Ancient human feces shows how chronic modern diseases have been triggered by changes in diet, according to a recent study. The excrement was unearthed in three cave toilets and date back to around the time of Christ.
An analysis found it was deposited by people with much healthier gut bacteria than doctors see today. It could shed fresh light on gastrointestinal diseases, say scientists, and open the door to the development of better treatments.
“It may also lead to approaches to restore present-day gut microbiomes to their ancestral state,” says study corresponding author Dr. Aleksandar Kostic, of Joslin Diabetes Center, in a statement.
The international team mapped the genomes of 181 microbes from eight samples of excrement spanning 1,000 to 2,000 years ago. They were dug up at rock shelters in the southwestern U.S. and Mexico, with a third previously unknown. Comparing them to almost 800 current specimens also demonstrated they were more similar to non-industrialized microbiomes.
Altered gut bacteria has been linked to a host of illnesses ranging from allergies to diabetes, heart disease, cancer and even dementia. These shifts have been attributed to the “trappings of industrialization,” such as the advent of antibiotics and the birth of fast food.
“Loss of gut microbial diversity in industrial populations is associated with chronic diseases – underscoring the importance of studying our ancestral gut microbiome,” says Kostic. “However, relatively little is known about the composition of pre-industrial gut microbiomes.”
The study reports that the dramatic changes reflect differences between pre-industrial and modern diets. It also identifies an increase in antibiotic-resistance genes.
“An industrial lifestyle is linked to a lower diversity of the gut microbiome and an increase in the incidence of chronic illnesses – such as obesity and autoimmune diseases,” says Kostic. “However, our understanding of the evolution of the gut microbiome over time has been limited by a lack of data on pre-industrial gut microbes.”
The detailed genetic analysis of the well preserved human feces is the first of its kind. It found 61 of the genomes are previously not described, indicating the presence of species divergent from those seen in modern populations.
“The ancient and non-industrial samples include an enrichment of genes associated with the metabolism of starches,” explains Kostic. “This may be due to the higher consumption of complex carbohydrates compared with present-day industrial populations. Both the industrial and non-industrial modern-day samples are enriched in antibiotic-resistance genes relative to the ancient samples. These insights shed light on the evolutionary history of the human microbiome – and may aid in our understanding of the role of the microbiota in health and disease.”
The study appears in the journal Nature.
Report by South West News Service writer Mark Waghorn