Diet shapes the gut microbiome, and the microbiome shapes immune function. That chain is widely accepted and rarely tested head to head in people. So healthy adults were randomized for 17 weeks to a high-fiber diet or a high-fermented-food diet, 18 per arm, with deep immune and microbiome profiling throughout. The prespecified primary outcome was a . Which diet moved what?
The two diets did different things, and the primary outcome moved for neither. Fiber raised the microbiome’s glycan-degrading enzymes while community diversity stayed flat, and the fiber eaters split into three according to their starting diversity. The fermented-food diet steadily increased and decreased inflammatory markers. The cytokine response score, the outcome named in advance, was unchanged.
Diet modulates the gut microbiome, and the microbiome can in turn affect the immune system. Both halves of that are well supported. What had rarely been done is to take two dietary strategies aimed at the microbiome and run them against each other in healthy people, with enough measurement to see what each one actually does.
The design was a seventeen-week randomized prospective study with 18 participants per arm, one on plant-based fiber and one on fermented foods. Omics measurements of the microbiome ran alongside extensive immune profiling of the host.
The high-fiber diet increased microbiome-encoded glycan-degrading , while microbial community diversity stayed stable. The cytokine response score, the primary outcome, was unchanged. But three distinct immunological trajectories appeared among the fiber consumers, and which one a person followed corresponded to their baseline microbiota diversity.
The fermented-food arm behaved differently. It steadily increased microbiota diversity and decreased inflammatory markers. The authors suggest fermented foods may be valuable against the low diversity and raised inflammation common in industrialized societies, and they frame the whole exercise as a case for coupling diet trials to deep profiling. Read the scale before the conclusion: eighteen people an arm, a primary outcome that did not move, and inflammatory markers rather than illness.
wat. Fermented food raised gut diversity and lowered inflammatory markers; fiber changed the gut’s enzymes and split the eaters into three different responses.
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Fiber and fermented food get recommended together as though they do the same job. Here only one of them raised diversity and lowered inflammation, and the fiber response depended on the gut somebody already had.
How do we know?
Wastyk and colleagues ran a 17-week randomized prospective study with 18 healthy adults per arm, combining a high-fiber or high-fermented-food diet with omics profiling of the microbiome and extensive immune profiling.
What is still unknown
Eighteen people per arm, and the primary outcome was unchanged, so the diversity and inflammation results are secondary findings in a small study. Inflammatory markers are surrogates, not disease.
Learn something?
Where to next
How do bacteria in a mouse’s gut change the way it behaves?microbiomeWhat happens to a mouse raised with no gut bacteria at all?microbiome
How many bacteria are there really in your body per human cell?microbiome