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Forget Kombucha, Miso and Matcha. The latest superfood export that's hot property at Asian supermarkets everywhere is nattō - fermented beans which are quickly becoming a TikTok sensation.
Sticky and slimy, the meal may just be the world's most polarising breakfast due to its unpleasant ammonia-like smell.
However, it's eaten by nearly 80 per cent of the Japanese population, usually over a bowl of steaming rice.
For centuries, it's been hailed as a nutritional powerhouse – believed to be linked to reduced risk of stroke, bone diseases and, most intriguingly, tooth loss.
And now the Western hemisphere is catching up.
Trade data shows Japan's exports of nattō have tripled since 2017, with taste test videos on TikTok raking in hundreds of thousands of views.
While a growing body of research seems to have proven the dish's supposed health benefits, experts have told the Daily Mail of significant risks for specific cohorts.
So should you be swapping your scrambled eggs for breakfast nattō? Here, experts reveal all about the stinky superfood...
Stinky, sticky and slimy, fermented bean dish natto may just be the world's most polarising superfood
What is nattō?
First introduced in Japan in the 700s, nattō became a popular dish amongst aristocrats and warriors alike during the 1100s – later serving as an important part of Buddhist vegetarian cuisine from the 1300s–1500s, alongside tofu.
By the Edo period, from 1603–1867, nattō was a staple in most Japanese households – appearing in cookbooks and usually prepared at home.
To make the dish, soybeans were soaked in water, boiled or steamed, and blended with bacteria to ferment them.
Historically they were then wrapped in straw and left to ferment for about a day – depending on the season and temperature.
Today, however, nattō can be purchased ready–made from convenience stores and supermarkets across Japan.
In the UK, nattō is often sold at Japanese or Asian supermarkets, and can be ordered online. Around 100g of the beans – or two servings – costs around £5.
Shop–bought nattō usually comes in small single–serving polystyrene foam containers, alongside a tiny packet of soy sauce and hot mustard, and is eaten cold.
Nattō is typically eaten in Japan for breakfast, with a raw egg and often on a bowl of steaming rice (pictured, a traditional Japanese breakfast)
A standard 50g serving of nattō is a dieter's friend due to the low calorie count (110), while packing in 10g of filling protein with virtually no salt.
Another benefit is the 5.4g of fibre - the equivalent of roughly two bananas and a fifth of your recommended daily intake.
The dish is also exceptionally rich in key micronutrients, like calcium, potassium, iron, manganese and vitamin K2, as well as vitamin B6 and vitamin E.
This boasts benefits for bone health, blood flow and the elasticity in our skin, as well as oral health.
The dish's reputation as a nutritional powerhouse comes from its impressive combination of protein, fibre, healthy fats, vitamins, minerals and other naturally occurring compounds, says London–based dentist Dr Soumaya Zinet.
'They're all found in a relatively small serving,' she explains.
'Nattō is particularly rich in MK–7, a form of vitamin K2. Vitamin K is needed for normal blood clotting and also contributes to the maintenance of normal bones.
'Fermentation also produces nattokinase, an enzyme that has been studied for its possible role in breaking down fibrin, a protein found in blood clots.'
A natural way to lower blood pressure
Fermented foods are known for helping to fuel and create healthy bacteria in the gut - the microbes that are linked to the prevention of a host of chronic diseases.
But nattō's health benefits appear to go far beyond the digestive system.
Research shows the dish can help improve heart health, strengthen bones and even lower blood pressure.
Clinical studies have shown that the key enzyme found in nattō – nattokinase – can help break down blood clots and supports healthy blood circulation.
A 2022 paper from researchers in Pakistan found that eating the fermented beans could help lower and manage high blood pressure.
And a long–term study published in the British Medical Journal in 2020, carried out by researchers at the National Cancer Centre in Tokyo, found that men and women who ate fermented soy–based foods like nattō daily reduced their risk of dying from a stroke or heart attack by 10 per cent.
Nattō's uniquely high levels of vitamin K2 mean the dish also holds impressive benefits for bone health.
Studies on postmenopausal women have shown that regular nattō intake both improves bone mineral density and helps to prevent bone fractures.
Its high levels of key bone–strengthening nutrients can also have an indirect effect on the teeth, says dentist Dr Zinet.
'Nattō provides calcium and phosphorus, which are important components of bones and teeth,' she says.
'Vitamin K also contributes to normal bone health. This matters because our teeth depend on healthy bone around them.'
But for some people, there are serious risks
For many, the main deterrent of nattō is likely to be its relatively strong smell and sticky texture, which can take some getting used to.
But experts warn that some should steer clear of the fermented beans no matter what.
'Of course, anyone with a soya allergy should avoid nattō, and like other beans, it can cause temporary bloating or wind, particularly if someone is not used to eating them,' says Dr Zinet.
'But the main medical caution is for anyone taking warfarin or another vitamin K antagonist.
'Nattō is very high in vitamin K, so anyone taking these medicines should speak to their doctor before making a significant change to how much natto they eat.'
An overdose of vitamin K can cause liver problems, as well as difficulty breathing and issues with blood clotting.
'Finally, because nattō is sticky, it can be harder to clear from around fixed braces or other dental appliances.
'Rinsing with water after the meal and cleaning carefully will help remove any remnants.'