Researchers are hard at working trying to characterize the human gut microbiome, the community of microbes that live within the digestive tract of humans, mostly concentrated within the colon. A number of studies have begun to classify the microbes found in people of the Western world, and a few studies have even classified the microbes found in rural populations in Africa and South America.
In a recent study published in the journal Nature Communications, researchers analyzed the gut microbes of a traditional hunter-gatherer population—the Hadza, one of the last remaining hunter-gatherer communities in the world, situated in the Rift Valley ecosystem in northwestern Tanzania.1 The foraging and hunting lifestyle of the Hadza people is thought to most closely resemble that of Paleolithic humans. Because humans have relied on hunting and gathering for 95 percent of our history, understanding the gut microbial composition of communities such as these will help give us a better understanding from where our gut microbes evolved.
The Hadza people persist mostly on a diet of wild foods that include meat, honey, baobab, berries, and tubers. In the study, researchers compared the Hadza gut microbes to those of Italians, who consume a Western Mediterranean diet rich in plant foods, fresh fruit, pasta, bread, and olive oil, as well as small amounts of dairy, poultry, fish, and red meat. The diets of Italians are relatively low in fiber when compared to the Hadza diet, which is extremely high in fibers.
Stool samples from 27 Hadza, aged 8 to 70 years and 16 Italians aged 20 to 40 years were analyzed. “We report several findings that we feel support the conception of the microbiome as a diverse and responsive ecosystem adapting continuously as a commensal component of the host supra-organism,” noted the researchers, who interpreted the community of microbes as “an adaptation to the Hadza foraging lifestyle.”
They found characteristics consistent with a heavily plant-based diet, not surprisingly. Well-known fiber-degrading Firmicutes bacteria were present in both the Hadza and the Italians, while the Hadza were enriched in Prevotella, Treponema, and unclassified members of the Bateroidetes, Clostridiales, and Ruminococcaceae compared to the Italians. These bacteria are thought to provide the Hadza with fiber-degrading abilities that allow them to eat a diet so high in difficult-to-digest foods. The Hadza diet is an average of 70 percent plant based with seasonal variations depending on availability of meat.
The increase in Prevotella and decrease in Bacteroides they found is consistent with findings in other rural African groups.2,3,4 The difference between these populations and the Hadza, however, is the presence of grain-based foods in the diets of other Africans.
Interestingly, differences between male and female gut microbiota were found for the first time ever in studies of the human gut microbiota. These differences are thought to be due to the different lifestyle of men and women—men are the hunters while women are the foragers, and thus each eats a diet more in line with their food.
Also interesting, the presence of Treponema, a known pathogen in the Western world, does not pose an infectious threat in this population, reframing what we think of as a “healthy gut microbiome.” Truly, environment and lifestyle play a huge role on what microbes evolve with us. Treponema is known to have fibrinolytic capabilities that may be particularly beneficial to the women, note the researchers.
One unexpected finding of the study was a lack of Bifidobacteria among this group. The beneficial bacteria is associated with breastfeeding in infants and is usually high in number during infancy and present throughout adulthood in healthy populations. This is the first study to find a complete absence of Bifidobacteria and may be due to the different diet of the Hadza post weaning. Because the Hadza do not live with or eat domesticated animals or consume their milk, they may not come into contact with Bifidobacteria, the researchers postulate. They call for future studies that look at the gut microbes in Hadza infants to determine whether Bifidobacteria are entirely absent or only absent after infancy.
Gut microbial diversity was found to be higher in the Hadzu people than in the Italians, a finding that is consistent in studies comparing rural to Western civilizations as well as healthy to unhealthy populations. “Diversity and stability are factors with major health implications, particularly now that the human gastrointestinal tract is increasingly recognized as the gateway to pathogenic, metabolic, and immunologic diseases,” noted the scientists. Over one-third of the Hadza microbes were unidentified, so the researchers have their work cut out for them.
More studies will likely unfold from this and other rural populations, giving us a glimpse of our own microbes back in the hunter-gatherer days. Obviously, we are living in a different world today with different environmental and lifestyle needs, and so our microbes have adapted. As we continue to learn about what constitutes a healthy gut microbial composition in this day and age, we see that the answer is more complicated that we thought. Diversity seems to be the recurrent theme of a healthy gut microbiota, however. “Several diseases emerging in industrialized nations, like IBS, colorectal cancer, obesity, type II diabetes, Crohn’s disease, and others, are significantly associated with a reduction in gut microbial diversity,” said Stephanie Schorr, lead researcher.
References
- Schnorr SL, Candela M, Rampelli S, et al., “Gut microbiome of the Hadza hunter-gatherers.” Nat Commun. 2014 Apr 15; 5, Article number: 3654.
- DeFilippo C, Cavalieri D, DiPaloma M, et al., “Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa.” Proc Natl Acad Sci U S A. 2010 Aug 17;107(33):14691-6.
- Yatsunenko T, Rey FE, Manary MJ, et al., “Human gut microbiome viewed across age and geography.” Nature. 2012 May 9;486(7402):222-7.
- Ou J, Carbonero F, Zoetendal EG, et al., “Diet, microbiota, and microbial metabolites in colon cancer risk in rural Africans and African Americans.” Am J Clin Nutr. 2013 Jul;98(1):111-20.