Probiotics efficacy is mainly assessed by subjective endpoints such as the FDA responder rate or global relief, which partly explain contradictory results obtained in clinical trials with probiotic bacteria. Objective biomarkers of IBS will allow to measure the efficacy of probiotics. In the case of IBS-C, serum resolvin-D1 appears to be an interesting candidate due to its non-invasive and discriminating character compared to a healthy population. It is, inversely correlated with the severity of symptoms. Resolvin-D1 modulates the duration and intensity of inflammation by regulating the transcription of cytokines, chemokines and their receptors as well as other proteins involved in inflammation. Resolvin D1 could serve as a predictor of probiotic response based on its baseline value.

Resolvin D1 levels will be measured in patients with IBS-C as defined by the Rome IV criteria before 6 and 12 weeks after supplementation with a mixture of probiotics. The progression of IBS-C symptoms will also be assessed throughout the study.

The correlation with resolvin D1 levels and the severity of IBS symptoms will be investigated. The efficacy of the probiotic mixture in relieving the symptoms of IBS-C will be measured and compared based on the levels of resolvin D1.

Inclusion Criteria:

• Irritable Bowel Syndrome with constipation (IBS-C) according to Rome IV criteria ;
• IBS-SSS between 175-300 in the last 10 days ;
• Have experienced abdominal pain ≥ 40 according to the IBS-SSS questionnaire (abdominal pain item) during the last 10 days ;
• Whose abdominal pain / discomfort has had a significant impact on daily life during the past 10 days (impact ≥2 on a 5-point likert scale (from 0: no impact to 5: extreme impact) ;
• Ability to understand instructions and complete questionnaires Nurstrial APP.
• Affiliate or beneficiary of a social security ;
• Having given their free, informed and written consent.

Exclusion Criteria:

• CPRu > 10 mg/l
• Pregnant or breastfeeding woman, woman planning a pregnancy during the study period ;
• Intolerance or proven food allergy ;
• BMI <18.5 kg / m2 or BMI> 35 kg / m2 ;
• Diagnosis or known history of IBS-D, IBS-M, or unclassified forms of IBS, or other gastrointestinal pathologies ;
• With current first-line IBS-C treatment or second-line treatment ;
• alternative non pharmacological treatment ;
• Drug treatment affecting visceral sensitivity or intestinal transit ;
• dietary modification (exclusion of FODMAPs, prebiotic) or lifestyle ;
• Excessive smoking or drinking ;
• Having or planning bariatric surgery,
• With known pathologies affecting gut function ;
• With a deviant eating behavior,
• Treated with antibiotics in the 3 months preceding inclusion,
• Under legal protection,
• Already included in a clinical trial,
• With severely impaired physical/psychological health may affect study participation.