The gut microbiome-crucial in modulating the health of the immune, metabolic and neurological systems-is subject to dramatic rarefaction in the ‘modern’ lifestyle that relies on an ‘agro-industrial’ diet. Researchers at Stanford University (Carter et al., 2023) collected and compared the bacterial composition of 351 fecal samples from Hadza hunter-gatherers from Tanzania and as many from Nepal and California. (1)
The rarefaction of the gut microbiome
The Hadza, about 1,300 people, are one of the last remaining hunter-gatherer tribes in Africa. They reside near Lake Eyasi in Tanzania’s central Rift Valley and are threatened by the erosion of their territory that has been denatured by agricultural settlements, documents Survival, a volunteer organization for indigenous people. (2)
They live in camps in the bush in groups of about 5-30 individuals. They move from camp to camp about every 4 months, drink mainly from water sources and streams, and eat a diet that includes tubers, berries, honey, and wild animals. Genetically, they are considered one of the oldest lineages of humankind.
124 bacterial species lost in ‘industrialized’ population
The researchers collected and analyzed stool samples collected from 167 Hadza individuals (including 30 infants and 6 mothers) between September 2013 and August 2014.
Ultra-deep metagenomic sequencing of the samples recovered 91,662 genomes of bacteria, archaea (archaebacteria), bacteriophages and eukaryotes, 44% of which are absent from existing unified datasets.
The research identified 124 gut-resident bacterial species absent in industrialized populations. Indeed, in the latter, the evolution of the gut microbiome involves a rarefaction of bacterial diversity and the presence of genes associated with oxidative stress, probably due to the adaptation of the microbiome to inflammatory processes.
Microbial poverty in the West
Among the causes of this transformation, researchers mention typical aspects of the Western lifestyle:
– consumption of highly processed foods,
– High rates of antibiotic administration,
– Delivery by cesarean section and use of artificial milk,
– hygiene of the living environment and
– Reduced physical contact with animals and soil.
A rarefaction of the microbiome is, moreover, also observed in immigrants to the United States of America, which gradually becomes characterized by an industrialized, less diverse microbiome.
Hadza, a surprising bacterial strain
To compare the Hadza microbiome, the researchers performed additional deep metagenomic sequencing on fecal samples from Nepalese and California individuals.
The Nepalese samples come from four distinct populations in gatherers (Chepang) and agrarians (Raute and Raji, recent agrarians, and Tharu, long-standing agrarians).
The results show as many as 730 bacterial species in the gut microbiome of the average Hadza adult, compared with 277 species in the California gut microbiome of the average adult, 317 species of Nepalese pickers and 436 species of Nepalese agrarians.
The research enriches gut-associated genome databases with new information and provides a benchmark for studying the impact of Western lifestyle on the gut microbiome. Organic food, as it turns out, is the only salvation today to safeguard our microbiota.
Marta Strinati
Notes
(1) Matthew M. Carter, Matthew R. Olm, Bryan D. Merrill, Dylan Dahan, Surya Tripathi, Sean P. Spencer, Feiqiao B. Yu, Sunit Jain, Norma Neff, Aashish R. Jha, Erica D. Sonnenburg, Justin L. Sonnenburg. Ultra-deep sequencing of Hadza hunter-gatherers recovers vanishing gut microbes. Cell. 2023 June 21, DOI:https://doi.org/10.1016/j.cell.2023.05.046
(2) The Hadza. Survival. https://www. survival.it/galleria/hadza
Professional journalist since January 1995, he has worked for newspapers (Il Messaggero, Paese Sera, La Stampa) and periodicals (NumeroUno, Il Salvagente). She is the author of journalistic surveys on food, she has published the book "Reading labels to know what we eat".
