The investigators hypothesize that dietary treatment will improve the experience of gastrointestinal symptoms, pain and quality of life in patients with endometriosis-related irritable bowel syndrome. The aim of this first randomized, placebo controlled pilot study investigating patients with both endometriosis and IBS, is to test the application of a low FODMAP diet and a placebo diet for endometriosis-related IBS-like symptoms in order to stablish a platform for a randomized controlled study. Thus, the primary aim of this pilot study is to investigate the applicability of a placebo diet in patients with endometriosis and to investigate the compliance in both intervention group and control group. In addition, the aim is to investigate whether the participants find the diet manageable and whether they are able to identify the placebo diet.