Non-coeliac gluten sensitivity: piecing the puzzle together

What is gluten?

Gluten is the main storage protein of wheat grains. Gluten is a complex mixture of hundreds of related but distinct proteins, mainly gliadin and glutenin. Similar storage proteins exist as secalin in rye, hordein in barley, and avenins in oats and are collectively referred to as "gluten." The objective was to discuss the biochemical and functional properties of the gluten proteins, including structure, sources, and dietary intakes. Literature was reviewed from food science and nutrition journals. The gluten protein networks vary because of different components and sizes, and variability caused by genotype, growing conditions, and technological processes. The structures and interactions of this matrix contribute to the unique properties of gluten. The resulting functions are essential to determining the dough quality of bread and other baked products. Gluten is heat stable and has the capacity to act as a binding and extending agent and is commonly used as an additive in processed foods for improved texture, moisture retention, and flavor. Gliadin contains peptide sequences that are highly resistant to gastric, pancreatic, and intestinal proteolytic digestion in the gastrointestinal tract. The average daily gluten intake in a Western diet is thought to be 5-20 g/day and has been implicated in several disorders. Gluten containing grains (wheat, rye, barley, and oats) are important staple foods. Gluten is among the most complex protein networks and plays a key role in determining the rheological dough properties.

The broad spectrum of celiac disease and gluten sensitive enteropathy

The celiac disease is an immune chronic condition with genetic transmission, caused by the intolerance to gluten. Gluten is a protein from cereals containing the following soluble proteins: gliadine, which is the most toxic, and the prolamins. The average prevalence is about 1% in USA and Europe, but high in Africa: 5.6% in West Sahara. In the pathogenesis several factors are involved: gluten as external trigger, genetic predisposition (HLA, MYO9B), viral infections, abnormal immune reaction to gluten. Severity is correlated with the number of intraepithelial lymphocytes, cryptic hyperplasia and villous atrophy, as well as with the length of intestinal involvement. The severity is assessed according to the Marsh-Oberhuber staging. Diagnostic criteria are: positive serological tests, intestinal biopsy, the reversal after gluten free diet (GFD). Beside refractory forms, new conditions have been described, like the non celiac gluten intolerance. In a time when more and more people adhere to GFD for nonscientific reasons, practitioners should be updated with the progress in celiac disease knowledge.

[Non-allergic gluten sensitivity. A controversial disease - or not yet sufficiently explored?]

The avoidance of wheat, gluten and other cereal products is a growing phenomenon in industrialized countries. The diagnostic criteria of celiac disease and of food allergy to wheat flour and/or other cereals are clearly defined. Only about 0.5-25 % of the population are affected from both of these immunological diseases.Nevertheless, there exists a significantly greater proportion of people reporting at least subjectively significant complaints and quality of life improvements after switching to a wheat- or gluten-free diet. Celiac disease or wheat allergy cannot be detected in these individuals on the basis of established criteria. The absence of clear diagnostic autoimmune or allergic criteria in these wheat sensitive patients has resulted in the description of non-celiac gluten sensitivity.It is clinically detectable in only very few individuals and may manifest with either intestinal, extra-intestinal or neurovegetative and psychosomatic symptoms, respectively. However, non-celiac disease gluten sensitivity has to be differentiated critically from irritable bowel syndrome, carbohydrate malassimilation, postinfectious conditions and psychosomatic diseases.Pathophysiologically, non-celiac disease gluten sensitivity is still poorly characterized; several non-immunological mechanisms are discussed to contribute to non-celiac gluten sensitivity. These include the effects of fructo- and galacto-oligosaccharides, of trypsin inhibitors of amylase, and wheat lectin agglutinins, which may influence or modulate intestinal permeability and/or a non-specific immune or effector cell degranulation within the gastrointestinal tract. In addition, further metabolic effects with direct or indirect influence on the intestinal flora are currently discussed.In addition to subjectively reported changes in symptoms that may affect variably intestinal, as well as extra-intestinal and/or neuropsychiatric symptoms, some studies suggest that there is little reproducibility of complaints from gluten exposure. For a definitive diagnosis of non-celiac gluten sensitivity, structured (blinded) challenge tests with wheat or gluten are mandatory as well as re-challenge after a defined time of gluten avoidance to establish non-celiac disease gluten sensitivity as a persistent disease entity.

