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Seasonal Variability in the Gut Microbiome of a Hunter-gatherer Population

Researchers have observed seasonal variability in the gut microbiome of a traditional hunter-gatherer population living in the African country of Tanzania, providing new insights into how diet and modernization may affect bacteria in the gut. The gut microbiome is the collection of all microbes present in the gut and/or their genetic material. It is known that people who eat a diet that is relatively low in fiber and high in fat and simple sugars, as is common in industrialized countries, have a less diverse gut bacterial community than people who eat a more traditional diet such as that of hunter-gatherers who forage for food. In other words, some bacterial groups in the gut microbiome of people eating traditional diets are missing in those consuming a more industrialized diet. A less diverse microbiome is associated with a variety of health conditions, such as obesity and inflammatory bowel disease, so exactly which bacterial groups are missing from industrialized societies and how microbiome diversity could be restored are intriguing questions for researchers.

In new research to help shed light on these questions, scientists studied microbiomes from people who eat a more traditional diet, the Hadza hunter-gatherers in Tanzania, and compared their microbiomes to microbiomes from people in other countries, including those in industrialized areas with a more modern diet. The Hadza’s traditional diet, which consists of food available in the wild, varies with local seasonal conditions. For example, berries and honey are more available during the wet season, and hunting (i.e., meat consumption) is more prevalent in the dry season. Researchers collected fecal samples from 188 Hadza people over a year. When the researchers compared the microbiome profile of the Hadza to 18 other populations across 16 countries, they confirmed previous research findings showing that gut microbial diversity relates to modernization: more traditional groups, like the Hadza, had the most diversity in their gut microbiomes. But the researchers uncovered an important clue when they looked at the Hadza’s gut microbiomes over different times throughout the year. They found that it differed in the wet and dry seasons, with some bacterial groups becoming undetectable in one season and then reappearing in another. In fact, when these bacterial groups disappeared seasonally, the Hadza microbiome profile was increasingly similar to those of people from industrialized countries. In other words, the bacterial groups that are most susceptible to the observed seasonal cycling in the Hadza are rare or absent in people living in industrialized countries.

These findings support the idea that the gut microbiome can fluctuate rather quickly with changes in diet. Also, a shift from a traditional diet to one more typical of industrialized populations could at least partially explain the loss of gut microbial diversity seen in modern societies. Further studies are needed to directly link these differences in gut microbial diversity to human health. However, understanding exactly what dietary changes could restore gut microbial diversity could help guide strategies to modify the gut microbiome for potential therapeutic purposes.

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