The study participants will focus on the nutritional therapy and the integrative medical concept taught during their inpatient stay at the clinic for internal and integrative medicine in Bamberg.

Participants will receive no additional blueberry treatment.

The disease severity of UC patients is evaluated via a validated questionnaire that is specific for ulcerative colitis (MAYO-Score): The Mayo Score is the most commonly used scoring system for UC in clinical trials and routine practice. It was developed to standardize the severity of a patient's UC symptoms, which is particularly helpful to assess response to treatment over time. For this study, the partial MAYO-Score is applied, which comprises only the non-invasive components of the full Mayo score. Endoscopic findings are not taken into account. The index considers three clinical parameters, each of which is assigned a score from 0 to 3 leading to a maximum score of 9 points. Clinical response is defined as a decrease of at least 2 points.

The IBD-SI combines items from existing clinician-rated or diary-format inventories. After factor analysis, 38 items were retained on 5 subscales: bowel symptoms, abdominal discomfort, fatigue, bowel complications, and systemic complications. A total score as well as subscale scores will be calculated.

The IBD-Q is the most frequently used questionnaire for disease-specific quality of life in clinical studies on Crohn's disease. It operationalizes quality of life on 4 dimensions (emotional and social impairment as well as bowel-related and systemic symptoms), in addition to a sum score. Answers are recorded on a 7-point Likert scale. High values mean good, low values a reduced quality of life (1=worst score, 7=best score). The total IBD-Q scale ranges from 32 to 224. A score of ≥ 170 can be considered as normal quality of life.

The Short Form 12 Health Survey (SF-12) is a validated tool with 12 questions for the general assessment of the physical and mental health status of patients that is widely used in clinical studies. It is the shorter version of the SF-36 questionnaire. Two scores - one score for the physical component (PCS) and one score for the mental component (MCS) - represent the results. The SF-12 physical scale score represents general health perception, physical functioning, physical role functioning, and pain. The mental health score reflects emotional role functioning, mental well-being, negative affectivity, and social functioning. The questionnaire has already been used in various medical publications in different disciplines due to its wide range of applications. A low total value correlates with a poor quality of life, a higher one with a better one. The values determined are compared with the values of the normal population.

The Multidimensional Fatigue Inventory (MFI) is a 20-item scale designed to evaluate five dimensions of fatigue: general fatigue, physical fatigue, reduced motivation, reduced activity and mental fatigue. The German validated version is used. A scale from 1 to 7 is used to indicate how aptly certain statements regarding fatigue represent the participants' experiences. Higher total scores correspond with more acute levels of fatigue.

The Perceived Stress Scale (PSS-10) is a well-established self-report scale and an international standard instrument for measuring perceived stress. The ten questions ask about feelings and thoughts during the last month. In each case, respondents are asked how often they felt a certain way on a five-point scale from 'never' to 'very often'. The PSS score is obtained by summing across all items after responses to the four positively stated items have been reversed. Higher scores indicate higher levels of perceived stress.

Anxiety and depression are measured using the Hospital Anxiety and Depression Scale (HADS). The HADS was developed specifically for physically ill patients in clinical settings. The questionnaire contains 14 items: 7 on the anxiety and 7 on the depression scales. The sum values of the HADS-A (anxiety) and HADS-D (depression) scales lie in the 0-21 range, with higher values indicating a stronger manifestation of anxiety/depressiveness. The German validated version is used.

A validated questionnaire for the systematic assessment of food-related quality of life (FR-QoL) in IBD patients is used to assess psychosocial factors in connection with eating and drinking, such as enjoying food, managing restrictions, and maintaining social relationships. The FR-QoL-29, which contains 29 items, each scored on a 5-point Likert scale (1 = strongly agree; 2 = agree; 3 = neither agree nor disagree; 4 = disagree; 5 = strongly disagree), with 4 questions reversed for scoring. Scores are summed, with a total possible score ranging from 29 to 145, where higher scores reflect a greater FR-QoL.

A food frequency questionnaire (FFQ) is used to determine the frequency of consumption and usual portion sizes of a total of 53 food groups consumed in the last four weeks. The dietary questionnaire was developed and validated for the use in the German Health Examination Survey for Adults 2008-2011 (DEGS). In this study it is used to assess whether the participants' dietary habits change throughout the study and whether they apply the diet taught during nutritional therapy at the inpatient stay at the clinic for internal and integrative medicine in Bamberg.

Over the course of the study, the participants keep a diary in which they document their daily blueberry intake and symptoms to enable the evaluation of their compliance and their tolerance of the blueberry powder.

At week 0, participants undergo a colonoscopy with confocal laser endomicroscopy (CLE) when clinically indicated as part of their inpatient care. Thereby, the inflammatory status and the intestinal barrier is routinely analyzed. Participants return for a voluntary colonoscopy or sigmoidoscopy at week 12 and week 24. Confocal laser endomicroscopy (CLE, Cellvizio System from Mauna Kea Technology) is the first technology that enables live characterization of the intestinal mucosa and barrier integrity at the cellular level during endoscopy at up to 1000x magnification, allowing local intestinal barrier disorders to be identified and targeted biopsies to be taken. This combined examination of endoscopy and CLE thus enables a comprehensive assessment of the intestinal mucosa on a macroscopic, microscopic and functional level in real time.

Intestinal biopsies, which are routinely taken during colonoscopy/sigmoidoscopy, are processed for histopathological analysis of the mucosal and epithelial structure as well as of the immune cell compartment (H&E staining).

