When David Begg first approached pubs around the UK about the possibility of stocking non-alcoholic kombucha drinks, he was greeted with a mixture of bewilderment and defiance.

“Back then, there were still a lot of pub owners saying, ‘My pub is for people who want to drink alcohol. I want to sell beer and wine,’” says Begg, an entrepreneur who founded Real Kombucha towards the end of 2017.

Fast forward 18 months and the naturally fizzy drink, made from fermented tea, has rapidly moved from its hipster beginnings to the mainstream. After initial rejections, Begg’s kombucha range will soon be stocked in more than 1,000 pubs across the country. This change of tack is evident across the pub and bar industry, driven by a growing demand for a wider choice of non-alcoholic drinks, especially among the health-conscious millennial generation.

“There are stats showing that nearly 30% of young adults aren’t drinking alcohol,” says Neil Hinchley, director of the Crate Brewery, based in Hackney, east London, which is currently installing three new taps of home-brewed kombucha. “We certainly see that at the bar. We have people coming in and asking for the non-alcoholic drinks menu and they expect more than just orange juice, lemonade and J2O. You hear about more people wanting to go out, have a good time, but without alcohol. They want something to fill that space and kombucha ticks a lot of boxes because it has that healthy reputation. It’s had a gradual rise, but it’s now hit its tipping point.”

This tipping point has coincided with the rapid rise of fermented foods in general, a market that is expected to top £30bn by 2022, thanks to the booming wellness industry. British supermarkets now regularly stock ranges of sauerkraut and the Korean vegetable side dish kimchi, while fermented milk drinks such as kefir can be found everywhere from Tesco to fast food chain Leon. With tennis players and even Premier League footballers now swigging pickle juice mid-match to ward off muscle cramps, fermented foods have gained a foothold in the nation’s larders.

But as Hinchley points out, it isn’t just the distinctive taste that lies behind their popularity. Much of the interest has been fuelled by the explosion of media attention around the health benefits of consuming live bacteria and the array of microbes present in kimchi, kombucha and the rest has seen them branded “superfoods”.

What many consumers don’t realise is that it isn’t quite so straightforward. For while fermented foods have some proved benefits, even the most optimistic scientists admit that many of the claims being bandied around are based on somewhat flimsy science.

What do we know?

After a quick Google search, you could be forgiven for thinking that fermented foods are a cure-all. The health benefits ascribed to them include boosting the immune system, improving gut health and reducing your odds of diabetes, as well as tackling cancer, arthritis and even depression.

“There’s a lot of hype,” cautions Maria Marco, professor of food science and technology at the University of California, Davis. “There are some general properties of these foods that could conceivably have an impact on our body, and perhaps help the immune system, but they’re not drugs. It’s ridiculous to think that they could treat diseases like cancer.”

Right now, the only clinical benefit accepted by the European Food Safety Authority is that fermented dairy products are suitable for people with lactose intolerance, because the bacteria within them break down the lactose in milk as part of the fermentation process. As fermentation is a form of predigestion, these foods are also thought to be more easily processed by people with irritable bowel syndrome or digestive issues.

But digestion aside, scientists have so far struggled to demonstrate a clear cause and effect between consuming fermented food and improved health. Much of the media excitement has revolved around the supposed ability of these foods to improve the balance of healthy bacteria in the gut, but in reality microbiologists say that a few spoonfuls of yoghurt or kimchi will make little or no difference to this vast colony of microbes.

“Inside our gut, each of us has at least 100tn microbes,” says Prof Zhaoping Li, head of clinical nutrition at the University of California, Los Angeles. “Even if one of these foods contains 100m microbes, it’s very trivial in comparison. Many of them will be killed when passing through our stomach and if they make it to the gut, it’s not touching anything.”

Real Kombucha being poured in a Fuller’s pub

Limited evidence

Despite the “superfood” tagline, many fermented food manufacturers focus on the sensory and sophistication angles when promoting their products, rather than the health side of things. This is largely because of a sparsity of human evidence. The studies that claim different fermented products have anticancer properties, or the ability to control cholesterol and hypertension, have mostly been carried out on laboratory animals or individual cell lines.

