Inclusion criteria for patients
- Signed informed consent
- Fulfilled Rome III diagnostic criteria for IBS, and frequency of IBS pain or discomfort for at least 2 days a week in the last 12 weeks
- Age: 18-65 years
Exclusion criteria for patients
- High proportion of butyrate-producing microbiota in fecal samples
- Known organic gastrointestinal disease (e.g. IBD)
- Previous complicated gastrointestinal surgery
- Non-gastrointestinal malignancy
- Dementia, severe depression, major psychiatric disorder, or other incapacity for adequate cooperation
- Females who are pregnant or breast-feeding
- Severe endometriosis
- Antimicrobial treatment 4 weeks prior to first screening visit
- Antimicrobial prophylaxis (eg. acne, urinary tract infection)
- Regular consumption of probiotic products 4 weeks prior to randomization
- Recently (within the last 3 months) diagnosed lactose intolerance
- Celiac disease
- Abuse of alcohol or drugs
- Any clinically significant disease/condition which in the investigator's opinion could interfere with the results of the trial
Inclusion criteria for donors
- Signed informed consent
- High-butyrate producing microbiota in fecal samples
- Age: 18-65 years
Exclusion criteria for donors
- Known organic gastrointestinal disease (e.g. IBD, IBS, chronic diarrhea or constipation)
- Gastrointestinal malignancy or polyposis
- History of major gastrointestinal surgery (e.g. gastric bypass)
- Eosinophilic disorders of the gastrointestinal tract
- Current communicable disease (e.g. upper respiratory tract infection)
- Known or high risk of infectious diseases such as HIV, hepatitis A, B or C
- Non-gastrointestinal malignancy
- Dementia, severe depression, major psychiatric disorder, or other incapacity for adequate cooperation
- Comorbidities such as metabolic syndrome, autoimmune diseases, allergies
- Chronic pain syndromes (eg. chronic fatigue syndrome, fibromyalgia)
- Severe or morbid obesity
- Use of immunosuppressive or chemotherapy agents
- Antimicrobial treatment or prophylaxis within the last 6 months
- Females who are pregnant or breast-feeding
- Known clinically significant abnormal laboratory values
- Participation in high-risk sexual behaviors
- Abuse of alcohol or drugs
- Tattoo or body piercing within the last 6 months
- Travel to areas with endemic diarrhea during the last 3 months
- Positive stool testing for C. difficile toxin, ova, parasites, Giarda antigen, cryptosporidium antigen