Supercentenarians – humans who live beyond 110 years of age – are objects of great fascination in our death-fearing culture. Interviews with them inevitably demand to know that one simple ingredient that is the secret to their extraordinary longevity; was it a shot of whisky before bedtime, maintaining good friendships, a happy marriage or always having a pet?

In the case of Spain’s Maria Branyas Morera – who was the world’s oldest person until she died at the very ripe old age of 117 last year – one possible answer to that question was yoghurt.

The study attempting to get to the bottom of Branyas’s biological good fortune revealed that for the last couple of decades of her life, she ate three serves of yoghurt a day. Analysis of her gut microbiome showed unusually high numbers of a beneficial bacteria known as bifidobacterium, which can be boosted by yoghurt consumption, and a “microbiome that confers an increased likelihood for a healthy extended lifespan”, the researchers wrote.

Before you rush out to your nearest supermarket and load a trolley with fermented dairy, there are a few things to know about Branyas and yoghurt.

The first is she did a lot of things right, not just the yoghurt, says gastroenterologist Professor Emad El-Omar, director of the University of New South Wales Microbiome Research Centre at St George hospital in Sydney.

She ate a Mediterranean diet, which is high in vegetables and fruit, wholegrains, legumes, nuts and seeds, and low in processed foods, red meat, added sugar and refined grains. This diet also provides exactly the right complex carbohydrates, dietary fibre and other nutrients for beneficial gut bacteria to thrive on.

“The Mediterranean diet is probably the healthiest diet in terms of its composition and how it feeds the microbiome,” El-Omar says. “If you’re eating a healthy diet and living a healthy lifestyle, that is reflected in the composition and the function of your microbiome, which then works for you instead of against you.”

Branyas didn’t smoke or drink alcohol, she exercised regularly, and spent lots of quality time with friends and family.

And she had good genes. “She did the first thing right – she got the right parents,” says nutritionist Professor Clare Collins from the University of Newcastle. “She probably lived on a small island, no car, eating lots of seafood, walking up and down the hills, eating vegetables from the local market, and then adapting her dietary patterns as she went.”

So what role, if any, might yoghurt have played in Branyas’s staying power?

Yoghurt is interesting because it has live bacteria in it, and in particular a type called lactobacillus, says Associate Professor Claus Christophersen, a microbiologist at Edith Cowan University in Perth. This is one of the bacteria that turns milk into yoghurt, by feeding on the milk carbohydrates to produce lactic acid during the fermentation process, which then causes the milk proteins to coagulate.

Lactobacillus are also important bacteria for good gut health, although we generally have low levels of them, he says.

“If you have more of them, you tend to drop your pH in your gut, which is a good thing, so that actually keeps pathogens at bay a little bit easier, and it favours more of your beneficial bacteria if your pH is a little bit lower,” Christophersen explains.

Lactobacillus also appear to have beneficial effects on the immune system.

“When we talk about gut health, we often talk about the large intestine, where the bacteria grows,” Christophersen says. “But in the small intestine is where there’s lots of connection with the immune system.”

There’s also evidence that beneficial gut bacteria produce their own antimicrobial substances that help suppress the growth of harmful bacteria, El-Omar says.

“They’re essentially keeping away the nasty guys and allowing that coexistence and natural balance that protects you from infections,” he says.

And increasingly, scientists are coming to understand the positive interactions between the gut microbiome and a range of other body systems, including the brain.

Yoghurt is also a good source of these beneficial bacteria because the dairy fats help protect the bacteria from the highly acidic stomach environment, so they can pass through and into the small and large intestine.

But not all yoghurt is created equal. “It’s yoghurt with live microbes in it, and it’s not squeezy-pouch yoghurt with acidity regulators and preservatives or colours and flavours,” Collin says.

The dairy section of any supermarket is filled with a dazzling array of yoghurt choices, so Collins recommends choosing carefully. “You’ve got to go to the supermarket going, ‘I’m standing in the yoghurt aisle today, and I’m going to take my time’,” she says. That includes looking at labels and ruling out the products with lots of numbers – which represent the chemical additives – in the ingredients list.

“Or you can just buy plain Greek yoghurt and just grin and bear it when you eat it and it’s really tart, or eat it with a bit of fruit added to it, or a bit of cinnamon on top, or something like that,” Collins says.

Once you’ve got your good yoghurt, it also helps to eat it regularly, like Branyas did. “She was having it three times a day; she would have been getting her microbiome community topped up repeatedly all day,” Collins says.