Please Pass the Microbes

A few days ago I accompanied two Hadza hunters to a series of seeps or springs where they had set up hunting blinds of tall grass to ambush thirsty animals. It’s late dry season in Tanzania and dwindling water sources force otherwise dispersed animals to aggregate, and if you’re a hunter-gatherer, this is a good thing. The week before a hunter killed a zebra from one of these blinds with a poison tipped arrow (a windfall of >400-500 pounds of protein and fat that would be consumed in <72 hours!). On our way back to camp, we came across another Hadza that had moments before killed an adult Impala. After helping hoist the deceased into a low hanging tree – to hang by its head for field dressing – I then witnessed something that up until that point I had not fully appreciated the significance of in the co-evolution of humans and our microbes and its potentially profound implications for our health in the so-called modern world.

IMG_3039I had come to Tanzania as part of a collaboration of US, Canadian, and Tanzanian researchers to try and understand what the gut microbiome might look like in a group that still hunts and forage’s 95-100% of its food and more interestingly, how pronounced seasonal changes in resources – between wet and dry seasons – might impact compositional and functional changes in the microbiota. One pressing question in microbiome research – at least what the public and many public health officials wants to know (not to mention food manufacturers and Big Pharma) – is there an optimal composition of gut microbes we should strive for, and at what age, and what diet and lifestyle choices will get us to this microbial fountain of health. Which is, of course, a complex question.

The Hadza may provide some interesting insight into this question as they live in a part of Africa that presumably gave rise to our genus (Homo) and our more distant tree-hugging ancestors. The Hadza still hunt and forage many of the animals and plants that our ancestors relied upon, are covered in the same soil, drink the same water, and follow more or less a seasonal hunter-gatherer lifestyle that dominated the last two million plus years of human evolution. While its important to understand how humans lived once they left Africa and settled other parts of the planet in the last ~60,000 years, the huge spans of time our kind spent in Africa evolving towards the lion’s share of our current physiology (and current adaptive immunity), is potentially more interesting when it comes to understanding the human-microbe relationship – both good and bad.

Importantly, the Hadza don’t keep livestock or plant foods of any kind, and have limited access to modern medications like antibiotics (at least the more remote Hadza camps that we are studying). While some may argue that the Hadza are not perfect referents for the way it once was, it depends on the questions you are asking. For our purposes, studying how humans acquire microbes from birth throughout life (from others and the larger meta community of microbes in nature) in a group where babies are all still born naturally (no c-sections), are breastfed on average for 2+ years, where children still sleep with their mothers years beyond weaning, take no antibiotics, don’t drink water that has been treated with chlorine and fluoride, where multiple generations stay together (not separating the seniors into assisted living facilities), don’t eat processed foods, and newborns to the eldest in the community are still covered in nature’s blanket of everything that comes from living outside 24/7 and interacting in an intimate way with 100s of species of plants and animals.

Back to the Impala.

Before the two Hadza men I was with jumped in to help skin and gut the Impala, I quickly took swabs of each of their hands (and 1 hour after, 3 hours after, and so on) to assess how the skin (palm) microbiota change throughout the day/week of a typical Hadza (We’ve sampled the hands [and stools] of 150+ Hadza men, women, and children so far). As they slowly and methodically dismembered the animal, they carefully placed the stomach and its still steaming contents on the fleshy side of the recently removed hide. In a separate area, they piled the fatty internal organs (which men are only allowed to eat by the way). Once the animal had been processed more or less, I was amazed to see all three men take a handful of the partially digested plant material from the recently removed stomach to scrub off the copious amounts of blood that now covered their hands and foreman’s. This was followed by a final “cleaning” with dry grass for good measure.

Hadza hand sanitizer - stomach contents from Impala.
Hadza hand sanitizer – stomach contents from Impala.

While I was fascinated by the microbe-laden stomach contents being used as hand scrubber – presumably transferring an extraordinary diversity of microbes from the Impala gut to the hands of the Hadza – I was not prepared for what they did next. Once they had cleaned out – by hand – the contents of the stomach (“cleaned” is a generous word), they carved pieces of the stomach into bite-sized chunks and consumed it sushi-style. By which I mean they didn’t cook it or attempt to kill or eliminate the microbes from the gut of the Impala in anyway. And if this unprecedented transfer of microbes from the skin, blood, and stomach of another mammal wasn’t enough, they then turned their attention to the colon of the Impala.

After removing the poo pellets (which we collect samples of as well), they tossed the tubular colon onto a hastily built fire. However, it only sat on the fire for a minute at best and clearly not long enough to terminate the menagerie of invisible microbes clinging to the inside wall of the colon. They proceeded to cut the colon into chunks and to eat more or less raw. For myself, I kindly turned down offers to taste either the raw stomach or the partially cooked colon – but did eat some tasty Impala ribs I thoroughly turned on a stick over the fire to a microbial-free state of well done.

The Hadza explained that this is what they always do, and have always done (though I suspect sushi-style eating of innards is not an every-kill ritual. But….). Whether it’s an Impala, Dik Dik, Zebra, bush pig, Kudu or any other of the myriad of mammals they hunt and eat, becoming one with the deceased’s microbes in any number of ways is common place – same goes for 700 plus species of birds they hunt (minus abundant amounts of stomach contents for hand sanitizer!). While less obvious than at the “kill site,” the transfer of microbes continued back in camp when women, children and other men handled the newly arrived raw meat, internal organs, and skin. The transfer continued as the hunters engaged (touching) other members of the camp.

