Skip to content
ZenBodyLove

Fermented foods and polyphenols

Randomised trials in healthy adults link eating fermented foods with modest improvements in bowel habits and gut comfort, and one small trial found a fermented-food diet raised gut microbiota diversity and lowered inflammatory markers; the certainty of this evidence is mostly low. Cohort studies associate fermented milks, cheese and chocolate with lower mortality. Among polyphenols, cocoa flavanols have moderate-certainty trial evidence for a small short-term fall in blood pressure, and cohort studies associate flavan-3-ol intake with better cardiometabolic outcomes. Concentrated green tea extract supplements are the main safety exception, with case reports of liver injury.

  • Longevity
  • Vegan

Evidence retrieved up to

What the research shows

In mainly healthy adults, flavanol-rich cocoa and chocolate products lowered blood pressure by a small amount, about 2 mmHg, in short-term trials.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsBenefit

Who this is about

mainly healthy adults

Practical note

Graded moderate, as the Cochrane authors did: 35 randomised trials with 1804 participants, downgraded for unexplained heterogeneity, with some sign of reporting bias. Trials supplied 30 to 1218 mg of flavanols a day (mean 670 mg) for 2 to 18 weeks. A 2019 meta-analysis of 156 trials of flavan-3-ols also found improved systolic blood pressure.

Vegan note

Cocoa is a plant food; dark chocolate made without milk is suitable for a vegan diet.

Safety note

Cocoa products were well tolerated in the trials, with gastrointestinal complaints and nausea in about 1 percent of participants.

Sources

In a small randomised study of healthy adults, a diet high in fermented foods increased gut microbiota diversity and lowered markers of inflammation; trials of plant-based fermented foods in adults with obesity or metabolic syndrome also reported increases in beneficial gut bacteria.

Very low certaintyThis is uncertain; treat it as a lead, not a finding.
No known concerns at usual amountsBenefit

Who this is about

healthy adults; adults with obesity or metabolic syndrome

Practical note

Graded very low: the main trial ran 17 weeks with 18 people per arm and reported surrogate markers, and only four trials in the botanical review measured gut bacteria, two with significant between-group differences.

Vegan note

The botanical fermented foods review covers plant-based fermented foods only.

Sources

In healthy adults, eating fermented foods was linked in randomised trials with more frequent bowel movements, softer stools, faster intestinal transit and fewer gastrointestinal symptoms such as bloating.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsBenefit

Who this is about

healthy adults

Practical note

Graded low, as the review authors also found: 19 randomised trials were pooled, but heterogeneity was high (I2 72 to 95 percent), the foods and outcomes varied widely, and the laboratory of one author declares dairy and probiotic industry funding.

Vegan note

The review covered both dairy and plant-based fermented foods; plant-based options include fermented vegetables such as sauerkraut and fermented cucumbers.

Safety note

Fermented vegetables such as sauerkraut and pickles can be high in salt; the review noted over 200 mg sodium per serving in fermented cabbage and cucumbers. Most trials gave no information on vulnerable groups or high intakes.

Sources

In prospective cohort studies of adults, higher intake of fermented milks such as yogurt, cheese and chocolate was associated with lower all-cause and cardiovascular mortality, while miso and bread showed no association.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsBenefit

Who this is about

adults in prospective cohort studies

Practical note

Graded low: observational evidence from 50 cohorts comparing highest with lowest intake, open to confounding by overall diet and lifestyle.

Vegan note

The foods with the clearest associations were dairy and chocolate; miso, a fermented soy food, showed no association.

Sources

In prospective cohort studies of adults, higher habitual intake of flavan-3-ol monomers was associated with lower risk of type 2 diabetes and stroke; as part of a healthy lifestyle, flavan-3-ol-rich foods may help reduce the risk of type 2 diabetes and stroke.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsBenefit

Who this is about

adults in prospective cohort studies

Practical note

Graded low: the review authors rated the cohort evidence moderate, but it is observational and the meta-analysis showed considerable heterogeneity. The associations were 10 and 18 percent lower risk of type 2 diabetes and stroke, comparing highest with lowest intakes.

Vegan note

Flavan-3-ols are plant compounds.

Sources

Concentrated green tea extract supplements have been linked in case reports to liver injury in adults, with large differences between individuals in susceptibility.

Low certaintyFurther research is likely to change this.
Take care: see the safety noteRisk

Who this is about

adults taking concentrated green tea extract supplements

Practical note

Graded low: the evidence is case reports with toxicology and bioavailability studies, reviewed by the USP. Case reports involved EGCG intakes from 140 mg to about 1000 mg a day, and repeated bolus doses taken while fasting raised catechin bioavailability.

Safety note

The USP added a label caution to its green tea extract monograph: take with food rather than on an empty stomach, do not use with a liver problem, and stop and consult a healthcare practitioner if signs of liver trouble such as dark urine or yellowing of the skin appear.

Sources