Early human gut bacteria may have cycled with the season

first_img Email Sign up for our daily newsletter Get more great content like this delivered right to you! Country Microbes living in the guts of Tanzania’s Hadza hunter-gatherers change along with seasonal food sources. Matthieu Paley/National Geographic Creative You may be what you eat, but trillions of other lives depend on your diet: the microbes that live in your digestive tract. Scientists have long known that the foods we eat influence our intestinal microbiomes, but a new study finds that the gut residents of one of the world’s few remaining hunter-gatherer groups change seasonally, with different bacterial profiles in the dry and wet seasons. The findings—the first to show such a cyclical change in humans—may help researchers understand what our ancestors’ microbiomes were like before most of them switched to agriculture.Nearly 200 of the 1000 Hadza who live near Lake Eyasi in Tanzania’s Rift Valley practice a traditional hunter-gatherer lifestyle, eschewing agriculture in favor of hunting and foraging. In 2014, anthropologist Stephanie Schnorr and colleagues at the University of Oklahoma in Norman found that many of them harbored considerably more species of gut bacteria than people living in modern Western nations (a finding that dovetails with evidence that the Hadza don’t suffer from colon cancer, colitis, or Crohn’s disease). The Hadza’s gut bacteria also appeared to specialize in breaking down their fiber-rich diet.Unlike most people in industrialized nations, the Hadza eat seasonally: During the wet season, they forage for berries and eat honey, and during the dry season they hunt and eat game like warthogs, antelopes, and giraffes. They eat starchy tubers and baobob fruits year-round. By Michael PriceAug. 24, 2017 , 2:00 PMcenter_img To find out whether the Hadza microbiome also varies with the seasons, Jeff Leach, director of the Terlingua, Texas–based Human Food Project, and microbiologist Justin Sonnenburg of Stanford University in Palo Alto, California, and their colleagues got 188 Hadza people to collect their own stool samples in 2013 and 2014. “They simply went off into the bush, pooped, and dipped the swab immediately in the stool,” Leach wrote in an email to Science. To demonstrate how to do this without contaminating the samples, the researchers rolled wet clay which “made for hours of endless humor for the Hadza.”Back in his lab, Sonnenburg and colleagues analyzed the samples’ RNA and put together a list of which bacteria they contained. A stark pattern emerged: The Hadza people’s guts hosted a more diverse bacterial population during the dry season than the wet season. Bacteria from the Bacteroides genus were particularly abundant throughout the dry season; their numbers dropped off during the wet season, but returned to prominence with the next dry season. It’s the first evidence of seasonal cycling in the human microbiome, the researchers report today in Science.Looking more closely at the enzymes in the bacteria, Sonnenburg found that plant carbohydrate–digesting enzymes were more common during the dry season. That’s a bit of a mystery because the Hadza eat more meat and fewer plants that time of year, notes Alyssa Crittenden, an anthropologist at the University of Nevada in Las Vegas, who has studied the Hadza for 13 years. Crittenden and Schnorr note that the researchers don’t include detailed logs of what the Hadza participants were eating when they donated their stool samples. “Without dietary and behavior data to contextualize these data, this paper poses more questions than it answers,” Crittenden says. “I’m hungry for more data.”She agrees that the study sheds light on how the seasonal availability of plants and animals might have influenced the gut microbes of our ancient human ancestors, who would have hunted and gathered in a similar fashion to the Hadza. Knowing this could help researchers understand where ancestral humans lived and foraged, as well as which nutrients were available to them. It also suggests the human gut evolved a “biorhythm” in sync with natural food cycles, Schnorr adds, and that industrialized people’s microbiomes could be out of sync with that cycle. There are not yet enough data to determine how that affects our gut health, though, she says. But she stresses that the Hadza themselves don’t possess an “ancestral microbiome.” Evolutionarily speaking, they’re as modern as anyone else.Unfortunately, the window of opportunity to learn from the Hadza is closing, Crittenden says. Every year, more and more are leaving their small camps to work in nearby villages, and aid agencies active in the area are distributing nonnative foods like wheat flour and corn. “We’re running out of time … while this interview is happening, they are undergoing nutritional transition,” Crittenden says. “More data on their health, their biology, and their nutrition status will hopefully help change the types of [aid] programs put into place.” Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe Early human gut bacteria may have cycled with the season Click to view the privacy policy. Required fields are indicated by an asterisk (*)last_img

Leave a Reply

Your email address will not be published. Required fields are marked *