Fermented foods failed to move two of three inflammation markers

Fermented foods carry a growing reputation for calming chronic inflammation, the low-grade immune activity linked to many long-term health problems. Individual trials testing that idea have returned inconsistent results, with some showing changes in inflammatory blood markers and others showing none. C-reactive protein, interleukin-6 and tumour necrosis factor alpha are the markers most commonly measured in this research. This analysis pooled the randomised trials in generally healthy adults to see whether the reputation is earned.

The researchers searched PubMed and Scopus up to June 2019, initially identifying 3293 documents. Twenty-six publications met the inclusion criteria, covering 1461 adults from the general population. Each included trial compared a fermented food against a control product and measured at least one of the three inflammatory biomarkers. Results were pooled as mean differences using a random effects model, and subgroup analyses probed why the trials disagreed with each other.

Pooled across trials, fermented food intake was linked to a reduction in TNF-α, with a weighted mean difference of 8.26. CRP did not change meaningfully, and neither did IL-6. In other words, two of the three markers examined showed no improvement at all. The disagreement between trials was extreme for all three markers, which makes even the TNF-α reduction difficult to interpret with confidence.

This tempers the popular narrative that fermented foods are broadly anti-inflammatory, at least as judged by standard blood markers in healthy adults. It does not rule out benefits: fermented foods vary enormously, and pooling different products, doses and durations may blur real effects of specific foods. The extreme disagreement between trials is itself informative, suggesting that if effects exist they are not consistent across products or populations. Which fermented foods help, in whom, and at what amount all remain open questions.

If you eat fermented foods hoping to lower inflammation, this is a reason to keep expectations modest: the best pooled evidence found no movement in CRP or IL-6. The drop in TNF-α is a genuine signal, but it comes from trials that disagreed with each other dramatically. Fermented foods may still earn their place in a diet for other reasons, but blanket anti-inflammatory claims are running ahead of the marker data shown here.