The popularity of kombucha and other fermented foods, like kefir, kimchi and tempeh, has risen on the back of research which shows gut health is closely linked to general, overall health.
"We carry around about two kilos of bugs, each of us, which is kind of gross, but kind of cool," food and nutrition writer Niki Bezzant told Healthy or Hoax host Stacey Morrison, "Scientists used to think that those bugs were just sitting there benignly. Now what they know is that those bugs are very active and they can do a lot in our bodies and they are actually responsible for a whole lot to do with just about every aspect of our health."
Bezzant said as well as a general health halo, probiotic and fermented foods also have this veneer of ancient, exotic wisdom because they've been used in many, many cultures for thousands of years.
Food is fermented when bacteria or yeast pre-digest it and there are lots of different types of fermented foods.
Dr Megan Rossi is a research fellow at King's College London and the author of Eat Yourself Healthy, a "bit of a bible to gut health."
She said there are essentially three different 'mechanisms' for how fermented foods can be beneficial.
"Some fermented foods actually give us the live microbes, like kombucha," said Rossi, "Some just give off healthy chemicals and some break down other elements of foods we call anti-nutrients, which aren't necessarily dangerous but they reduce our ability to absorb some nutrients."
It is not easy to tell if you have a healthy gut, but there are some clues.
"One of the key ones is, are you having regular gut symptoms like constipation, diarrhea, bloating?"
But Dr Rossi said just because you don't have those symptoms doesn't mean you have good gut health.
"So it's things like, how often are you getting sick? Are you really stressed? How much sleep are you having? Are you following a restrictive diet? Do you have family history of a different disease or are you on medications?
"All of those factors combined really give us a more holistic idea of your gut health," she said.
And with the Covid-19 pandemic still raging, Dr Rossi said now is the perfect time to be checking in on your gut health, because 70 percent of our immune system sits along our nine metre digestive tract.
"There are some researchers that are currently looking at specific types of probiotics and live bacteria and whether they could have a role in Covid," said Rossi.
In a sunny, wood-paneled bar in Ponsonby, Auckland, Derek Hillen espouses the benefits of a fermented tea drink.
His bar, New Leaf Taproom, doesn't serve beer, instead it has kombucha on tap.
Kombucha is made with the four basic ingredients: Water, tea, sugar and culture.
"Most people don’t realise the ancient origins of this drink and they think it’s some new hipster thing," said Hillen, "But it isn’t. It’s only recently that people have been experimenting and adding different juices and flavours and colourings to it."
"I think we're at the very beginnings of it becoming a mainstream stream drink and supplanting soda," said Hillen.
And he is confident kombucha’s popularity is going to continue to rise.
"More and more people are finding out about it and especially among millennials there's a very strong movement against drinking alcohol, so people are looking for healthy substitutes and Kombucha certainly fits that."
"A lot of our customers are vegan or vegetarian or into yoga. Generally, healthy people seek this type of thing."
But Hillen says not all kombucha is created equal. Some of the exported brews are not brewed properly, the probiotics are injected just before bottling and they use fake sugar substitutes or add sugar.
"If you see a lot of ingredients on any product that you're about to eat with long names that you can't pronounce, maybe you should buy something else," advised Hillen.
Niki Bezzant agreed. "Even if it's kombucha, it’s still a sugary drink if it's got a couple of teaspoons of sugar inside. So you want to pay a bit of attention to that."
Dr Megan Rossi and her team at King's College in London recently did a review paper on studies into the health benefits of fermented foods. They did not find a lot of science to back up the health claims around it.
"I think the fermented food world is very interesting, but I don't think they're going to be a miraculous cure," she said.
We shouldn't be fooled into thinking we have to pay large amounts of money to have these fermented foods in our diet. I think they're are really nice add, eat them if you enjoy the taste and the flavours, but don’t think you have to have them to have a healthy gut."
Dr Rossi said there has been some really amazing research showing dietary fibre - which has the sole purpose of feeding our gut bacteria - can have huge health benefits.
She said the study showed for every eight grams of dietary fiber per day on a population level, we could reduce our risk of type two diabetes by 15 percent, our risk of heart disease by 18 percent, and our risk of colon cancer by nine percent.
"And that's just with eight grams of fiber, which is like a can of beans, of legumes or some veggie sticks and some humous," said Rossi.
"Kimchi and sauerkraut also contain the dietary fiber. So it's a bit of a double win. Why not have the kimchi and sauerkraut, which not only contain the dietary fiber, but potentially also contain some of those live microbes which may populate our gut and do beneficial things."
Dr Rossi gives fermented food a Healthy or Hoax rating of 2.5 stars.
Listen to the full podcast for more information on gut health and probiotics and a taste test of New Leaf's brews, plus tips on how to make your own kombucha.
Some of research papers reviewed for this podcast are below.