Humans have been fermenting food and drink for at least 13,000 years – and touting the health benefits for nearly as long. But despite our long history with them, we are only beginning to determine whether these foods are actually beneficial for our health.
Unlike our ancestors, however, we now know how fermentation works: microbes such as certain yeasts and bacteria break down sugars in grains, fruit, vegetables and dairy products in a way that prevents them from spoiling and produces unique flavours. But what does this mean for our health?
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Numerous studies have linked fermented foods – particularly dairy versions – to a . For instance, a involving more than 46,000 adults living in the US found that eating fermented foods was associated with lower blood pressure, body mass index and waist circumference.
But much of the research lumps all kinds of fermented foods together, and given the health halo around these products, we know that people who consume them probably tend to look after their health in other ways too. Both of these factors make it difficult to determine what is actually providing any observed benefits.
Benefits of yoghurt
That said, the case is strongest for yogurt. Many large studies have linked its consumption to , bone density and longevity and to a reduced risk of and . Yet determining cause and effect from these observational studies is tricky and some of the benefits may have nothing to do with fermentation. For example, yogurt is high in calcium, a nutrient helpful for stronger bones.
However, earlier this year, the US Food and Drug Administration announced that consuming at least three servings of yogurt per week may . This was based on multiple studies, including living in the US. It found that increasing yogurt consumption by more than half a serving per day was associated with an 11 per cent lower risk of developing type 2 diabetes over a four-year period.
People who consume fermented foods tend to look after their health in other ways too
Links between type 2 diabetes and unfermented dairy products are less robust, suggesting that these benefits are to do with the microbes found in yogurt, says at Tufts University in Massachusetts. We know that bacteria used to ferment yogurt release compounds called bioactive peptides and are believed to help lower blood pressure and regulate immune responses.
Live bacteria in yogurt can also affect the make-up of the gut microbiome, which plays a crucial role in regulating immune responses and metabolism. “The idea is that by providing bacteria through yogurt and introducing them into the gut, we are increasing the [amount of] beneficial bacteria,” says Meydani.
How other fermented foods might provide health benefits is less clear, says at the French National Institute for Agriculture, Food and Environment. We know, for instance, that dietary fibre feeds gut microbes and helps them flourish. Fermented and raw vegetables contain similar amounts of fibre, so it may be that, not the fermentation, that makes a difference.
To find out, Justin Sonnenburg at Stanford University in California and his colleagues put 36 adults on a diet rich in either . On average, those in the first group ate 45 grams of fibre per day without increasing their intake of fermented produce. Meanwhile, participants in the fermented food group ate an average of six servings of such fare daily without increasing their fibre intake.
After 10 weeks, those on the high-fibre diet saw no significant changes in the diversity of gut microbes or in blood levels of inflammatory markers, which can be used to track immune response, including chronic inflammation associated with conditions like heart disease, type 2 diabetes and cancer.
In people on the fermented food diet, however, researchers did see an increase in gut microbiome diversity. This was most strongly associated with consuming two things in particular: yogurt and vegetable brine, the liquid that fermented vegetables such as kimchi soak in. Compared with the start of the study, participants eating fermented foods also had lower levels of inflammatory markers. It appears fibre alone isn’t responsible for the benefits.
Gut microbiome boost
What’s more, researchers thought they would see the bacteria in fermented foods take up residence in participants’ guts. Few did. Instead, their presence seemed to somehow carve out a niche for new or previously undetected bacterial strains to flourish.
All of this suggests that fermented foods, especially yogurt, may give our health a boost. But it is still far from conclusive, says Meydani. More controlled trials are needed, as is a more detailed understanding of specific bacterial strains. “Depending on the type of bacteria, you could have different health benefits,” she says.
If you do decide to eat more fermented foods, Savary-Auzeloux recommends finding a trusted source and cautions against the do-it-yourself route. Inexpert at-home fermentation can foster harmful pathogens like Escherichia coli or Salmonella, potentially leaving you with a nasty case of food poisoning instead of a happy gut microbiome.
