tolerated by these patients.

This comprehensive approach, combining laboratory analyses and clinical studies, aimed to shed light on SG(/B)NC and pave the way for dietary solutions better suited to patients' needs.

Catherine concludes: "Wheat is a staple food for humans. Consequently, its proteins should not be overlooked, as they will play an increasingly important role in a context where there is consensus on the need to consume more plant proteins. To produce protein, wheat needs nitrogen. Therefore, no aspect should be overlooked, such as agronomy or genetics, in order to maintain the yield, content, and quality of grain protein with less fertilizer. It is also essential to improve the health quality of these proteins by continuing to work on issues of intolerance in the broadest sense, as well as on their digestibility and their contribution of essential amino acids, including lysine, which is their weak point."