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Anorexia may be linked to the balance of bacteria in the gut, new research suggests.

People with the eating disorder have fewer and less diverse communities of microbes in their digestive tracts compared to those without the disorder, the study found.

This imbalance could be associated with some of the psychological symptoms of the condition, such as depression, anxiety and further desire for weight loss, the researchers said.

Previous studies have linked the gut microbiota - the trillions of bacteria that affect digestive health and immunity - with brain health.

The new findings suggest microbes in the intestinal tract may affect the 'gut-brain axis', the researchers said.

This is the biochemical signaling that takes place between the gastrointestinal tract and the nervous system, which plays an important role in healthy brain function.

Gut bacteria are involved in this signalling, and so an imbalance in bacteria could affect the brain.

Serious eating disorders such as anorexia, bulimia and binge-eating disorders affect an estimated 5 per cent of women and 2 per cent of men in the UK.

In the US, three million people are affected by anorexia.

The condition has the highest death rate of any psychological disorder, as sufferers usually die from malnutrition or suicide.

The study's author, Dr Ian Carroll, of the University of North Carolina (UNC) Center for Gastrointestinal Biology and Disease, said previous studies had linked gut bacteria to weight and behaviour.

Since people with anorexia exhibit extreme weight loss, he decided to study the relationship further.

Dr Carroll said:
'We're not able to say a gut bacterial imbalance causes the symptoms of anorexia nervosa, including associated symptoms, such as anxiety and depression.

'But the severe limitation of nutritional intake at the center of anorexia nervosa could change the composition of the gut microbial community.

'These changes could contribute to the anxiety, depression, and further weight loss of people with the disorder.

'It's a vicious cycle, and we want to see if we can help patients avoid or reverse that phenomenon.

'We want to know if altering their gut microbiota could help them with weight maintenance and mood stabilization over time'
As part of the study, Dr Carroll's team collected fecal samples from 16 women with anorexia after they were first admitted into the UNC Center of Excellence for Eating Disorders.

They then took samples again after they had received treatment and were discharged, which typically happens when they have regained 85 per cent of their goal body weight.

They also took samples from 12 individuals without the disorder, for comparison.

Then, they recorded the composition and diversity of the gut microbiota in each sample.

They found significant changes in gut bacteria populations between admission and discharge.

The samples taken at clinic admission had fewer different types of bacteria, meaning the intestinal communities were much less diverse.

When they were discharged from hospital, the diversity of bacteria in the gut had increased, but was still significantly less diverse than that of 12 healthy individuals.

Microbial diversity in the gut is a sign of better overall health, the researchers explained.

As the microbial communities in patients with anorexia improved during clinical care and weight gain, the moods of patients also improved.

Thus, the researchers noted an association between the gut microbiota and a central symptom of people with anorexia.

The question remains whether improving microbial abundance and diversity could help relieve symptoms related to the eating disorder.

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People with anorexia were found to have fewer and less diverse communities of bacteria in their gut. This could be linked to psychological symptoms of the condition, including depression and anxiety, experts said
To find out, Dr Carroll has formed a team of researchers and have received a five-year, $2.5 million (£1.6 million) grant from the National Institutes of Mental Health to further study the relationship between the gut microbiota and anorexia.

He plans to use the grant to take samples of gut bacteria from people with anorexia and put them into germ-free mice.

This will help him learn how they affect the biology and behavior of the mice.

If he discovers they have a detrimental effect on the mice, this suggests that a possible way of treating anorexia could be to help sufferers cultivate a healthy balance of gut bacteria.

'We're not saying that altering gut bacteria will be the magic bullet for people with anorexia nervosa,' Dr Carroll said.

'Other important factors are at play, obviously. But the gut microbiota is clearly important for a variety of health and brain-related issues in humans. And it could be important for people with anorexia nervosa.'

The research was published in the journal Psychosomatic Medicine.