Anorexia has the highest mortality rate of any mental illness, and yet we still know frustratingly little about what triggers the condition, and how to successfully treat it. But scientists now think that might be because we've been looking in the wrong place this whole time.

A team of leading medical researchers in the UK has just published a paper suggesting that anorexia originates from a bacterial infection, rather than being a purely psychological condition. And they think chronic fatigue and irritable bowel syndrome could be caused by the same thing.

"Psychological factors might be important, but are unconvincing as the primary or major cause," swrite the researchers, including Jim Morris from the University Hospitals of Morecambe Bay in northwest England, and Sue Broughton and Quenton Wessels from Lancaster University.

The paper has been published in the journal Medical Hypothesesand, as the name of the journal suggests, this is nothing more than a hypothesis waiting to be tested for now.

But if confirmed, it could lead to new treatments for the conditions, and some much-needed hope for people living with anorexia, irritable bowel syndrome, and chronic fatigue.

The researchers present a pretty compelling case. While they haven't narrowed down the initial bacterial cause, the idea is that a patient's immune system creates antibodies to fight off an initial bacterial infection, but those antibodies then become confused, and start to attack the patient's own nerve cells instead.

This autoimmune attack could explain the symptoms experienced by people across all three conditions: anorexia, irritable bowel syndrome, and chronic fatigue. And it could also explain the immense imbalance of rates between males and females, seeing as women are already known to be at an increased risk of developing other autoimmune conditions.

"The female to male ratio in these conditions is of the order of 10," the researchers write. "The female excess in irritable bowel syndrome, chronic fatigue syndrome, and anorexia nervosa is equally extreme, and therefore this fits with the idea that auto-antibodies to nerve cells could be part of the pathogenesis of these conditions." 

The bacteria hypothesis can also explain some of the specific symptoms of anorexia, which many of us associate with the influence of models and the fashion world on young women.

"Auto-antibodies acting on the (brain's) limbic system could induce extremes of emotion including disgust and fear," write the scientists. "These then become linked, in the minds of adolescent girls, to culturally determined ideas of what is, and what is not, the ideal body shape and size. It is then a small step for disgust and fear to be directed to food and obesity which the fashion industry currently demonises."

If the condition is determined to have a bacterial origin, that means that anorexia could also be contagious. But the researchers argue that social factors are still likely to play a role in who develops the illness and who doesn't. 

"There might, for instance, be an increased incidence of physical and sexual abuse in childhood in those who go on to manifest functional disorders," they write. "It is easy to see how this could influence symptoms in adults but it stretches credulity to imagine abuse as the sole and sufficient cause of the functional disorder."

The team will now test their hypothesis on animal models in the lab, and will try to identify the bacteria responsible for confusing the immune system into attacking the body's own nerves.

"If we can isolate the culprits perhaps we can restore the correct bacterial balance," Wessels told The Telegraph. "We hope to move into the lab over the summer, and hopefully have an answer by the end of the year."

If they find evidence to support their hypothesis, it will be a case of working out how to eliminate the bacteria that are triggering these auto-antibodies, as well as getting rid of the auto-antibodies themselves, potentially through healthy blood transfusions.

Watch this space for updates on the research.