Dietary fibre consumption at breakfast stimulates the production of exhaled bacteria-derived metabolites reflecting profound changes in the metabolic activity of the gut microbiota, and new potential biomarkers of dietary fibre intake were identified that are not directly linked to dietary fibre fermentation.
Key Findings
Results
A high-fibre breakfast (16.1 g) produced a measurable shift in exhaled breath composition beginning 5 hours after ingestion compared to a low-fibre breakfast (2.6 g).
14 healthy volunteers (7 women/7 men, 21 ± 2 years old) participated in a crossover design with two test days one month apart
Breath samples were analysed throughout each test day using selected-ion flow-tube mass spectrometry (SIFT-MS)
The shift in breath composition was detectable starting from 5 hours after high-fibre breakfast ingestion
A sparse partial least squares-discriminant analysis (sPLS-DA) identified 30 signals best discriminating between test days, corresponding to 173 candidate breath compounds
Results
Ninety breath compounds were identified as potential metabolites of gut microbes, with 81 showing increased concentrations after the high-fibre breakfast.
Of 173 candidate breath compounds identified by sPLS-DA, 90 were classified as potential gut microbial metabolites
81 of these 90 compounds showed increased concentrations following the high-fibre (16.1 g) compared to the low-fibre (2.6 g) breakfast
Untargeted breath volatilome analysis was used to detect these compounds
The analysis was conducted in healthy volunteers with stable gut microbiota composition across the one-month interval between test days
Results
Acrylic acid in exhaled breath was positively correlated with Faecalibacterium/Ruminococcaceae/Bacillota and negatively correlated with Bifidobacterium/Bifidobacteriaceae/Actinomycetota.
Acrylic acid was among the compounds increased after the high-fibre breakfast
Gut microbiota composition was assessed by Illumina sequencing of the V5-V6 region of the 16S rRNA gene from stool samples collected before each test day
The dual correlation pattern of acrylic acid with both Faecalibacterium (positive) and Bifidobacterium (negative) suggests differential microbial production pathways
Faecalibacterium is described as a bacterium known to play a role in gut barrier, immunity and host metabolism
Results
Limonene, ethylbenzene/xylene, p-cymene, and methionol in exhaled breath were positively correlated with the genus Faecalibacterium following high-fibre breakfast.
These compounds are identified as new potential biomarkers of dietary fibre intake that are not directly linked to dietary fibre fermentation
All four compounds showed increased concentrations after the high-fibre (16.1 g) breakfast
Faecalibacterium is a genus known to play roles in gut barrier function, immunity, and host metabolism
These correlations were established using microbiota composition data from stool samples collected before each test day
Results
Cyclooctane/ethylcyclohexane and methanol in exhaled breath showed positive correlations with the phylum Bacillota.
These compounds were among the 81 breath metabolites showing increased concentrations after the high-fibre breakfast
Bacillota (formerly Firmicutes) is a major gut bacterial phylum
Correlations were established between breath volatile concentrations and microbiota composition determined by 16S rRNA gene sequencing
These represent novel associations not previously reported in dietary fibre research
Results
Dimethyl disulfide in exhaled breath was strongly negatively correlated with the genus Bacteroides and its family Bacteroidaceae.
Dimethyl disulfide is a sulfur-containing volatile compound detectable in exhaled breath
The negative correlation with Bacteroides suggests this taxon may consume or inhibit production of this compound
This association was identified through correlation analysis between SIFT-MS breath data and 16S rRNA sequencing data
Bacteroides and Bacteroidaceae are major components of the human gut microbiota
Results
The gut microbiota composition of volunteers remained stable over the one-month interval between the two test days.
Stool samples were collected before each test day for microbiota analysis
Illumina sequencing of the V5-V6 region of the 16S rRNA gene was used to assess microbiota composition
Stability of microbiota confirmed that differences in breath volatile profiles between test days were attributable to the dietary intervention rather than changes in baseline microbial community structure
14 healthy volunteers participated in the crossover design with a one-month washout interval
Methods
Exhaled breath analysis using SIFT-MS provides a non-invasive method to study dietary fibre-microbiome interactions in humans.
Selected-ion flow-tube mass spectrometry (SIFT-MS) was used for untargeted breath volatilome analysis throughout each test day
Breath sampling captured real-time changes in microbial metabolic activity following dietary fibre consumption
The approach identified metabolites that would not be detected by conventional targeted stool or blood metabolomics
The study proposes breath volatilome analysis as a new non-invasive method to study dietary fibre-microbiome interactions in humans
What This Means
This research suggests that what you eat for breakfast — specifically how much dietary fibre it contains — can change the chemical composition of your breath within hours, and these breath chemicals reflect the activity of bacteria living in your gut. In a small study of 14 healthy young adults, researchers gave participants either a low-fibre breakfast (2.6 g of fibre) or a high-fibre breakfast (16.1 g of fibre) on two separate occasions one month apart. By continuously analyzing exhaled breath using a sensitive mass spectrometry technique, the researchers found that about 5 hours after eating the high-fibre meal, the breath contained measurably higher levels of dozens of chemical compounds linked to gut bacterial activity.
Among the most interesting findings, the study identified several breath chemicals — including acrylic acid, limonene, and methionol — whose levels correlated with specific types of gut bacteria known to be important for gut health and immune function, particularly a bacterium called Faecalibacterium. Notably, some of these breath biomarkers do not appear to be direct products of fibre fermentation, suggesting they arise through more indirect microbial metabolic pathways that are not yet fully understood. The gut bacteria themselves did not change between the two test days, confirming that the breath differences were caused by the dietary fibre rather than shifts in which bacteria were present.
This research suggests that analysing exhaled breath could become a practical, non-invasive tool for studying how diet affects gut bacteria in humans, potentially avoiding the need for stool or blood samples. The identification of new breath-based biomarkers linked to high-fibre diets may eventually help researchers and clinicians monitor whether dietary interventions are effectively stimulating beneficial gut microbial activity, although much larger studies would be needed to confirm and extend these findings.
Autuori M, Neyrinck A, Lengelé L, Olivera E, Rombaux M, Rodriguez J, et al.. (2026). Breath volatilome analysis reveals new gut microbiome-related metabolites that discriminate high versus low dietary fibre intake.. Clinical nutrition (Edinburgh, Scotland). https://doi.org/10.1016/j.clnu.2026.106662