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

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.

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(CNN)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.
    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.
    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.
    The baobab fruit is the staple of the Hadza diet, packed with vitamins, fat in the seeds, and, of course, significant amounts of fibre. We were surrounded by baobab trees stretching in the distance as far as I could see. Baobab fruit have a hard coconut-like shell that cracks easily to reveal a chalky flesh around a large, fat-rich seed. The high levels of vitamin C provided an unexpected citrus tang.
    The Hadza mixed the chalky bits with water and whisked it vigorously for two to three minutes with a stick until it was a thick, milky porridge that was filtered -- somewhat -- into a mug for my breakfast. It was surprisingly pleasant and refreshing. As I wasn't sure what else I would be eating on my first day, I drank two mugs and suddenly felt very full.
    My next snacks were the wild berries on many of the trees surrounding the camp -- the commonest were small Kongorobi berries. These refreshing and slightly sweet berries have 20 times the fibre and polyphenols compared with cultivated berries -- powerful fuel for my gut microbiome. I had a late lunch of a few high-fibre tubers dug up with a sharp stick by the female foragers and tossed on the fire. These were more effort to eat - like tough, earthy celery. I didn't go for seconds or feel hungry, probably because of my high-fibre breakfast. No one seemed concerned about dinner.
    Hadza woman and child sitting at a fire, Lake Eyasi, Tanzania.