People with irritable bowel syndrome (IBS), especially those with diarrhea (IBS-D), often describe worsening symptoms after eating certain foods. A structured dietary approach may represent a reliable strategy to improve their symptoms. In this framework, the diet low in oligosaccharides, disaccharides, monosaccharides, and fermentable polyols (FODMAPs - LFD) has been demonstrated to mitigate symptoms and reduce inflammatory status, increase vitamin D content, and affect the lipidomic profile. Unfortunately, adherence to LFD can be somewhat problematic, needing continuous nutritional support. Other dietary approaches with putative beneficial effects have been proposed to overcome these limitations. Among them, Tritordeum-based foods (TBD, bread, bakery products, and pasta) in substitution of other cereals seem to achieve promising results. TBD may represent a valid alternative, with high palatability, especially among Italian patients for whom pasta is considered one of the main assets of dietetic culture and easier to manage in their daily habits. Given these premises, this study aims to evaluate, in a randomized single-blinded controlled trial, the effects of 12-weeks of TBD compared with LFD and dietary advice of the same duration in improving the symptom profile well as the intestinal permeability and reducing putative dysbiosis of IBS-D patients. Along with the clinical study, an evaluation of gluten and proteomic composition will be performed to examine more in detail the intrinsic characteristics of Tritordeum.

A structured dietary approach could represent a reliable alternative strategy to treat patients with functional gastrointestinal disorders such as irritable bowel syndrome (IBS), mainly in its diarrhea variant (IBS-D). It is now well established that many people with IBS often describe worsening symptoms eating certain foods, such as those containing fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). These short-chain carbohydrates are present in some foods, including wheat and beans. They may contribute to different digestive symptoms such as bloating, abdominal pain, and diarrhea due to poor absorption in the small intestine. In this way, FODMAPs are digested by colonic bacteria, releasing gas in the colon.

Furthermore, FODMAPs can act as osmotic agents, increasing the water volume in the stool. In the last years, our group has focused research on the properties of a low FODMAPs diet (LFD) in the clinical management of patients with IBS-D, demonstrating that these patients benefit from a 12 weeks-LFD in mitigating the symptoms, reducing the inflammatory status, increasing the vitamin D content, and affecting the lipidomic profile. Unfortunately, adherence to LFD can be somewhat problematic, needing continuous nutritional support.

Actually, alternative dietary approaches for these disorders may be hypothesized. It is now well established that, beyond non-celiac wheat sensitivity (NCWS), many individuals suffering from IBS-D or generical gluten-related disorders and mainly complainIng of abdominal bloating seem to benefit from removing wheat from the diet.

The multifaceted setting of nutrients in wheat-based foods, other than gluten, could account for the different IBS symptoms. It has already been postulated that some monococcal diploid grain lines, with minimal activation of the innate immunity and a reduced amount of toxic gluten peptides, could be helpful for IBS-D patients. Among them, alternative grains such as Tritordeum seem to achieve good results. Tritordeum is a cereal derived from durum wheat and wild barley hybridization. Originally cultivated with traditional techniques in Spain, it has more recently grown in Apulia, a southern Italy region. Tritordeum grows well with little care, even in adverse conditions. Noteworthy, this cereal has significantly lower levels of gliadins, fewer carbohydrates and fructans, and a higher content of dietary fibers, proteins, and antioxidants than classic wheat. However, the presence of gluten makes this cereal not suitable for celiac patients.

Thus, cereals such as Tritordeum, once further characterized in their proteomic profile and gluten composition, could offer opportunities for an innovative nutritional approach for patients suffering from IBS and, more in general, wheat-related disorders. Our group recently performed a pilot study to investigate the effects of a 12-week diet with Tritordeum-based foods (bread, bakery products, and pasta) in substitution of other cereals on the GI symptoms and the status of the GI barrier in IBS-D patients. This diet proved to reduce the patients' symptoms by affecting intestinal permeability significantly. The purpose of this study is to evaluate, in a randomized controlled trial, the beneficial effects of 12-weeks of TBD compared with LFD or specific advice for IBS of the same duration in improving the symptom profile of IBS-D patients.

Inclusion Criteria:

• Rome IV criteria for IBS diarrhea variant (IBS-D).
• Low-lactose diet is allowed, provided that patients agree to keep this intake constant throughout the study period, except in the case of randomization in the treatment arm with a low-FODMAPs diet.
• The use of probiotic products is permitted, and patients who consume probiotic products must be instructed to continue taking the same amount previously taken throughout the study period.
• The drugs used to treat IBS, including antidepressants, will be admitted provided they are used regularly and have a stable dosage for at least one month prior to inclusion in the study.
• Patients must be willing to change their current diet to participate in the study for the whole study period.

Exclusion Criteria:

• Serious cardiac, hepatic, neurological or psychiatric diseases.
• GI diseases other than IBS (e.g., inflammatory bowel disease, celiac disease) that could explain current symptoms.
• Patients who previously had a low-content diet of particular substances (for example, low FODMAPs content, vegan diet, a gluten-free diet). - This last category of subjects will be able to return to the study provided they suspend the gluten-free diet until the symptoms reappear.

The investigator, but not the patients will know the real identity of the treatment assignment (food preparation and packaging will be unlabelled and not recognizable).