Only a few clinical trials have investigated whether consuming fermented products can have a beneficial effect on health metrics such as blood pressure or insulin resistance. These have so far returned mixed results, with the studies often containing severe flaws in their design.

“They’re typically looking at something like blood pressure over 21 or 28 days,” says Robert Hutkins, a professor at the University of Nebraska-Lincoln who researches the link between fermented foods and human health. “But blood pressure varies ordinarily, so you really need to study it over 90 or 120 days to have any idea if there’s a significant change.”

Most of the other claims have come from population studies that compare parts of the world where people eat a high proportion of fermented foods with places where they don’t and analyse the relative prevalence of different diseases. But these types of studies are vague and notoriously difficult to interpret.

“Koreans have a lower risk factor for bowel disease than Americans,” Li says, “but that isn’t necessarily because they eat more fermented foods. It could be genetics or because they eat more fish or the fact that overeating is less common. There are so many potential confounding factors at play.”

Lack of regulation

Because the rise in popularity in fermented foods in the UK is a relatively recent phenomenon, the industry is in many ways, a bit of a wild west. Hutkins admits that most of the clinical trials conducted on these foods have been funded directly by the companies trying to sell them, such as Danone or Nestlé, while there’s currently little or no regulation covering the labelling or manufacturing process of fermented products.

As a result, scientists say that fermented foods found on supermarket shelves can have high sugar or sodium contents. Many also contain large amounts of preservatives, meaning that customers are sometimes buying expensive milk or cabbage that doesn’t contain any live microbes.

Anybody can stick ‘probiotic’ on their label without identifying which bacteria are in the food

“It’s not always clear from the packaging but in general, the more processing that’s been done, the worse the product is,” says Dr Paul Cotter, head of food biosciences at the Irish Agricultural and Food Development Authority Teagasc’s food research centre in County Cork. “Steps need to be introduced so that if a product claims to be kefir or kombucha, it must have the associated living microbes in there and be made in a certain way.”

One common claim on fermented food labels is that they contain probiotic organisms, specific microbial strains that have a proved health benefit. But in reality, relatively few products are tested to find out the precise types of bacteria that are present.

“It’s a little bit problematic that anybody can stick ‘probiotic’ on their label without having to identify what species of bacteria are in the food,” Marco says. “It signals that it’s healthy, but we don’t necessarily know that those particular microbes are ones we would define as probiotic.”

Change may be on the cards, however. Such is the interest in fermented foods that governing bodies have been forced to get involved, particularly in the US, where sales of kombucha are growing at a faster rate than any other soft drink. The National Institute of Health is currently funding clinical trials into various fermented products and there are high hopes that this will yield more concrete information on their health benefits in the next five to 10 years. “This will be very interesting,” Hutkins says. “If it’s funded by the government, then the results are publishable, no matter what they find.”

And while much has been written about the potential of fermented foods to have an impact on what bacteria live in our guts, Marco believes any notable benefit may instead come from their interactions with the small intestine, possibly by stimulating the immune system and preventing toxins from getting into the bloodstream. “There’s a possibility that the microbes in these foods could directly impact the intestinal cells,” she says. “There’s far fewer microbes there compared to the gut and also a lot more exposure to our food. It also happens to be the place where most of our immune cells are.”

If there do turn out to be any clear benefits, scientists say we should still expect them to be relatively small. Eating a balanced diet, minimising stress levels and getting good quality sleep all have a far greater effect on our body as a whole than any single food. “Consuming fermented foods instead of highly processed foods or drinking something like Coca-Cola is probably better for you, but that alone is not going to make a huge change to your health,” Li says. “It’s all relative. No food is going to have a dramatic, wide-ranging effect on the body, like a drug, unless you make wholesale changes to your diet.”

Not that kombucha makers are concerned. With a variety of brands and flavour profiles pouring into the market, they believe that the only trajectory is up. “I think it will become an expected part of people’s night out,” Hinchley says. “People now expect the same offering and range they have in coffee and beer, in soft drinks. And kombucha, I think, is going to continue to lead the way.”