A dearth of calories may not be the only reason some children face acute malnutrition, according to a new study out this week that says the microbes living in our guts may also be to blame.

Within hunger-stricken communities, not all children fare the same. Some develop acute malnutrition, while others, even their brothers and sisters, may stay healthy.

And some children respond well to treatment -- generally a peanut-based nutrient-rich supplement -- while for others, the benefits cease when the treatment does.

To figure out why this happens, researchers studied more than 300 sets of twins in Malawi, where malnutrition is a common childhood ailment, during their first three years of life.

Among half the twin pairs, one or both twins became malnourished over the course of the study.

Even among identical twins, there were cases where one twin -- but not the other -- developed a form of malnutrition called kwashiorkor, associated with swollen bellies, liver damage, skin ulcerations and loss of appetite, in addition to wasting.

That ruled out human genetics as a factor in the disorder, since identical twins share identical genomes.

But the researchers found something else at play: the microbes in the gut that extract nutrients and calories from the diet synthesize vitamins and nutrients and help shape the immune system.

When any of the twins became malnourished, both received treatment to limit food sharing.

In the healthy twin, the gut microbes thrived with the extra food and continued to mature after the treatment ended. But in the severely malnourished twin, the gut microbes stalled out or even regressed by four weeks after the treatment ended.

The findings were further bolstered when the researchers implanted into mice the gut microbes of the healthy and malnourished twins.

Both groups of mice were fed the same diet -- one similar to the nutrient-deficient diet common in Malawi -- but the ones who were transplanted with the malnourished children's microbes dropped weight, while the others did not.

"The gut microbes of malnourished children and malnourished mice do not appear to mature along a normal, healthy trajectory," said senior author Jeffrey Gordon of Washington University's Center for Genome Sciences and Systems Biology.

"Our results suggest we need to devise new strategies to repair gut microbial communities so these children can experience healthy growth and reach their full potential."

Gordon said the new findings could be a crucial step towards finding better treatment for severely malnourished children.

"It may be that earlier or longer treatment with existing or next-generation therapeutic foods will enhance our ability to repair or prevent the problems associated with malnutrition," he said.

"We are also exploring whether it is possible to supplement the therapeutic food with beneficial gut bacteria from healthy children, as a treatment to repair the gut microbiome," he added.

"We hope that these studies will provide a new way of understanding how the gut microbiome and food interact to affect the health and recovery of malnourished children."

Their study is to be published Thursday in the US journal "Science."

According to UNICEF, a person dies of starvation every 3.6 seconds, and most of the deaths are among children under five.

"Some 300 million children go to bed hungry every day. Of these only eight percent are victims of famine or other emergency situations. More than 90 per cent are suffering long-term malnourishment and micronutrient deficiency," the UN agency says on its website.