New research is leading scientists to reconsider what bacteria in our belly may be good and bad for our health.

UNLV anthropologist Alyssa Crittenden led an international research team that for the first time studied the microbiome - the bacteria in our belly - of the Hadza, one of the few remaining human hunter-gatherers populations in the world. The results appeared in the April 15 issue of the journal Nature Communications.

Of note to researchers is that the Hadza are generally free from autoimmune and related diseases that plague industrialized nations. Studying how their diet - and their microbiota - differs from industrial populations can help scientists refine the importance of our body's bacteria to human health.

"We are starting to gain understanding of the species that inhabit our gut," said Crittenden, who has studied and lived among the Hadza for close to 10 years. "Studying hunter-gathers is important because they represent a small fraction of world's population who are living the way our ancestors lived."

The bacteria of the human digestive system have co-evolved with humans over millions of years and have the potential to help humans adapt to new environments and foods. Studies of the Hadza offer an especially rare opportunity to witness how humans survive by hunting and gathering, in the same environment and using similar foods as early humans did for most of our history.

Scientists compared fecal samples of the Hadza and urban Italians, who represent a post-industrialized population. Among the findings:

• The Hadza have a more diverse gut microbe ecosystem (more bacterial species) compared to the Italians. Less diversity has been tied to disease prevalence.
• "Good" bacteria bifidobacterium - common in all other humans and thought of as essential for maintaining health and nutrition - is missing from the Hadza diet.
• "Bad" bacteria treponema, certain types of which are linked with disease, are high in the healthy Hadza

Crittenden said the Hadza have been able to populate their guts with bacteria by adapting to their environment.

"The bugs in our gut are highly responsive to changes in our diet," Crittenden said. "These findings improve our understanding of how gut microbiomes may have helped early ancestors adapt and survive during prehistoric times."

The Hadza gut is well suited for processing indigestible fibers from a plant-rich diet, and likely helps the Hadza get more energy from the fibrous foods they consume.

"This study shows that we, as researchers, need to think about our environment and the way humans are hosting, taking care of and feeding these microbial species that have an impact on health," Crittenden said. "The human digestive system is adaptive and flexible and gut microbes have evolved with us."

The study is collaboration between researchers at UNLV, The Max-Planck Institute, The University of Bologna, Institute of Biomedical Technologies, University of Dar es Salaam and University of Cambridge.