The Effect of Low or High Dietary Fiber Diet on Volatile Organic Compounds in Exhaled Breath of Healthy Individuals

The aim of this crossover intervention study is to evaluate the volatile organic compounds (VOCs) present in participants at baseline and how these levels change after consuming either a low- or high-dietary fiber diet for three days. This study will involve adults, 18-65 years old, without any gastrointestinal diseases. The primary objectives are to characterize baseline VOC profiles, assess changes in these profiles after a short-term dietary fiber intervention, determine if specific VOC patterns correlate with dietary fiber intake, and identify the time points at which VOC levels peak. This information will help establish the optimal timing for breath sampling and potentially provide insight into how VOC patterns relate to dietary fiber consumption and degradation. The expected outcome is that a high-dietary fiber diet will produce a VOC profile enriched in metabolites associated with fiber fermentation compared to a low-dietary fiber diet, and that these VOCs will be consistent with those identified in vitro during fecal fermentation. Each participant will serve as an internal control, enabling within-subject comparisons of VOC levels at baseline and following the dietary fiber intervention. Participants will receive a whole-food product that is rich in dietary fiber and will consume either a low-fiber diet (10 g/day) or a high-fiber diet (40 g/day) for three days. On the first day of each intervention, participants will also ingest a pH capsule to monitor gastrointestinal pH continuously throughout the three days. After a three-week washout period, participants will cross over to the other intervention arm and undergo another round of gastrointestinal pH monitoring. In addition to the dietary intervention, participants will complete food and health questionnaires to assess habitual fiber intake and dietary habits. Fecal samples will be collected for in vitro fermentation to functionally profile the gut microbiota by assessing fecal VOCs, short-chain fatty acids (SCFA), and the microbial enzymatic activity and its pH-dependent modulation.

NCT Number	NCT07594600
Lead Sponsor	Örebro University, Sweden Collaborators: University of Helsinki, European Innovation Council
Conditions	Healthy Adults, Dietary Fiber Fermentation
Enrollment	20 participants
Start Date	2026-05-25
Primary Completion	2026-11 (estimated)
Study Completion	2027-03 (estimated)
Updated on ClinicalTrials.gov	2026-06-04