In a 10-week randomised trial of 36 healthy adults, eating more fermented foods steadily increased the diversity of gut microbes and lowered 19 inflammatory proteins in the blood. Doubling fibre intake also changed what the gut microbes were equipped to do and the capacity to break down plant carbohydrates rose across the group.
What was interesting, was that while the foods acted on the gut in different ways, the combination of the two was what they concluded was worth studying.Β
The study
The Fermented and Fibre-rich Food (FeFiFo) study was run at the Stanford School of Medicine and published in Cell in 2021. Participants were randomly assigned to one of two diets and tracked for 17 weeks: high-fibre and high-fermented food.Β
What fermented foods did
Fermented foods broadened the gut community and calmed several measures of immune activity, consistently across the group. This held whether participants ate mostly fermented dairy or mostly fermented vegetables.
- Diversity rose
- New microbes mostly did not come from the food
-
Yoghurt and vegetable brine drinks showed the strongest link with rising diversity, though they were also the most commonly eaten.
- 19 of 93 inflammatory proteins fell
-
Immune cells were less activated. Across four major immune cell types, 14 of 60 signalling measures decreased and only one increased.
-
Bloating rose briefly during the ramp-up, then settled by the high-intake phase
What diverse fibre did
Participants were coached to draw fibre from a variety of sources, and their ratio of insoluble to soluble fibre rose over the study.
- The microbial population appears to have grown
-
Fibre-processing machinery increased. Eleven carbohydrate-active enzymes became more abundant and none declined
-
Some fibre passed through undigested. The more fibre a person ate, the more carbohydrate appeared in their stool
-
Immune responses depended on the starting microbiome. Participants fell into three groups. Two showed reduced immune activation; one showed increased activation. Those with more diverse microbiomes at the start tended towards the lower-inflammation responses.
-
Diversity held steady. The number and spread of microbial species did not change.
-
Stools became softer, moving from an average of 3.3 to 4.1 on the Bristol Stool Scale.
Fibre eaters also consumed more iron, magnesium, potassium, vitamin C and calcium, and less animal protein and sodium.
Side by side
|
Measure
|
High-fibre diet
|
High-fermented-food diet
|
|
Microbial diversity
|
No change
|
Increased steadily
|
|
Fibre-degrading enzymes
|
11 increased
|
8 decreased
|
|
Inflammatory proteins in blood
|
No consistent change
|
19 decreased, incl. IL-6
|
|
Immune cell activation
|
Varied by person
|
Decreased across the group
|
|
Undigested carbohydrate in stool
|
Rose with intake
|
Not reported
|
|
Gut symptoms
|
Softer stools
|
Temporary bloating
|
Limitations
The authors note the study was small (18 people per group) and had no control group, so each diet was compared with the other and with participants' own baseline. The intervention lasted 10 weeks, so how durable the changes are is unknown. The study shows associations between diet, microbes and immune markers; it does not establish cause.
What this means for everyday eating
The trial suggests fibre and fermented foods do different jobs. Varied fibre fed and retooled the microbes already present; fermented foods were associated with a broader community and lower inflammatory markers.Β
Read the full original study
Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153.e14. doi.org/10.1016/j.cell.2021.06.019 Β· PubMed
Fibre and fermented foods: what a Stanford trial discovered about the gut
In a 10-week randomised trial of 36 healthy adults, eating more fermented foods steadily increased the diversity of gut microbes and lowered 19 inflammatory proteins in the blood. Doubling fibre intake also changed what the gut microbes were equipped to do and the capacity to break down plant carbohydrates rose across the group.
What was interesting, was that while the foods acted on the gut in different ways, the combination of the two was what they concluded was worth studying.Β
The study
The Fermented and Fibre-rich Food (FeFiFo) study was run at the Stanford School of Medicine and published in Cell in 2021. Participants were randomly assigned to one of two diets and tracked for 17 weeks: high-fibre and high-fermented food.Β
What fermented foods did
Fermented foods broadened the gut community and calmed several measures of immune activity, consistently across the group. This held whether participants ate mostly fermented dairy or mostly fermented vegetables.
What diverse fibre did
Participants were coached to draw fibre from a variety of sources, and their ratio of insoluble to soluble fibre rose over the study.
Fibre eaters also consumed more iron, magnesium, potassium, vitamin C and calcium, and less animal protein and sodium.
Side by side
Measure
High-fibre diet
High-fermented-food diet
Microbial diversity
No change
Increased steadily
Fibre-degrading enzymes
11 increased
8 decreased
Inflammatory proteins in blood
No consistent change
19 decreased, incl. IL-6
Immune cell activation
Varied by person
Decreased across the group
Undigested carbohydrate in stool
Rose with intake
Not reported
Gut symptoms
Softer stools
Temporary bloating
Limitations
The authors note the study was small (18 people per group) and had no control group, so each diet was compared with the other and with participants' own baseline. The intervention lasted 10 weeks, so how durable the changes are is unknown. The study shows associations between diet, microbes and immune markers; it does not establish cause.
What this means for everyday eating
The trial suggests fibre and fermented foods do different jobs. Varied fibre fed and retooled the microbes already present; fermented foods were associated with a broader community and lower inflammatory markers.Β
Read the full original study
Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153.e14. doi.org/10.1016/j.cell.2021.06.019 Β· PubMed