Effects of Changing Intestinal Transit Time on Gut Microbial Composition and Metabolism

Effects of Changing Intestinal Transit Time on Gut Microbial Composition and Metabolism During a Dietary Intervention with Low and High Fiber.

The aim of this study is to investigate how a short versus a long transit time impacts the gut microbiome's response to a high-fiber and a low-fiber diet, respectively. Such insights could help us understand personal responses to diets and be a first step towards personalized dietary recommendations targeting the gut microbiome.

The study consists of two parallel arms of whole-meal diets, a low-fiber diet, and a high-fiber diet, respectively. Each arm is designed as a cross-over where participants, in random order, are administered a laxative (Movicol) along with the provided diet to shorten their intestinal transit time or simply consume the provided whole-meal diet (control).

The two intervention periods both involve the following:

• One week of run-in where participants consume the provided whole-meal diet.
• One week where participants either consume Movicol with the provided whole-meal diet or simply continue consuming the provided whole-meal diet (control).

Both arms begin with a screening visit and one week where participants consume and record their habitual diets. Subsequently, the first intervention period follows with one visit before and after each of the two weeks (visit 1-3) followed by the second intervention period with one visit before and after each of the two weeks (visit 4-6). The two cross-over periods are split by a washout of at least two weeks.

The study thus runs for approximately 7-8 weeks depending on the length of the washout and consists of seven visits (one screening visit and six regular visits) in total.

Inclusion Criteria:

• 18.5-30.0 kg/m2 BMI
• Self-reported ≤3.5 spontaneous bowel movements per week
• Willing to collect urine and stool samples at home and able to temporarily store them in their own freezer in a provided container.
• Willing to eat the foods provided.
• Owns a smartphone (iOS 11.0 and later or Android 5.0 and up) with access to the internet.

Exclusion Criteria:

• Pregnant or lactating women.
• Diagnosis of irritable bowel syndrome (IBS), small intestinal bacterial overgrowth (SIBO), inflammatory bowel diseases (IBD), Gastrointestinal obstruction, or Ischemic colitis
• Diagnosed constipation according to the ROME IV criteria
• Intake of antibiotics ˂ 1month, or any medication that can affect the outcomes of the study
• Regular use of diarrhea inhibitors or laxatives
• Dysphagia
• Any chronic disease that can affect the outcomes of the study or pose a risk when consuming Movicol
• Intake of medications potentially altering gastric pH (proton pump inhibitors, histamine receptor antagonists, antacids)
• Intake of medications potentially altering the gastrointestinal motility (prokinetics, antiemetic agents, anti-cholinergic agents, narcotic analgetics, nonsteroidal anti-inflammatory drugs, and peroral glucocorticoids)
• Concurrent participation in another trial
• Any condition that makes the project responsible researcher to doubt the feasibility of the volunteer´s participation