Why Calories Are Not the Same - a Gut Explanation?

The aim of this study is to understand how the gut microbiome influences how much dietary energy humans excrete via feces. This study is based on the hypothesis that levels of methane in exhaled breath represent two different gut microbiome community structures, and therefore influence fecal energy excretion differently. Moreover, this study is assessed in the context of two different diets, both isocaloric and equal in macronutrient composition, but differing in contents of fiber, resistant starch, and large particles; which are hypothesized to impact the gut microbiome differently.

The trial is a cross-over trial including two controlled isocaloric dietary interventions of three days duration. The two diets are isocaloric but with different contents of fiber, resistant starch, and food particle sizes. Each intervention is separated by a wash-out period of at least 10 days where participants adhere to their habitual diet. The trial includes a total of five visits (one screening visit and four regular visits).

Before the trial, participants undergo a screening period of 4 days. During the 4-day screening period, participants measure the levels of methane in their exhaled breath. Based on median breath methane levels, participants are allocated to one of the two arms: (HMP: high methane producers; LMP: low methane producers). Enrollment in the intervention trial will be conducted so there are similar numbers of participants in both arms.

At the beginning and at the end of each 3-day intervention period, participants consume a blue muffin, containing a royal blue dye that changes the stool color. The appearance of the color in stool following the first muffin will mark the beginning of the stool collection period, which will continue until the stool color change is no longer noticeable following consumption of the second muffin. Therefore, the duration of the stool collection period, which is estimated to be on average 3 days, will ultimately depend on the participants' passage time of food (i.e., intestinal transit time).

During the screening period, participants are asked to:

* measure their methane and hydrogen levels in exhaled breath using a portable device
* report defecation patterns (including stool frequency and Bristol Stool Scale)

Before each intervention period, participants are asked to:

* collect a fecal and urine sample
* register three days of habitual diet

At the visits before each intervention period, the following samples are collected:

* a blood sample
* methane and hydrogen measurements in exhaled breath
* anthropometrics
* data on physical activity

During the intervention periods, participants are asked to:

* exclusively eat all the foods provided
* collect all their stool samples, as specified above
* collect three morning urine samples (one daily for the following three days)
* measure their methane and hydrogen levels in their exhaled breath using a portable device
* report their defecation patterns and gastrointestinal symptoms

Eligibility Criteria:
Inclusion Criteria:

* 18-65 years old
* BMI:18.5-29.9 kg/m2
* Self-reported regular defecations defined as at least every second day
* 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 exclusively eat the food provided
* Owning a smartphone (iOS 11.0 and onwards, or Android 5.0 and onwards) with access to the internet
* Speak and understand Danish or English

Exclusion Criteria:

* Current pregnancy or lactation
* Following a specific dietary program or diet (e.g., vegetarian, vegan, gluten-free) or unable to consume the food provided
* Diagnosis of small intestinal bacterial overgrowth (SIBO), inflammatory bowel diseases (IBD), gastrointestinal obstruction, or ischemic colitis
* Diagnosed chronic constipation
* Regular use of diarrhea inhibitors or laxatives
* Any chronic disease that can affect the outcomes of the study
* Use of medications potentially altering gastric pH (proton pump inhibitors, histamine receptor antagonists, antacids)
* Use of medications potentially altering the gastro-intestinal motility (prokinetics, antiemetic agents, anticholinergic agents, narcotic analgesics, nonsteroidal anti-inflammatory drugs, peroral glucocorticoids, and GLP-1 related medications such as semaglutide and liraglutide)
* Use of antibiotics, or any medication that can affect any outcomes of the study, within the previous three months
* Concurrent participation in another trial
* Any condition that makes the project responsible and/or the clinical responsible doubt the feasibility of the volunteer's participation