Sourdough bread consumption caused a significant reduction in the diarrhoea sub-dimension score and increased several beneficial gut bacterial taxa compared to baker's yeast bread, though no statistically significant difference in overall gut symptom scores was demonstrated.
Key Findings
Results
Sourdough bread caused a significant reduction in the diarrhoea sub-dimension score compared to baker's yeast bread.
The diarrhoea sub-dimension score was significantly reduced with sourdough bread consumption (p = 0.016)
The overall GSRS-IBS score showed a borderline significant reduction with sourdough compared to baker's yeast bread (p = 0.051)
The study used a randomised, controlled, double-blind cross-over design with twenty healthy participants
Each bread type was consumed for one week before crossing over to the other
Results
Sourdough bread consumption significantly increased several Bifidobacterium species compared to baker's yeast bread.
Bifidobacterium adolescentis was significantly increased after sourdough bread intake (p = 0.042)
Bifidobacterium longum was significantly increased after sourdough bread intake (p = 0.010)
Bifidobacterium longum subspecies longum was significantly increased after sourdough bread intake (p = 0.021)
Faecal samples were collected before and after each intervention period for targeted gut microbial taxa analyses
Results
Sourdough bread consumption significantly increased Alistipes putredinis and Alistipes shahii compared to baker's yeast bread.
Alistipes putredinis was significantly increased after sourdough bread intake (p = 0.029)
Alistipes shahii was significantly increased after sourdough bread intake (p = 0.015)
There was a significant negative correlation between changes in diarrhoea score and changes in Alistipes shahii (r = -0.353, p = 0.025)
This correlation suggests that increases in Alistipes shahii were associated with reductions in diarrhoea symptoms
Results
The sourdough bread contained less fructose than the baker's yeast bread, despite both breads being made of whole grain wheat with similar macronutrient content.
Both breads were made of whole grain wheat
Both breads had similar macronutrient content
The sourdough bread contained less fructose than the baker's yeast bread
Reduced fructose content in sourdough may be a relevant factor in explaining differences in gut symptoms
Results
The overall GSRS-IBS score did not show a statistically significant difference between the two bread types.
The primary endpoint of overall GSRS-IBS score difference between sourdough and baker's yeast bread was not statistically significant
The p-value for the overall GSRS-IBS score was 0.051, described as 'borderline significant'
The authors described this as an 'exploratory cross-over study' that 'did not demonstrate a statistically significant difference in the overall GSRS-IBS score between the two breads'
The authors concluded that findings 'require further investigations'
Methods
The study design was a randomised, controlled, double-blind cross-over trial involving twenty healthy participants.
Twenty healthy participants were included in the study
Participants reported gut symptoms before and after each intervention
Blood samples were collected to analyse micronutrients and metabolic markers
Faecal samples were collected for targeted gut microbial taxa analyses
The double-blind design was employed to reduce bias in symptom reporting
What This Means
This research suggests that the type of bread people eat—sourdough versus regular baker's yeast bread—can affect gut symptoms and the types of bacteria living in the gut. In a small clinical trial with 20 healthy participants, each person ate one type of bread for a week, then switched to the other type. When people ate sourdough bread, they reported significantly less diarrhea compared to when they ate baker's yeast bread. Additionally, sourdough bread was associated with increases in several types of gut bacteria, including multiple Bifidobacterium species (which are generally considered beneficial) and Alistipes species. Notably, increases in one of these bacteria, Alistipes shahii, were associated with reductions in diarrhea symptoms.
One possible reason sourdough may affect the gut differently is that the fermentation process involved in making sourdough reduces the amount of fructose in the bread. Fructose is a type of sugar that some people have difficulty digesting, and lower amounts in food can sometimes mean fewer digestive symptoms. Both breads in this study were made from whole grain wheat and had similar amounts of protein, fat, and carbohydrates overall, making fructose content one of the notable differences between them.
This research suggests a potential link between sourdough bread consumption and improved gut comfort and gut microbiome composition compared to conventional baker's yeast bread. However, the study was small and exploratory, and the difference in overall gut symptom scores between the two breads did not reach the threshold for statistical significance. The authors emphasize that these findings need to be confirmed in larger studies before firm conclusions can be drawn.
Watters S, Henriksen C, Gjøvik M, Garnweidner-Holme L, Frederiksen M, Jonassen S, et al.. (2026). Sourdough Bread and Baker's Yeast Bread Affect Gut Symptoms and Targeted Gut Microbial Taxa Differently: A Randomised Controlled Trial.. Nutrients. https://doi.org/10.3390/nu18172854