[Successes and unsolved problems in the study of celiac disease]

The review gives current views on the problem of celiac disease (gluten enteropathy). It presents the pathogenetic components of pathology development, associations with the specific features of the microflora in different parts of the gastrointestinal tract, as well as groups at risk for this pathology. The idea on other types of gluten intolerance is briefly given. Current elaborated approaches to gluten enteropathy therapy are provided.

Do we need to worry about eating wheat?

Wheat is a staple food throughout the temperate world and an important source of nutrients for many millions of people. However, the last few years have seen increasing concerns about adverse effects of wheat on health, particularly in North America and Europe, with the increasing adoption of wheat‐free or gluten‐free diets. This relates to two concerns: that wheat products are disproportionally responsible for increases in obesity and type 2 diabetes and that wheat gluten proteins cause a range of adverse reactions, including allergies, coeliac disease and ‘non‐coeliac gluten sensitivity’. The first concern has been refuted in previous publications, and we therefore focus on the second here. Current evidence indicates that allergy to ingested wheat and coeliac disease (and related intolerances) each occur in up to 1% of the population. The extent to which their prevalence has increased is difficult to quantify due to improved diagnosis and increased awareness. However, neither appears to be increasing disproportionally when compared with other immunologically mediated adverse reactions to food. Other adverse reactions to wheat are more difficult to define as their mechanisms are not understood and they are therefore difficult to diagnose. In particular, ‘non‐coeliac wheat sensitivity’ has been reported to occur in 6% or more of the population in the US. However, the application of more rigorous diagnostic criteria is likely to give substantially lower estimates of prevalence. It is therefore unlikely that the health of more than a small proportion of the population will be improved by eliminating wheat or gluten from the diet. In fact, the opposite may occur as wheat is an important source of protein, B vitamins, minerals and bioactive components.

Diet low in FODMAPs reduces symptoms of irritable bowel syndrome as well as traditional dietary advice: a randomized controlled trial

BACKGROUND & AIMS

A diet with reduced content of fermentable short-chain carbohydrates (fermentable oligo-, di-, monosaccharides, and polyols [FODMAPs]) has been reported to be effective in the treatment of patients with irritable bowel syndrome (IBS). However, there is no evidence of its superiority to traditional dietary advice for these patients. We compared the effects of a diet low in FODMAPs with traditional dietary advice in a randomized controlled trial of patients with IBS.

METHODS

We performed a multi-center, parallel, single-blind study of 75 patients who met Rome III criteria for IBS and were enrolled at gastroenterology outpatient clinics in Sweden. Subjects were randomly assigned to groups that ate specific diets for 4 weeks-a diet low in FODMAPs (n = 38) or a diet frequently recommended for patients with IBS (ie, a regular meal pattern; avoidance of large meals; and reduced intake of fat, insoluble fibers, caffeine, and gas-producing foods, such as beans, cabbage, and onions), with greater emphasis on how and when to eat rather than on what foods to ingest (n = 37). Symptom severity was assessed using the IBS Symptom Severity Scale, and patients completed a 4-day food diary before and at the end of the intervention.

RESULTS

A total of 67 patients completed the dietary intervention (33 completed the diet low in FODMAPs, 34 completed the traditional IBS diet). The severity of IBS symptoms was reduced in both groups during the intervention (P < .0001 in both groups before vs at the end of the 4-week diet), without a significant difference between the groups (P = .62). At the end of the 4-week diet period, 19 patients (50%) in the low-FODMAP group had reductions in IBS severity scores ≥50 compared with baseline vs 17 patients (46%) in the traditional IBS diet group (P = .72). Food diaries demonstrated good adherence to the dietary advice.

CONCLUSIONS

A diet low in FODMAPs reduces IBS symptoms as well as traditional IBS dietary advice. Combining elements from these 2 strategies might further reduce symptoms of IBS. ClinicalTrials.gov ID NCT02107625.