Intestinal biopsies, which are routinely taken during ileocolonoscopy, are stained using immunohistochemistry and examined for the expression of specific marker proteins. For example, the intestinal barrier will be examined by immunohistochemical analysis of the tight junction marker proteins occludin and claudin-2 or the migration of specific immune cells such as T-lymphocytes using CD3 staining.

Intestinal biopsies taken in addition to those routinely taken during ileocolonoscopy are used for transcriptional analysis by q-PCR to study the gene expression of particular immune cell or inflammatory marker proteins as well as tight junction proteins.

To evaluate the systemic inflammatory status, the level of various cytokines such as IL-1β, IL-6, IL-8, IL-10, TNF, IFN-γ, IL-17or IL-4 is analyzed in the serum.

A complete blood count including iron status and liver markers is made. It provides information about the number and type of immune cells. In combination with the general inflammatory markers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), the complete blood count allows conclusions about the presence and extent of systemic inflammation as well as the disease activity. Checking the iron status and liver markers can provide indications of IBD-associated complications such as anemia and liver dysfunction.

The concentration of the inflammation marker CRP is measured in the blood.

Determination of the ESR of the blood.

Besides Calprotectin, also the concentrations of other inflammatory markers such as Lactoferrin and PMN-Elastase are analyzed in the stool to evaluate the intestinal inflammation status quantitatively.

The concentrations of fecal biomarkers such as Zonulin or α-1-Antitrypsin are determined to quantitatively evaluate the integrity of the intestinal barrier.

The I-FABP concentration is measured in serum samples to evaluate the intestinal permeability. I-FABP is a protein exclusively found in intestinal epithelial cells. If the intestinal epithelium is damaged, I-FABP is released into the circulation and can be measured in the serum. Therefore, I-FABP serum levels are a valid biomarker for intestinal permeability in coeliac disease, wheat sensitivity and also in inflammatory bowel disease.

Fecal concentrations of the antimicrobial peptide β-Defensin are determined in the stool.

The fecal microbiome is analyzed in stool samples in order to determine the influence and the prebiotic properties of the blueberry-rich diet on the intestinal microbiome.

Microbial metabolites such as short chain fatty acids (SCFAs) are analyzed in stool samples in order to determine the influence and the prebiotic properties of the blueberry-rich diet on the intestinal microbiome. Prebiotics are nutritional components that promote the growth and activity of beneficial bacterial species. Prebiotics serve as a nutritional basis for these bacteria and promote, for example, their production of SCFAs that act as essential energy substrates for enterocytes and immune cells. These metabolites have been shown to influence immune cell maturation, immune homeostasis, host energy metabolism and the maintenance of mucosal integrity. Therefore, the combined evaluation of microbiome and microbial metabolites in the stool can contribute to a better understanding of the interplay of these factors in the development and treatment of IBD.

Metabolite profiling is done from urine samples. This can also provide valuable insights into the (dys)regulation of gut microbial metabolism and host-microbe co-metabolism in the context of IBD.

8-hydroxy-2-deoxyguanosine (8-OHdG) is analyzed in urine samples as a marker for oxidative stress in order to evaluate the antioxidant potential of the blueberry-rich diet. Oxidative stress plays an important role in a variety of chronic inflammatory diseases, including IBD. Oxidative stress describes a disturbance in the balance between the production and accumulation of reactive oxygen species (ROS). ROS are scavenged by the antioxidant system but can oxidize proteins, lipids and DNA in excessive concentrations. Resulting DNA damage is normally repaired and the oxidation products are excreted in the urine. 8-OHdG, a product of DNA guanine residue oxidation by ROS is an established biomarker for oxidative damage to DNA. Blueberries are known for their antioxidant potential. To evaluate the influence of a blueberry-rich diet on oxidative stress and antioxidant potential, 8-OHdG is analyzed in urine samples.

In addition to the evaluation of oxidative stress in the urine, the systemic antioxidant capacity of the blood is analyzed in serum samples as a reduced total antioxidant capacity can reflect the clinical disease activity.

The thiol status records the protective, free thiol groups that intercept extracellular radicals and bind toxic metals and pollutants. The thiol status is therefore a parameter of the extracellular protective system. Reduced thiol levels promote oxidative stress and serve as a marker for chronic inflammatory processes.

The peroxidation of lipids is evaluated in the serum. The determination of lipid peroxides can indicate an imbalance in antioxidant homeostasis.

Lipid peroxides are formed by the reaction of free radicals (ROS) with lipid structures, whereby unsaturated fatty acids contained in lipid membranes or lipid vesicles are oxidized. An excess of lipid peroxides is associated with chronic inflammatory processes.

In case an esophagogastroduodenoscopy is performed as part of the routine inpatient care, a sample of bile fluid is collected by simple aspiration from the duodenum in order to assess the secretion and composition of bile acids and their metabolites. Bile acids and their metabolites can have a significant impact on gut health in IBD patients. They have the capacity to modulate inflammation, alter the microbiome and affect the intestinal barrier integrity by regulating the expression of tight junction proteins that control the permeability of the gut wall.

Data collected during anamnesis in the course of the routine in-patient stay such as the course of disease or working ability are documented to enable an evaluation of the participants' medical condition and health status.

Concomitant medication and especially CED-related therapy of the study participants is documented throughout the study.

Information on concomitant diseases and the medical history of the study participants is routinely collected and recorded in the course of the in-patient stay as well as in the course of the study to evaluate the participants' medical condition and health status.

Social demographic aspects are collected in order to describe the patient collective of the study participants.