A US study reveals a new facet of the important role your gut bacteria play in protecting you from getting sick.

2017’s flu season is a nasty one: the number of cases around Australia has spiked in recent weeks. We all know you can protect against getting sick with foods that boost immunity — but eating them might be pointless if you don’t have the right combination of gut microbes to process them.

That’s the takeaway from research out of Washington University, which explores a new facet of the impact that the gut microbiome — the trillions of bacteria and other critters in the large intestine — has on overall health.

The study, published in the journal Science, found that a particular gut microbe shields mice from severe flu infections, likely because it produces a particular compound when it metabolises flavonoids.

As nutrition nerds know, flavonoids are a type of antioxidant found in plant products — including black tea, red wine and blueberries — which are known to help fight disease and inflammation by boosting the body’s ability to recover.

“For years, flavonoids have been thought to have protective properties that help regulate the immune system to fight infections,” said the study’s first author Dr Ashley L. Steed, from St Louis Children’s Hospital, in a statement.

Suspecting the gut microbiome plays a significant role in shielding against flu, Steed and her team set out to investigate what specific microbes are fighting the good fight.

They determined that a bacterium called Clostridium orbiscindens metabolises flavonoids to produce a compound dubbed DAT, which boosts a molecule called interferon that ups the immune response.

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“It’s not only having a diet rich in flavonoids — our results show you also need the right microbes in the intestine to use those flavonoids to control the immune response,” said the study’s senior author, Dr Thaddeus S. Stappenbeck.

The DAT mice still had the same levels of influenza virus infection as the non-DAT mice — but experienced far less lung damage, which often leads to severe complications like pneumonia in humans.

“The microbes and DAT didn’t prevent the flu infection itself; the mice still had the virus,” Stappenbeck said. “But the DAT kept the immune system from harming the lung tissue.”

The research could explain why different people respond so differently to the flu. Until future studies are completed, the researchers recommended eating more flavonoid-rich foods (click here for some examples).

“Flavonoids are common in our diets, so an important implication of our study is that it’s possible flavonoids work with gut microbes to protect us from flu and other viral infections,” said Steed. “Obviously, we need to learn more, but our results are intriguing.”

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