The bacteria in your microbiome are shaped by your family, friends, pets and lovers

When we are born, we get most of our gut microbes from our mothers (see “Where does your gut microbiome really come from – and does it matter?”). But as we get older and form other close relationships, including with intimate partners, friends and pets, we start to pick up their microbes too. This could potentially affect our risk of developing conditions like obesity, inflammatory bowel disease, asthma and allergies (see “What is the role of the microbiome in diseases like chronic fatigue?”).

“I jokingly say that your dating app profile should include your microbiome profile,” says Brett Finlay at the University of British Columbia in Canada.

The strongest evidence comes from work published in January by Mireia Valles-Colomer at the University of Trento, Italy, and her colleagues, who conducted the largest study to date of how our gut microbiomes are shaped by the people around us. They analysed DNA in the faeces of more than 7000 people from households around the world, including rural parts of Africa and South America and cities in the US, Europe and China, to find out which bacterial strains were in their guts and what proportion they shared with others.

Bacterial strains are slight genetic variants of the same bacterial species and are highly individualised, meaning if two people share a strain, it must have been directly transmitted between them. As expected, infants under the age of 1 and their mothers shared the most …