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An egg a day might help undernourished young children grow to a healthy height, according to a six-month study in Ecuador.

Whether soft or hard-boiled, fried or whisked into an omelette, eggs appeared to give infants a boost.

It could be a cheap way to prevent stunting, say researchers in the journal Pediatrics.

The first two years of life are critical for growth and development - any stunting is largely irreversible.

Too short for age

Poor nutrition is a major cause of stunting, along with childhood infections and illnesses.

According to the World Health Organization, 155 million children under the age of five are stunted (too short for their age).

Most live in low- and middle-income countries and health experts have been looking at ways to tackle the issue.

Lora Iannotti and her colleagues set up a field experiment in the rural highlands of Ecuador and gave very young children (aged six to nine months) free eggs to eat to see if this might help.

Egg dinners

Only half of the 160 youngsters who took part in the randomised trial were fed an egg a day for six months - the others were monitored for comparison.

The researchers visited the children's families every week to make sure they were sticking to the study plan and to check for any problems or side-effects, including egg allergy.

Stunting was far less common among the egg treatment group by the end of the study - the prevalence was 47% less than in the non-egg group, even though relatively more of these egg-fed infants were considered short for their age at the start of the study.

Some of the children in the control group did eat eggs, but nowhere near as many as the treatment group.

Lead researcher Ms Iannotti said: "We were surprised by just how effective this intervention proved to be.

"And what's great is it's very affordable and accessible for populations that are especially vulnerable to hidden hunger or nutritional deficiency."

She said eggs were great food for young children with small stomachs.

"Eggs contain a combination of nutrients, which we think is important."

Balanced diet

Prof Mary Fewtrell, nutrition lead at the Royal College of Paediatrics and Child Health, said: "In a way, it is surprising that more research has not been conducted using egg in this situation - although I know that in some cultures, parents do not necessarily find egg to be an acceptable early food mainly because of concerns about allergy.

"Egg is a good nutritious complementary food that can be introduced as part of a varied diet once the mother decides to start complementary feeding - never before four months."

She said eggs should always be well cooked to avoid any potential infection risk.

The WHO recommends mothers worldwide to exclusively breastfeed infants for the child's first six months to achieve optimal growth, development and health. After the first six months, infants should be given nutritious complementary foods and continue breastfeeding up to the age of two years or beyond.

The British Nutrition Foundation advised: "While eggs are a nutritious food to include, it's very important that young children have a variety of foods in their diets. Not only is this necessary to get all the vitamins and minerals they need, but also to allow them to become familiar with a wide range of tastes and textures.

"A range of protein-rich foods should be provided when feeding young children, which can include eggs but can also feature beans, pulses, fish, especially oily fish, meat and dairy products."