When children are starving, the bacteria that live in their intestines may determine whether they can be saved, scientists working in Bangladesh are reporting. And they say it may become imperative to find a way to give children bacteria as well as food.

The study, done by researchers from Washington University School of Medicine in St. Louis and the International Center for Diarrheal Disease Research in Dhaka, the Bangladeshi capital, was published by Nature last week.

Trillions of bacteria in the human gut help digest food and produce vitamins, and they amount to “a microbial organ within an organ,” said Dr. Jeffrey I. Gordon, an author of the paper. It takes up to about age 3 for a child to get all the species that seem to be needed, he said.

But stool samples showed that severely malnourished children often lack the needed species and do not acquire them even when they are fed nutrition-dense therapeutic foods like the peanut-based Plumpy’Nut or lentil-based porridges for weeks. As a result, they may remain stunted and mentally handicapped although they are getting enough calories to live.