Foods high in flavonoids such as blueberries and dark chocolate combined with a healthy gut could prevent the flu, a US study suggests.
An animal study published in journal Science found a particular microbe in the intestine prevented severe flu infections in mice.
The researchers at Washington University School of Medicine believe the microbe helps to break down flavonoids - a naturally occurring compound - to boost the immune system's ability to fight influenza.
"For years, flavonoids have been thought to have protective properties that help regulate the immune system to fight infections," said first author Dr Ashley Steed, who treats intensive care patients at St Louis Children's Hospital.
"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. Obviously, we need to learn more, but our results are intriguing," said Dr Steed.
As part of the study, the researchers screened human gut microbes looking for one that metabolised flavonoids.
They identified one such microbe that they suspected might protect against flu damage.
The microbe called Clostridium orbiscindens degrades flavonoids to produce a metabolite that enhances interferon, a signaling molecule critical the human immune response.
When the metabolite known as desaminotyrosine, otherwise known as DAT, was given to mice infected with influenza the mice experienced far less lung damage than mice not treated with DAT, the authors said.
The potential health benefits linked to foods rich in flavonoids - from apples and pears to dark chocolate, red wine and black tea - has been explored by nutrionists for years.
But Professor of Pathology & Immunology Thaddeus Stappenbeck says the findings show its not only having a diet loaded with flavonoids.
People also need the right microbes in the intestine to use the compound to control the immune response.
"This prevented influenza-related lung damage in the mice. It is this kind of damage that often causes significant complications such as pneumonia in people," Prof Stappenbeck said.
