Inclusion Criteria:  IBS patients that meet the Rome IV criteria + additional criteria specific for the diarrhea-predominant subtype, based on the most frequent self-reported stool types using the Bristol stool chart Male and female adults, aged 18-70 years; Having a Body Mass Index (BMI) between 18.5 and 30 kg/m2; Willing to keep a stable dietary pattern throughout the study.  Exclusion Criteria:  Having a disease that may interfere with the outcomes of this study, such as a known autonomic disorder, inflammatory bowel disease, coeliac disease, cancer, dialysis patients, chronic kidney failure, depression or hypothyroidism. History of intestinal surgery (excluding appendectomy or cholecystectomy) or endometriosis. Use of medication that can interfere with the study outcomes, including codeine and antibiotics, as judged by the medical supervisor. Use of anticoagulants (as curcumin has inhibitory effects on platelet aggregation). Use of prebiotics and/or probiotics (should be stopped 4 weeks before the start of the study) and infrequent use of other supplements dedicated to bowel function improvements. Having swallowing problems with pills/capsules. Having a cow's milk allergy or other food allergies. If applicable: currently pregnant or breastfeeding, or intending to become pregnant during the study. Participation in another clinical trial at the same time. Student or employee working at Food, Health and Consumer Research from Food and Biobased Research, or Department of Human Nutrition & Health, Wageningen University. Alcohol intake ≥ 14 (women) or ≥ 28 (men) glasses of alcoholic beverages per week. Smoking and abuse of illicit drugs, soft drugs, and/or nitrous oxide.