The breathtaking exchange (horizontal transfer) of microbes between the Hadza and their environment is more or less how it’s been for eons until humans started walling ourselves off from the microbial world through the many facets of globalization. Rather than think of ourselves as isolated islands of microbes, the Hadza teach us that we are better thought of as an archipelago of islands, once seamlessly connected to one another and to a larger metacommunity of microbes via a microbial super highway that runs through the gut and skin/feathers of every animal and water source on the landscape (for those of you keeping up with your homework, this is Macroecology 101). The same can be said for plants and their extraordinary diversity of microbes above (phyllosphere) and below ground (rhizosphere) that the Hadza, and once all humans, interacted with on a nearly continuous basis.

The Hygiene Hypothesis – or Old Friends Hypothesis, if you prefer – posits that a great many diseases (specifically autoimmune diseases) result from a disconnect with the natural world and its myriad of microscopic life. Microbes and other tiny things that once trained our immune system to distinguish between friend or foe and even Self. Our children are no longer born in the microbe-rich dirt, but rather hyper-sterile rooms where even the air is scrubbed with mechanical systems. Further, an increasing number of our kids are born through an incision rather than the microbial-rich birth canal and the percentage that are still consuming microbial-rich milk from mom at 2 or even 1 year of age can be counted in the low single digits depending on where you live and your lot in life. Our kids – most of them, or adults for that matter – have no interaction with extensive microbial networks that the Hadza and our ancestors once experienced. For us, the microbial super highway that once connected all humans to the larger metacommunity of microbes now dead ends at closed windows in a home at the end of the street with very few species of plants in the yard and no or few animals – save a dog or two – and a wet wipe and anti microbial something or other at every turn.

All samples are frozen in the field in liquid nitrogen.

There is no arguing that our modern lifestyle and wonders of modern hygiene, sanitation, and medicine have saved a great many lives over previous generations – especially among the youngest in our ranks who are especially vulnerable to diarrheal and respiratory disease (which is still a problem in densely crowded conditions in many developing countries). But as we tout the triumph of modern life span over the more cruel life of the days of yore, we need to keep in mind that our point of reference is the filth and pestilence of the crowded towns and cities of the last millennia or so – not the nomadic lifestyle that dominated 99% of human/hominin evolution before we plowed the ground and pinned select animals. Yes, ~20% of Hadza children die young, but those that survive to adulthood have a good chance to live into their 60s, 70s, and 80s. To suggest that we can’t learn about the very foundations of human-microbe mutualism, commensalism, vertical/horizontal transmission, and microbial succession across an age gradient in a society unencumbered by the confounders of so-called modern life because of childhood mortality rates seen as extreme by modern medical standards, is to throw the baby out with the bath water. The Hadza, and the very limited number of groups like them, are disappearing fast – and this potential microbial Noah’s Ark will soon be lost.

What we might learn from the Hadza’s intimate participation in the microbial super highway of the natural world is made more interesting when you consider a series of experiments recently published in the prestigious journal Science. In an elegant set of experiments, the researchers took poo samples from several sets of twins discordant for obesity and inserted them into germ free mice. In other words, one of the twins was lean while the other a little chunky. As with previous experiments, the transplanting poo from obese twin made the recipient mice obese and the poo from the lean twin resulted in lean mice – demonstrating that host phenotype (obese or lean) is transmissible. I admittedly just glossed over a very detailed study with lots of interesting moving parts – if you have access to this journal, I would highly recommend reading the entire paper. That said, one aspect of the study is worth drawing additional attention – and also happens to be the part of the multi-faceted study that received the most attention from the media.

After taking germ free mice and inoculating them with either the microbiota from the lean or chunky twin – and thus making the bugged mice fat or lean – they then stuck the lean and fat mice together in the same cage and fed them the same diet. Since mice are coprophagic – ie, they eat poo – the researchers were curious to see what happened. Throughout the cohousing of lean and obese mice, the researchers collected fecal samples (careful to keep separate which pellets came from which mouse) every day more or less for a few weeks. They also monitored body composition as well.

Remarkably, analysis of fresh poo pellets from the mice revealed that several species of bacteria from the lean mice successfully invaded the gut of the fat mice, but not the other way around (remember, the mice were eating each others poo and thus each others microbes). In other words, the gut microbiota of the fat mice reconfigured to look more similar to the lean mice – yet, as mentioned, the lean mice microbiota remained stable and did not uptake any bacteria from the obese mice despite eating the fat mice poo. Furthermore, the invasion of species from the lean mice into the obese mice essentially shut down further weight gain in the obese mice. Interestingly, the diet was low fat, high plant polysaccharide and fed ad libitum (all you can eat).

Using a snazzy piece of analytical wizardry, the researchers were able track exactly which species successfully invaded the gut of the obese mice from eating the poo of the lean mice. Of the handful of species that invaded the gut of the obese mice from the lean cage mates, Bacteroides spp. from the phylum Bacteroidetes were largely responsible in protecting against increased adiposity in the fat mice.

A new coffee-table-like book about our work in Africa will be available soon. