You will have heard the saying ‘you are what you eat’.
But even the man who made it up more than 150 years ago may not have realised how true it is.
Scientists have now uncovered the first evidence of bacteria living in the human brain, suggesting it got there by travelling through the bloodstream from the gut.
The discovery, made by chance after analysing brains of deceased humans, has been branded ‘mind-blowing’ and ‘revolutionary’.
The University of Alabama at Birmingham researchers presented their findings at a major convention in San Diego last week.
Scientists from the University of Alabama say they have found the first evidence of bacteria from the gut travelling to the brain and living there – pictured, one of Dr Roberts’ microscope slides showing the oval-shaped bacteria to the left of the much larger dark-grey blood cell
The study was originally designed to compare the differences between brains of mentally healthy people and schizophrenics.
If confirmed in further trials, the findings could pave the way for a whole new route of research investigating how bacteria can affect our brains.
The brain is protected from bacteria and viruses by a membrane around it and, until now, it has been believed that anything making it through the membrane would cause serious illness.
Dr Ronald McGregor, from the University of California at LA, who was not involved with the research, described the finding as ‘mind-blowing’.
In an interview with Science, Dr McGregor said: ‘It’s like a whole new molecular factory [in the brain] with its own needs.’
Bacteria in our gut is known to affect the health of the rest of our bodies, potentially controlling our weight, disease risk and even linking to anxiety and depression.
Research published in June by Harvard Medical School branded the gut a ‘second brain’ because of how it affects our mood.
OBESITY FUELS DEPRESSION BY CHANGING GUT BACTERIA
Obesity makes people more anxious and depressed by changing the bacteria in the gut – our ‘second brain’ – research suggested in June.
Scientists found a high fat diet alters the type of bacteria that live in the gut and these play a role in mental disorders.
Obese people and those with type 2 diabetes suffer more negative feelings that others, but scientists have not previously been able to work out why this happens.
Researchers at Harvard Medical School discovered that mice fed a high-fat diet showed significantly anxious, depressive and obsessive behaviors than those on regular diets – but treating their gut bacteria with antibiotics improved their moods.
Even without altering their diets, once the mice were given antibiotics to alter the gut bacteria the symptoms completely ceased or were reduced.
This study was one of the latest to show that mental health and obesity affect one another.
These discoveries underscore the ‘gut-brain’ connection, the researchers said.
But it may be the same bacteria affecting both our gut and our actual brain when it travels through the blood stream, if the research is accurate.
The scientists, led by Dr Rosalinda Roberts, have emphasised the fact their work has not yet been checked by other experts.
And they warned the 34 brains they tested could have been contaminated because they were all dead.
However, the way the bacteria were distributed throughout the brains – and the fact they were present in every single one – suggest this was no accident.
Dr Roberts kept finding rod-shaped samples in her microscope slides but ignored them at first because she was looking for something else.
But after noticing they popped up in every single brain she looked at, Dr Roberts sent a sample to a bacteriologist – who confirmed they were bacteria.
Tests on mice were then conducted to check whether it was possible for bacteria to be in their brain.
They found rodents bred not to have any traces of bacteria in their gut did not have any in their brains, either.
Dr Roberts and her colleagues aren’t sure how the bacteria got there, but suggest they travelled in the blood and became lodged in nerve fibres inside the skull.
Dr Teodor Postolache, from the University of Maryland, but who did not take part in the research, said: ‘There is much to investigate.’
‘I’m not very surprised that other things can live in the brain, but of course, it’s revolutionary if it’s so.’
If the research is found to be accurate, it could explain past studies which have found bacteria in the brains of people with Alzheimer’s disease.
The findings were presented at the annual meeting of the Society for Neuroscience.