Fermented foods and visceral fat: what the research actually says

The short version: there's real, encouraging evidence that fermented foods change the gut and calm inflammation, and that some specific probiotic strains modestly reduce visceral fat. There isn't yet a large, long trial proving that a fermented-food-with-every-meal diet melts visceral fat on its own. Here's what we know.

Fermented foods reshape the gut and lower inflammation

The best-known study comes from Stanford. In a 2021 trial published in the journal Cell, Wastyk and colleagues assigned 36 healthy adults to either a high-fermented-food diet or a high-fiber diet for 10 weeks. The fermented-food group ate yogurt, kefir, kimchi, sauerkraut, kombucha and similar foods, working up to about six servings a day.

The fermented-food group's gut bacteria became more diverse, and a broad panel of inflammatory markers went down. The high-fiber group did not see the same diversity gain over that period. Chronic inflammation and visceral fat feed each other, so this is a meaningful finding, though the study didn't measure visceral fat directly.

Some probiotic strains reduce visceral fat on scans

The most-cited visceral fat work tested one strain, Lactobacillus gasseri SBT2055, delivered in fermented milk. In a 12-week randomized, placebo-controlled trial in Japan (Kadooka and colleagues, 2010), adults with extra belly fat who drank the probiotic milk saw their visceral fat area on CT scans fall by roughly 4 to 5 percent, while the placebo group did not. A follow-up trial in 2013 found a similar effect at a lower dose.

Two details matter. The effect was modest, and in the first trial it faded within weeks after people stopped drinking the milk. That fits the "with every meal" idea: benefits seem to depend on keeping the bacteria coming.

Other trials with different Lactobacillus and Bifidobacterium strains have found small reductions in waist size or visceral fat, and several have found nothing. Reviews that pool these studies generally report small average effects on body fat, with a lot of variation between strains.

Where the evidence is thin

• Strains differ. A result for one strain doesn't transfer to "probiotics" in general, or to a jar of sauerkraut.
• Trials are short and small. Most run 8 to 12 weeks with fewer than 100 people.
• Industry funding is common. Many probiotic trials are paid for by the companies that sell the strain.
• Diet changes travel together. People who add fermented foods often cut sugar and processed food too, which makes it hard to credit the ferments alone.

What this means at the table

Eating traditional fermented foods is low-risk for most people, makes gut bacteria more diverse and appears to lower inflammation. Combined with cutting added sugar and refined starch, which has the strongest evidence for shrinking visceral fat, it's a reasonable daily habit. Just treat the probiotic piece as promising rather than proven, and track your own results with a waist measurement or scan.

We update this article as new studies come in. Follow every new paper on the research log.

Studies cited

• Wastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021. Find on PubMed
• Kadooka Y, et al. Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial. European Journal of Clinical Nutrition, 2010. Find on PubMed
• Kadooka Y, et al. Effect of Lactobacillus gasseri SBT2055 in fermented milk on abdominal adiposity in adults in a randomised controlled trial. British Journal of Nutrition, 2013. Find on PubMed