The investigators have in a previous study included IBS patients for treatment with a starch- and sucrose reduced diet (SSRD). The investigators found a great improvement of symptoms. The investigators gene-tested those patients, and now have the full identification of all functional variants encoding sucrase-isomaltase enzymes.~The investigators will invite patients from this previous study with normal genes and functional variants of genes. The patients will come fasting over night to the department of clinical research. The participants will ingest 75 g sugar dissolved in 0.8 dl water and flavored with lemon, to ingest during 5 minutes. After that, glucose will determined repeatedly up to 2 hours afterwards. At the same time, the participants have to assess their gastrointestinal sympotms on visual analogue scales (VAS).~The investigators will compare the raise in b-glucose and symptoms between the groups of patients, divided into gene expression.
The investigators know that many patients with irritable bowel syndrome (IBS) have functional variants of genes coding for sucrase-isomaltase enzymes. The investigators will now examine whether these functional variants are associated with defect degradation of sucrose and associated gastrointestinal symptoms