A daily serving of traditional dairy kefir benefits the gut microbiome more than a probiotic-fortified yoghurt drink or an inulin-rich diet, according a recent clinical study.
As scientific understanding on the importance of the gut microbiome on overall health grows – it is known to impact immunity, digestion, mood, eye health, and more –consumer interest in food and drink products that benefit gut health is on the rise.
The popularity of probiotics, prebiotics, and traditional fermented foods such as kefir, kombucha, and sauerkraut has risen significantly in recent years.
“With the widespread acceptance of such food in the form of yoghurt, kimchi and juices, there is ample opportunity [for brands] to explore the use of pre-and probiotics for gut and cognitive health,” write market research analysts at Mintel.
However, an open access study published in the peer-reviewed Nature journal suggests that kefir may be the most effective.
Kefir is a traditional fermented dairy drink originally from the Caucasus region of Europe that is made from just two ingredients: milk and kefir grains composed of yeast and lactic acid bacteria. It has a thick and creamy texture thanks to the fermentation process and contains live probiotic bacteria. It has been associated with anti-cholesterolemic, anti-inflammatory, and anti-pathogenic effects.
Probiotics – defined as live microorganisms that exert health benefits upon the host when ingested in sufficient quantities – can be taken in supplement form or via fortified foods. Human studies have shown that some probiotic strains, such as Bifidobacterium infantis 35624, Lacticaseibacillus casei DN-114001, and Lacticaseibacillus casei Shirota, have health benefits, such as relieving symptoms of irritable bowel syndrome (IBS) or protecting against infections.
Inulin, meanwhile, is a prebiotic soluble fibre that nourishes the bacteria in the gut, promotes digestive health, and impacts blood glucose levels. Inulin is naturally present in fruit and vegetables and some manufacturers fortify products with inulin as a sugar reduction strategy – although some research has shown that a high intake of inulin can reduce the diversity of gut microbes by feeding and promoting the growth of select bacteria only.
In this Nature study, the researchers divided healthy adults into one of three groups – inulin, kefir, or probiotics – and compared the impact of consuming these foods for one month on their gut microbiome and urine metabolome.
Participants in the inulin group ate extra portions of fibre-rich fruits and vegetables, amounting to 7 g of natural inulin with a minimum daily dose of 5 g while those in the kefir group drank one drink a day made by the UK brand Nourish Kefir. Individuals in the probiotic group drank a daily probiotic drinking yoghurt made by Yakult containing a minimum of 2 × 1010 colony forming units (CFUs) of L. casei Shirota.
The researchers tested stool samples before and after the intervention, including for the bacterial species they expected to be altered, such as the strains in the probiotic Yakult drink.
They found no significant changes in microbial diversity and no differentially abundant species in the probiotic or inulin group but noted an increased abundance of the species Lactococcus raffinolactis and a corresponding altered urine metabolome in the kefir group.
“Overall, our results indicated that daily consumption of a single portion of kefir alone resulted in detectable changes to the gut microbiota and metabolome of consumers,” they concluded.
Detecting Lc. raffinolactis in the kefir group was of particular interest, they wrote, because it has a “non-dominant” status compared to other lactococci in dairy foods. None of the three products resulted in significant changes to the clinical parameters or biomarkers that were tested – body fat, anxiety, and abdominal symptoms –, although they noted this may be due to the study’s small size.
The researchers added: “Ultimately, this study highlights the need to employ deep metagenomics sequencing in larger cohorts to examine the potentially colonising microbial members of ‘live foods’.”
Commenting on the study, Dr Frank Bernier, senior manager of microbiome biotech company Bio Palette and review editor of the journal Frontiers in Aging Neuroscience, noted in a Linkedin post that, of the three interventions, kefir “emerged as a standout” for gut health.
“The takeaway? A daily dose of kefir might be all it takes to make detectable changes to one's gut microbiota and metabolome. A fascinating insight for those considering their next health drink!”
Dr Tim Spector, leading microbiome researcher, professor of genetic epidemiology at King’s College London, and co-founder of personalised nutrition company Zoe, has also highlighted the gut health benefits of kefir in the past, writing that he has cut out milk from his diet apart from a small daily serving of kefir.
Despite the growing popularity of products promoting gut health, Mike Hughes, head of insights and research at FMCG Gurus, warns that brands should not overestimate how willing consumers are to make dietary changes for health reasons.
During a recent Fi Global Insights webinar on gut health, he said: “Consumers want products that contribute to their long-term health, but they realise dieting is a challenge and don’t want to make fundamental changes that involve a sacrifice. If brands can launch products that have science-backed claims and can be easily incorporated into their diets, they will be more appealing to consumers.”
“It is about assisting consumers with products that make them think: ‘this is a relatively easy and straightforward way to boost my health over the long term’.”
Many kefir products on the market cater to this desire for convenience. The most common formats are ready-to-drink kefir and ready-to-eat spoonable kefir pots, with brands differentiating themselves by offering flavoured versions or using cow’s milk, sheep’s milk, or goat’s milk as the dairy base. Some brands, such as US company Desert Farms and Australian brand Humpalicious, make camel milk kefir.
Canadian brand President’s Choice recently launched a plain kefir probiotic fermented milk made with 12 different bacterial cultures and marketed the product as “an easy way to enjoy the benefits of probiotics”.
Some manufacturers are also experimenting with launches in other categories. In August this year, Lithuanian manufacturer HKScan launched meat shaslik (kebab) in a kefir marinade under its Rakvere brand – although heating kefir during the cooking process destroys the beneficial bacteria.
