The theory that the trillions of microbes living in the human gut are in constant communication with the brain affecting the way a person feels has been strengthened thanks to the increasing prevalence of faecal transplants.

Anecdotal evidence that recipients of a faecal transplant - a procedure to restore the gut microbiota - mimick the mood and other characteristics of their donor will be presented at the Royal Australasians College of Physicians (RACP) annual Congress in Melbourne on Tuesday.

Associate Professor Patrick Charles from the Department of Infectious Diseases at Austin Health says they have heard of some "very interesting" things from faecal transplant recipients, including stories about patients experiencing fluctuations in mood.

"There have even been reports that patients with no prior history of depression have become depressed after receiving a transplant from someone with depression," he said.

"There have also been cases where dramatic body changes have occurred - both rapid weight gain and weight loss, each time aligned to the donor."

A faecal microbiota transplant, sometimes known as an FMT, is a procedure which replaces the 'gut bacteria' in an unhealthy individual with those of someone who is healthy.

Essentially, it involves taking 'healthy' poo from a donor and using it to create a liquid preparation that is then transplanted into the patient, normally via a colonoscopy.

It is becoming increasingly popular for the treatment of multiple conditions including chronic fatigue, irritable bowel syndrome, Parkinson's and autism.

Typically its performed to treat someone with Clostridium difficile infections when antibiotics fail.

Despite more research being needed, Ass Prof Charles says its only now that scientists are beginning to recognise and understand the influence of the microbiome on both the mind and body.

"We're still really only just scratching the surface of what impacts microbiomes have on health and disease but as DNA sequencing techniques advance so will our understanding of their role," he said.