The recovery from two Medieval toilets of around 500-year-old human excrement could reveal how dietary changes since the 15th century have triggered diseases.

Researchers led from Germany analysed deposits from two historic latrines that have been unearthed in Jerusalem, Israel and the Latvian capital, Riga.

Analysing gut bacteria from pre-industrial times could provide a vital baseline to help experts better understand the gastrointestinal health of modern populations.

There is a 'growing body of evidence' to suggest that changes in the microbiome have helped lead to diseases like inflammatory bowel disease, allergies, and obesity.

These shifts have been attributed to the 'trappings of industrialisation' — such as the advent of antibiotic treatments and the development of fast food.

'If we are to determine what constitutes a healthy microbiome for modern people, we should start looking at the microbiomes of our ancestors,' said paper author and biological anthropologist Piers Mitchell of the University of Cambridge.

These microbiomes can provide a baseline for comparison, he explained, as they belonged to people 'who lived before antibiotic use, fast food and the other trappings of industrialisation.'

In their study, Dr Mitchell and colleagues performed a microscopic analysis of sediment samples taken from the two medieval latrines in Riga and Jerusalem, both of which are thought to date back to between the 14th and 15th centuries.

To determine the kind of bacteria that would have been present in the digestive tracts of our European and Middle Eastern ancestors, the team had to distinguish these gut microbes in the sample from those normally found in soil.

The team identified evidence of a wide range of bacteria known to inhabit the guts of modern humans — including archaea, protozoa, parasitic worms and fungi.

The researchers compared the DNA of these organisms to those of the microbiomes of both present-day industrial and earlier hunter-gatherer populations.

'We found that the microbiome at Jerusalem and Riga had some common characteristics,' said paper author and archaeologist Susanna Sabin, formerly of the Max Planck Institute for the Science of Human History in Germany.

'They did show similarity to modern hunter gatherer microbiomes and modern industrial microbiomes — but were different enough that they formed their own unique group.'

'We don’t know of a modern source that harbours the microbial content we see here,' she explained.

'These latrines gave us much more representative information about the wider pre-industrial population of these regions than an individual faecal sample would have.' said Dr Mitchell.

'Combining evidence from light microscopy and ancient DNA analysis allows us to identify the amazing variety of organisms present in the intestines of our ancestors who lived centuries ago.'

Further studies will be needed at from other archaeological sites and time periods to fully understand how the human microbiome changed over time, the team said.

The full findings of the study were published in the journal Philosophical Transactions of the Royal Society B.