Tolerance to an Artisanal Bread in a Population Intolerant of the Conventional Bread and Study of Associated Markers

Abbreviations:

* GSRS-IBS: Gastrointestinal Symptom Rating Scale for Irritable Bowel Syndrome * GIQLI: Gastrointestinal Quality of Life Index * HADS: Hospital Anxiety and Depression Scale * FSS: Fatigue Severity Scale * LBP: Lipopolysaccharide-Binding Protein

Inclusion Visit (visit 0 \[V0\])

At the inclusion visit (V0) at Avicenne Hospital (Bobigny), participants will receive study instructions and materials. They will have up to 15 days to:

* Complete questionnaires (modified GSRS-IBS, Bristol Stool Scale, GIQLI, HADS, FSS) * Collect a baseline stool sample, stored at -18°C at home until their first hospital visit (V1).

Wash-out phase (Day-15 \[D-15\] to Day 0 \[D0\]):

Participants will follow a gluten-free and low-fructan diet for 15 days. During this period:

* Daily food intake will be recorded in a diary, with meal photos sent to the research team via a dedicated email * On D-8, participants will complete the modified GSRS-IBS and Bristol Stool Scale. * On D-1, participants will perform a 24-hour urine collection after ingestion of lactulose (10g) and mannitol (10g) in 200 mL water, divided into three containers: * First morning urine * 0-5 h collection after sugar ingestion (fasting except water) * 5-24 h collection Stool will also be collected on D-1 and stored at 4°C until V1.

First investigation day (Day 0 \[D0\] - V1):

At 9 a.m., participants arrive the Clinical Research Center (at Avicenne Hospital) with their stool and urine samples.

After completing the questionnaires (modified GSRS-IBS, GIQLI, HADS, FSS, and Bristol Stool Scale), a venous catheter will be inserted for blood sampling.

A 10 mL blood sample will be collected before the test meal. Participants will then consume the test meal (105 g of "artisanal" bread with water).

Postprandial blood samples (2 mL each) will be collected every 30 minutes for 3 hours (total blood volume: 22 mL) The modified GSRS-IBS questionnaire will be completed every hour during the postprandial period If a bowel movement occurs during the visit, the stool sample collected at that time may be used to replace the one collected the previous day.

Intervention phase (D1 to D14):

Participants will continue the same gluten-free, low-fructan diet, with the addition of the "artisanal" bread, which will serve as the sole source of gluten source and the main source of fructans.

* D1: 75 g of bread * D2: 100 g of bread * D3-14: 125 g of bread daily (≈ 8.5 g gluten, \<1.2 g fructans) Bread consumption may be distributed throughout the day. On D8, participants will again complete the modified GSRS-IBS and Bristol Stool Scale.

Second investigation day (D15 - V2):

On D14, participants will repeat the 24-hour urine and stool collection as previously described. On D15, they will return to the research center and undergo the same procedures as V1.

Measurements:

* Questionnaires: modified GSRS-IBS (gastrointestinal symptoms), GIQLI, HADS, FSS. * Blood: LBP (marker of inflammation), zonulin (marker of intestinal permeability), glucose, insulin. * Urine: lactulose and mannitol, with calculation of the lactulose/mannitol ratio as a marker of intestinal permeability. * Stool: microbial community analysis (microbiota) and fecal calprotectin (marker of inflammation). Baseline stool samples (before wash-out phase) will also be used to inoculate an artificial colon model for later investigation of the effects of bread on the microbiota.

• Intensity of gastrointestinal and extraintestinal symptoms [Срок оценки: Scores at Day 0 [D0] and Day 15 [D15]]
• Validity of the modified GSRS-IBS [Срок оценки: Scores of the two questionnaires at Day [D0] and Day [D15]]
• Comparison between volunteers' perceived tolerance of "artisanal" bread and measured tolerance [Срок оценки: Scores at Day 0 [D0] and Day 15 [D15]]
• Clinical profile of response to the "artisanal" bread [Срок оценки: These scores are measured at Day 0 [D0], Day 8 [D8] and Day 15 [D15].]
• Evaluation of intestinal permeability [Срок оценки: Measured on Day D0 [D0] and Day 15 [D15]]
• Evaluation of intestinal inflammation [Срок оценки: Serum LBP : measured on Day 0 [D0] and Day D15 [D15] Fecal calprotectin : measured in stool samples collected at Day-1 [D-1] and Day 14 [D14].]
• Microbiota composition [Срок оценки: Determined in stool samples collected at visit 0 [V0], on Day -1 [D-1] and Day 14 [D14]]
• Tolerance profiles for "artisanal" bread [Срок оценки: From the enrollment (visit 0 [V0]) to the end of the study (Day 15 [D15])]
• Postprandial glucose responses measured after consumption of the test meal ("artisanal bread") [Срок оценки: Measured at 0; 0.5; 1; 1.5; 2; 2.5 and 3 hours after test meal]
• Postprandial insulin responses measured after consumption of the test meal ("artisanal bread") [Срок оценки: Measured at 0; 0.5; 1; 1.5; 2; 2.5 and 3 hours after test meal]
• Substrate oxidation rates [Срок оценки: Measured at 0; 0.5; 1.5 and 2.5 hours after test meal]
• H2 concentrations in exhaled air [Срок оценки: Measured at 0; 0.5; 1; 1.5; 2; 2.5 and 3 hours after test meal]