Fermented Foods Diet Drops 19 Inflammatory Markers In 10-Week Trial
A trial published in Cell found that adding fermented foods to the diet dropped 19 of 93 circulating inflammatory markers over 10 weeks, while a matched high-fiber diet produced 0 change in those same markers.
Thirty-six generally healthy adults, average age 51, 73% women, completed a 17-week diet study published in Cell in August 2021, with 18 people in each of two groups. One group added fiber-rich foods like legumes, whole grains and vegetables, raising daily fiber intake from 21.5 grams to 45.1 grams. The other group added fermented foods such as yogurt, kefir, kimchi and kombucha, raising intake from 0.4 servings a day to 6.3 servings a day. Researchers tracked participants for three weeks before the diet began, then four weeks of ramping up intake, six weeks of maintaining the higher intake, and four more weeks where participants chose their own level.
Blood and stool samples were analyzed for 93 different inflammation-related proteins circulating in the blood, along with gut microbe patterns and immune cell activity. The study's primary measure, called the Cytokine Response Score, a lab test of how reactive immune cells are, did not change in either group. But secondary results split sharply: the fermented-food group showed a drop in 19 of the 93 inflammatory markers over 10 weeks, including IL-6, IL-10 and IL-12b, three proteins linked to chronic, low-grade inflammation. The high-fiber group showed 0 of these 19 markers move. The fermented-food group's community of gut microbes, the mix of species living in the intestine, also grew steadily more diverse through the 10-week maintenance period, while the fiber group's did not.
Inflammatory Markers Dropped: 19 vs 0 Over 10 Weeks
Fermented foods appear to work differently than fiber does. Fiber feeds existing gut microbes, and in this trial it boosted 11 microbial enzymes involved in breaking down plant carbohydrates without changing the overall diversity of species present. Fermented foods, by contrast, seemed to reshape the community itself: new bacterial strains not found in the foods themselves became detectable in participants' guts, suggesting fermented foods create conditions that let previously rare microbes expand. That broader mix of gut microbes correlated with the drop in circulating inflammatory proteins and with reduced activation signals in four types of immune cells, addressing a basic question in gut health: can a food-based change reliably calm systemic inflammation, not just shift which bacteria happen to be present.
This was a small trial, 18 people in each group, with no placebo-style comparison diet, only the two active groups compared to each other and to their own starting point. Everyone studied was already healthy, so it is unclear whether the same drop in inflammatory markers would appear in someone managing an inflammatory condition. The intervention ran 10 weeks; whether the drop in markers or the rise in microbial diversity would continue, plateau or reverse over months was not tracked. The primary outcome showed no change, and the inflammation drop is a secondary finding, not a claim that any diagnosed disease was treated or prevented.
Data Panel
- Who
- 36 generally healthy adults (18 in each group), average age 51, 73% women, average BMI 25
- Design
- Randomized, prospective 17-week study (Cell, 2021), tracked participants for three weeks before the diet began, then a 4-week ramp-up, 6-week maintenance phase and 4-week choice period; no placebo diet, groups compared to each other and to their own baseline
- Dose
- High-fiber group: fiber intake rose from 21.5 grams a day to 45.1 grams a day. High-fermented-food group: intake rose from 0.4 servings a day to 6.3 servings a day
- Primary result
- Primary outcome, the Cytokine Response Score, a lab measure of immune reactivity, did not change in either group. The fermented-food group showed cohort-wide decreases in 19 of 93 circulating inflammatory markers over 10 weeks, including IL-6, IL-10 and IL-12b; the fiber group showed 0 of these 19 markers change.
- Secondary
- Fermented-food group: gut microbe diversity rose steadily through 10 weeks; 14 of 60 immune cell-signaling responses decreased. Fiber group: no cohort-wide change in microbe diversity; 11 microbial enzymes for breaking down plant carbohydrates increased.
- Funding / conflicts
- Not reported
Dr. Axe's Take
What stands out to me is that the fermented-food group changed almost nothing else and still saw 19 inflammatory markers drop over 10 weeks, while the high-fiber group, despite raising intake to 45 grams a day, saw none of those same markers move. I would not read this as fiber failing, six weeks of higher intake may simply be too short for fiber to reshape microbial diversity. This week, I would add one fermented food daily, plain yogurt, kefir or sauerkraut, while keeping fiber intake steady rather than choosing one over the other.
— Dr. Axe