What a hunter-gatherer diet does to the body in just three days

Editor’s Note: Tim Spector is professor of genetic epidemiology at King’s College London. The views expressed in this commentary are solely those of the writer. CNN is showcasing the work of The Conversation, a collaboration between journalists and academics to provide news analysis and commentary. The content is produced solely by The Conversation.

Mounting evidence suggests that the richer and more diverse the community of microbes in your gut the lower your risk of disease. Diet is key to maintaining diversity and was strikingly demonstrated when an undergrad student went on a McDonald’s diet for ten days and after just four days experienced a significant drop in the number of beneficial microbes.

Similar results have been demonstrated in a number of larger human and animal studies.

Fast food vs. the African diet: The bacteria battle waged in your gut

Your gut microbiome is a vast community of trillions of bacteria that has a major influence on your metabolism, immune system and mood. These bacteria and fungi inhabit every nook and cranny of your gastrointestinal tract, with most of this 1kg to 2kg “microbe organ” sited in your colon (the main bit of your large intestine).

We tend to see the biggest diet-related shifts in microbes in people who are unhealthy with a low-diversity unstable microbiome. What we didn’t know is whether a healthy stable gut microbiome could be improved in just a few days. The chance to test this in an unusual way came when my colleague Jeff Leach invited me on a field trip to Tanzania, where he has been living and working among the Hadza, one of the last remaining hunter-gatherer groups in all of Africa.

A Hadza man hunting with bow and arrow, Lake Eyasi, Tanzania.

My microbiome is pretty healthy nowadays and, among the first hundred samples we tested as part of the MapMyGut project, I had the best gut diversity – our best overall measure of gut health, reflecting the number and richness of different species. High diversity is associated with a low risk of obesity and many diseases. The Hadza have a diversity that is one of the richest on the planet.

The research plan was devised by Jeff who suggested I should have an intensive three days of eating like a hunter gatherer during my stay at his research camp. I would measure my gut microbes before heading to Tanzania, during my stay with the Hadza, and after my return to the UK. I was also not allowed to wash or use alcohol swabs and I was expected to hunt and forage with the Hadza as much as possible – including coming in contact with the odd Hadza baby and baboon poo lying about.

'Lost' early photographs shed light on Sudan's Nuba and Latuka tribes

To help us record the trip I was accompanied by Dan Saladino, the intrepid presenter and producer of BBC Radio 4’s The Food Programme, who was preparing a Hadza microbe special.

After a long tiring flight to Mount Kilimanjaro Airport in Tanzania, we stayed overnight in Arusha, a city in the north of the country. Before setting off the next morning, I produced my baseline poo sample.

After an eight-hour journey in a Land Rover over bumpy tracks, we arrived. Jeff beckoned us to the top of a huge rock to witness the most amazing sunset over Lake Eyasi. Here, within a stones throw of the famous fossil site of Olduvai Gorge and with the stunning plains of the Serengeti in the distance, Jeff explained that we were never going to be closer to home as a member of the genus Homo, than where we were standing at that moment.

The million-year-old diet

The Hadza seek out the same animals and plants that humans have hunted and gathered for millions of years. Importantly, the human-microbe tango that played out here for aeons probably shaped aspects of our immune system and made us who we are today. The significance of being in Hadza-land was not lost on me.

Unlike the Hadza, who sleep around the fire or in grass huts, I was given a tent and told to zip it up tight as there were scorpions and snakes about. I had to be careful where I stepped if I needed a nocturnal pee. After an interesting but restless night’s sleep, a large pile of baobab pods had been collected for my breakfast.

Wodaabe, Gerewol —

At the end of the rainy season near Lake Chad, northern Niger, Wodaabe people come together for Cure Salee, the "Festival of Nomads." At the center of celebrations is Gerewol, a male beauty contest and courtship ritual. Young men -- traditionally herdsmen -- wear full makeup, jewelry and their finest clothes and stand in line to await inspection by female onlookers. White teeth and white eyes are highly prized, so participants will grin broadly and pull all manner of expressions in the hope of attracting attention. It's flirtation en masse, in the hope of winning a night of passion with one of the judges.

