Child malnutrition has long-term effects on gut health that affect development even after treatment, a study suggests.

A team studied the gut health of malnourished children in Bangladesh.Writing in the journal Nature, they said the bacterial make-up was not fully restored to normal after food supplements were given.

They say the finding might explain why children often fail to grow normally even after treatment.

The World Health Organization estimates severe acute malnutrition affects about 20 million children worldwide.

Moderate acute malnutrition, a less serious form of the disease, is more prevalent in South Central Asia, where it affects 30 million children.

In Bangladesh, more than 40% of children under five are affected by stunted growth.

"Friendly" gut microbes play a crucial role in extracting and using nutrients in food.It has been suggested that malnutrition damages this process.Childhood malnutrition can lead to long-term problems such as stunted growth, cognitive problems and weakened immune systems.

In this study, a team at Washington University School of Medicine, St Louis, and the International Centre for Diarrhoeal Disease Research in Dhaka, the Bangladeshi capital, assessed 64 malnourished children aged from six to 20 months.

Malnourished children were either given Plumpy'Nut, an enriched peanut-based food that is the mainstay treatment for severe malnutrition worldwide, or Khichuri-Halwa, which is produced in Bangladesh and has rice and lentils as its main ingredients.Both types of food include milk powder and micronutrients, such as iron.

The researchers took faecal samples from the children before they were given the foods and every three days while they were being treated, which usually lasted for around two weeks, stopping when they reached a certain weight.Samples were then taken every month for four months.

In 50 healthy children of the same age who were studied as a comparison, the gut developed normally. But this was not the case in the malnourished children, All the children gained weight, but there was only a temporary improvement in the make-up of the gut. Once treatment was discontinued, it regressed to a more "immature" state.

Dr Sathish Subramanian, of Washington University, said: "Although therapeutic food-based interventions have resulted in a significant decline in deaths from malnutrition, many children never fully recover. "We found that children who were malnourished had gut microbial communities that were not consistent with their chronological ages.

"Moreover, the severity of a child's malnourishment was tied closely with the degree of immaturity of his or her gut microbial community, and this immaturity could not be durably repaired with standard treatments."

The authors suggest children may fare better if they are given nutritional supplements for longer, or if they are given additional gut microbes.

Commenting on the study, Prof Colin Hill of University College Cork, Ireland, said: "This is a really important and sophisticated study which focused on severely malnourished children, which further emphasises the importance of a mature diverse gut microbiota in human health.

"The findings are novel, unexpected and compelling, and show that purely nutritionally based interventions do not fully restore a mature gut microbiota in these children.

"In the future, we will recognise that restoring the health of the gut microbiota is an important precursor to restoring the health of the child."