Fermented vegetables and the gut microbiota in adults at cardiovascular risk
TL;DR
Eighty-seven adults at increased cardiovascular risk were randomized to usual diet or 100 g/day of naturally fermented kraut/kimchi at least five days/week for eight weeks. The intervention did not improve measured inflammatory biomarkers or bacterial alpha diversity. Gas or bloating was reported more often with fermented vegetables, providing an important counterweight to the positive exploratory Wastyk study.
Design
- Parallel randomized controlled trial; 87 adults aged 35–64 were randomized and 86 completed (mean age about 45 years, mean body-mass index 30 kg/m², approximately 80% women).
- Intervention: 100 g naturally fermented vegetables five days/week for eight weeks; average reported consumption was 630 g/week. Products were refrigerated local krauts and kimchis produced by natural fermentation and were not to be heated.
- Control: usual diet. Registry: NCT04887662.
- Outcomes included C-reactive protein, lipopolysaccharide-binding protein, trimethylamine N-oxide, angiopoietin-like protein 4, oxidized low-density-lipoprotein receptor 1, blood pressure, gastrointestinal symptoms, and stool 16S sequencing.
Key findings
- No significant between-group effect was found for any measured inflammatory/metabolic biomarker or for systolic or diastolic blood pressure.
- Shannon alpha diversity and observed amplicon-sequence variants did not change with the intervention. Baseline between-group beta-diversity differences persisted, but neither group changed significantly over time.
- Exploratory within-group LEfSe screening identified several taxon shifts, including enrichment of historical-genus Lactobacillus, while Faecalibacterium and Roseburia decreased in the intervention group. These findings were not a significant intervention effect on alpha or beta diversity, and the top phyla and 15 families did not differ significantly.
- Weekly symptom logs recorded bloating or gas more often in the fermented-vegetable group (19.3%) than in the usual-diet group (9.4%). The study foods added approximately 600 mg sodium/day; participants were counseled to reduce sodium elsewhere.
Limitations
The intervention was not blinded, the control lacked matched unfermented vegetables, participants also reduced calories and sodium within the intervention arm, and 16S sequencing had limited species/strain resolution. The two groups differed in beta diversity at baseline, and the within-group LEfSe screen does not establish that the fermented vegetables caused individual taxon changes. The study does not establish that higher doses would work; its null outcomes and tolerability findings argue against assuming a monotonic dose-benefit relationship. gap/contradictory-evidence