Scientists at the Stanford University School of Medicine have been busy investigating how four Himalayan populations’ food intake affects their microbiome. Longtime residents of the foothills of the Himalayas live the Tharu, Raute, Raji and Chepang. They share similar culture, ancestry and language, but differ in their dietary lifestyles. The Tharu have done farming for the 250-300 years while the Chepang are hunter-gatherers. The Raute have only been practicing agriculture for the past 30 to 40 years. The research indicated that that the gut microbiome of the populations varied based on whether and how long it had changed from a hunter-gatherer lifestyle. 1
The lead author of the study, Aashisha Jha, a post-doctoral scholar at Stanford notes human microbiomes may be altered gradually as their lifestyles change and can occur throughout a human’s lifespan.
Previous research indicated big differences in the gut microbiomes of indigenous people of Africa and South America compared to those in industrialized Western populations of Europe and the US. This is the first research to show a difference in gut microbiome in related populations within a similar geographic area. 1
Our intestines house loads of bacteria that make up our gut microbiome. Roles of these bacteria include digesting food and regulating our immune systems. After birth, they immediately multiply and grow as soon as we begin to interact with our environment. Our consumption of breast milk, soft foods then solid fruits, vegetables and meats assists our guts in making a complex microbiome needed to maintain good health. 1
Our guts initially get exposed to wild foods in our environment. During the time of the Homo erectus about 1.8 million years ago, humans hunted and gathered fish, meat, seasonal nuts, seeds, roots, berries and vegetables. We transitioned to farming around 10,000 years ago which drastically changed our diets, cooking skills and lifestyles. 1
To see if this change in way of life impacted gut microbiomes, scientists collected stool samples from 56 people across the four Himalayan populations and from 10 in a control group of North Americans of European ancestry. Samples were collected over a two-month span. The researchers also collected individuals’ demographics, regular dietary practices, health status, drug use, alcohol and tobacco use and many other variables in the environment to evaluate the degree to which differences in lifestyle across the four Himalayan populations were associated with variations in their gut microbiomes. 1
An evaluation of the samples’ contents indicated four different types of gut microbiome. The differences showed the groups’ change from hunter-gatherers to farmers. As populations move away from hunter-gatherer lifestyle, subdivisions of bacteria such as Ruminobacter and Treponema that are plentiful in foraging groups such as the Chepang, decrease. 1
These bacteria are rare or totally absent in industrialized populations such as North America. Other strains of bacterial phyla like Actinobacteria and Verrocomicrobia, conversely are unlikely or non-existent in hunter-gatherers but show up as industrialization and farming become normalized.
As the Raute and The Raji have moved over to farming within the past 30 to 40 years, these data also reflect that big changes in human gut microbiomes can happen after decades of a population’s exit from a hunter-gatherer lifestyle.
Significant gut microbiome changes in a group of hunter-gatherers called the Hadza were seen in a study by Dr. Justin Sonnenburg, associate professor of microbiology and immunology at Stanford, published in Science magazine in 2017. Scientists identified that the Hadza’s gut bacteria was associated with the seasonality of foods they consumed. 2 Along with the current study, the results indicate how powerful diet is in altering gut microbiota.
Sonneburg notes that we have individual microbial identities and that this part of our makeup can be altered over short periods of time. Scientists are still studying which dietary factors as well as environment and lifestyle impact the transformation of bacteria. The have good evidence that drinking water and gut bacteria are related. This information will be valuable in future research to evaluate environmental impacts on gut health. 1
A more detailed survey is the next step and will focus on certain dietary components in the four Himalayan populations that are linked with alterations in the gut microbiome. 1
As the world rapidly urbanizes, our gut microbiomes change quickly, too. Jha feels this field of study is urgent because, “if we don't study the traditional societies today, 20 years down the road we may be too late."
Some tips for dietitians to pass on to their clients should follow recommendations based on the DASH and Mediterranean diets, which are well researched, plant-based diets.
- Eat a variety of whole grains such as steel cut oats, quinoa, farro, 100% whole grain breads and cereals for fiber and anti-oxidants.
- Include dried beans and lentils in your diet at least 3 times/week for soluble and insoluble fiber.
- Eat the peels and skins of fruits and vegetables for insoluble fiber.
- Include fermented foods such as yogurt, kefir, miso, sauerkraut and kimchi to maintain good bowel flora.
- Aashish R. Jha, Emily R. Davenport, Yoshina Gautam, Dinesh Bhandari, Sarmila Tandukar, Katharine M. Ng, Gabriela K. Fragiadakis, Susan Holmes, Guru Prasad Gautam, Jeff Leach, Jeevan Bahadur Sherchand, Carlos D. Bustamante, Justin L. Sonnenburg. Gut microbiome transition across a lifestyle gradient in Himalaya. PLOS Biology, 2018; 16 (11): e2005396 DOI: 1371/journal.pbio.2005396
- Smiths, S, Leach J, Sonneburg E., etc. al. Seasonal cycling in the gut microbiome of the Hadza hunter- Science 25 Aug 2017: Vol. 357, Issue 6353, pp. 802-806DOI: 10.1126/science.aan 4834
Submitted by Lisa Andrews, MED, RD, LD