The Christchurch IBS cohort to investigate mechanisms for

INTERVENTION: ‐ Oral intake of two SunGold Kiwifruit daily, for a minimum of three weeks and a maximum of four weeks, in a randomised, single blinded, cross‐over study. ‐If participant is unable to come to the clinic after exactly 4 weeks, an earlier visit (up to 7 days before the end of week 4) is allotted to prevent participants from running out of intervention materials. ‐ Study duration is 2 weeks baseline, minimum of 3 weeks intervention I, minimum of three weeks washout, minimum of three weeks intervention II, two weeks follow up. ‐ Kiwifruits will probably have a weight of 50‐70 g (no information from italian growers yet) ‐ Fruit will be provided by the research team in bulk ‐ The participants will take the interventions at home ‐ leftover fruit will be counted to measure adherence ‐ Biological samples (blood, breath, urine stool) will be collected at baseline, after intervention one, after wash out, after intervention two, and after follow up. ‐ Samples will be analysed as during the COMFORT study (targeted and untargeted metabolome, transcripome, microbiome, bile acids, inflammation markers, neurotransmitters). ‐ Questionnaires (as used for the COMFORT cohort) will be filled out by participants throughout the 16 weeks and used to collect data on mental health, socioeconomic status, lifestyle, gastrointestinal and overall health, food and bowel movement diaries. ‐ The data generated with the questionnaires will be correlated to the data of the biological samples, to the group they are in, as well as to intervention they received at each phase, to see how the interventions affects each group, if the interventions have different effects and outcomes, and if changes occur in any of the domains during non‐intervention phases as well. CONDITION: Constipation Irritable Bowel Syndrome PRIMARY OUTCOME: Composite outcome: feasibility of the novel cohort as basis for clinical studies in regards to the burden in answering questionnaires and visiting the clinic . ; We will ask the participants how comfortable they were with the large numbers of questionnaires they have to fill out, how hard it was for them to reach the clinic, and what they would like to have changed if they would participate in a similar study. Feasibility of the novel cohort as basis for clinical studies in regards to completion (how many participants have enrolled vs how many participants finish the study by visiting the clinic for the follow‐up visit) Feasibility of the novel cohort as basis for clinical studies to investigate novel and alternative dietary treatments for digestive function such as high value food and nutraceuticals in regards to recruitment. ; The study will be feasible if we are able to enroll 80% of participants before the cut‐off point, which is the 14th of December 2018. SECONDARY OUTCOME: A change in GSRS ratings in the FC/IBS group with both interventions ; GSRS is a questionnaire, which is filled out by participants weekly. A change in complete spontaneous bowel movements in FC/IBS‐C group during the interventions in comparison to baseline, wash out, and follow up. ; Assessed daily with the daily bowel movement diary. Feasibility of the novel cohort as basis for clinical studies in regards to adherence to protocol. ; This is a composite outcome. INCLUSION CRITERIA: Healthy volunteers without FC/IBS for the control group, and presence of functional constipation according to ROME IV Diagnostic Criteria or presence of mild IBS‐C based on the Rome IV Diagnostic Criteria for the IBS/FC group. ; We measure vitamin C to test if they ate the kiwifruit. We check if they have filled out all questionnaires, or if they left some of them blank. We weigh the psyllium they bring back to see if they may have taken it or stopped during the time. We write up if participants stop showing up during the 16 weeks. We used participants without IBS/FC for the COMFORT cohort, to be able to compare data (biological and questionnaire) from a "healthy" digestion to "disordered" digestion. These are the two groups. However, in this feasibility study, both groups will be analysed in regards to baseline , during both interventions, and during wash out and follow up, since we are interested how digestion may change in both groups over time in a future clinical trial.