Mursi, lip plates —

Circular lip plates called dhebi a tugion are worn by some Mursi women near Jinka in Ethiopia's Omo Valley. They are one of the few tribes that continue the practice in East Africa, but archaeologists have discovered lip plates in the region stretching back 30,000 years, says anthropologist Dr Jerome Lewis of University College London. "It's a body modification that people find beautiful," he says. "It's also very striking and a distinctive way of marking your difference from other people around you."

The bottom lip is pierced with a wooden peg inserted, which is replaced with larger pegs thereafter. Once the hole is big enough the first of a succession of ornamental ceramic saucers are inserted, stretching it over a period of years -- one example from the neighboring Surma tribe measured 19.5cm wide.

Himba, otjize —

Women of the semi-nomadic Himba tribe in northern Namibia are famous for their reddish hair and complexion. It's the result of otjize, a paste of butter, fat and red ocher, applied daily to their hair and skin. It was once speculated that the otjize served as a form of sun protection and to ward off insects, however the women say it's purely for aesthetic reasons -- which makes sense, given that Himba men don't take part in the practice.

Hamar, bull jumping —

Herdsmen become hurdlers in the Omo Valley, Ethiopia. Young men of the Hamar tribe, one of many in the valley, prove their manhood by jumping on prize bulls and then running across their backs -- all while naked. The purpose? It's a coming of age ceremony, and only when the participant has traversed the bull run four times will he be allowed to marry. Slip and you risk a hard fall: "Because it's a manhood initiation ritual, [failure] is likely to affect the perception of someone's manhood and that of course can have all sorts of dire consequence," adds Dr Lewis.

Xhosa, Ulwaluko —

In Eastern Cape, South Africa, young Xhosa men take part in a coming of age initiation called Ulwaluko. The youths, known as abakhwetha, are first circumcised without anesthetic, before being sent away from their village and into the bush, with minimal supplies and wrapped in a blanket. Wearing white clay on their faces, initiates will fend for themselves for up to two months, living in a structure built by the village's adult community specifically for Ulwaluko. Upon their return they are no longer referred to as "boy" and receive a new blanket. The initiation has not been without its criticisms, due to complications and malpractice surrounding the circumcision process.

Chewa, matriarchy —

Women of the Chewa tribe may not be quite on equal footing as men, but they do hold the key to one thing: inheritance. Descent and succession for the Bantu-speaking tribe, spread across Zambia, Zimbabwe, Malawi and Mozambique, is matrilineal, with property and land inherited from their mothers. "Although inheritance passes down the female line, which definitely gives women more power in society, it's still male-dominated and patriarchal in the sense that men are still at the apex of power," explains Lewis. "People have an assumption that matrilineal societies are somehow favorable to women -- and they are certainly more favorable than some of the extreme patrilineal societies -- but they're not societies that give women equal power."

One thing Chewa women are shut out of is the Nyau brotherhood (pictured), a secretive society who can channel spirits and performs a ritual dance called Gule Wamkulu around harvest and at weddings and funeral.

Maasai, spitting —

Spittle is an essential part of life for the Maasai of East Africa, as it acts as a blessing. "People have different views about where the power and essence of somebody resides," explains Lewis. For some, "spit represents an essence of you as a person."

To spit is "a way of blessing people by giving something of yourself; your own power to someone else." It starts at an early age, when newborn babies are spat on to wish them a good life. "If you leave a place, elders will come and spit on your head in order to bless your departure, and that whatever you do you're safe and kept well," adds Lewis.

San, healing dance —

The San of South Africa, Botswana, Angola and Namibia are, according to some researchers, the world's oldest people. Their hunter-gatherer culture stretches back tens of thousands of years, and integral to it is the trance dance, also known as the healing dance. Historically an all-night affair, the practice brings the whole community together, led by healers and elders dancing around a fire, chanting and breathing deeply until they induce a trance state. It offers the chance to commune with ancestral spirits of the departed and for healers, cure sickness within other dancers.

Lewis says that this tradition is under threat: "In some places in southern Africa the San now perform their traditional culture exclusively for tourists, because they've been forced out of all their territories as hunter-gatherers by conservationist organizations. This means that by extension... these performances are not the original initiations but a facsimile of them."