Inclusion Criteria:

• - Develops of self-reported GI symptoms after a single intake of bread or gluten- containing products; - Age between 18-70 years; - Avoiding or restricting gluten-containing foods for at least 1 week before start of as well as during the study (based on a gluten-free dietary compliance questionnaire of Biagi et al.

(only group 2, 3 and 4 of the Biagi will be eligible);

• - Asymptomatic or only mildly symptomatic (overall) GI symptoms score with VAS < 30mm) while on the gluten-free/gluten-restricted diet; - Must have a freezer (-18ºC) to store the study breads during the study; - Willing and able to give written informed consent and to understand, participate and comply with the research project requirements.

Exclusion Criteria:

• - Medical history of coeliac disease, wheat allergy, inflammatory bowel disease, presence of an organic gastrointestinal (GI) disease (such as inflammatory bowel disease) or other disease which may interfere with NCGS symptoms (upon judgment of the physician-clinical investigator (Dr.

Keszthelyi, Gastroenterologist MUMC+));

• - Previous major abdominal surgery or radiotherapy interfering with gastrointestinal function: - Uncomplicated appendectomy, cholecystectomy and hysterectomy allowed unless within the past 6 months; - Other surgery may be allowed based upon judgment of the physician-clinical investigator (Dr.

Keszthelyi, Gastroenterologist MUMC+), who will decide on inor exclusion based upon the surgery applied;

• - Use of medication potentially influencing gastrointestinal function and/or NCGS symptoms is allowed, provided that dosing has been stable for ≥ 1 month before enrolment; - Use of antibiotics within 90 days prior to the study; - Administration of probiotic, prebiotic supplements, investigational drugs or participation in any scientific intervention study, which may interfere with this study (to be decided by the principle investigator), in the 14 days prior to the study; - Use of immunosuppressive drugs within 90 days before enrolment; - Excessive use of alcohol (>15 alcoholic units per week), or other drugs; - Plan to lose weight or follow a specific weight loss diet within the study period; - Current malignancy; - Pregnancy or breastfeeding; - Participation in any scientific intervention study, which may interfere with this study; - Insufficient fluency of the Dutch language.

Arms

Active Comparator: Bread types 1 & 2

Daily consumption of 5 slices of allocated bread type for 3 consecutive days.

Active Comparator: Bread types 3 & 4

Daily consumption of 5 slices of allocated bread type for 3 consecutive days.

Active Comparator: Bread types 5 & 6

Daily consumption of 5 slices of allocated bread type for 3 consecutive days.

Interventions

Dietary Supplement: - Different types of bread

Three-arm randomized cross-over study. All subjects start with a run-in period of 3 days, thereafter they will receive two different types of bread in a randomized order for 3 consecutive days, with a wash-out period of 11 days in between. After each period, biological samples will be collected.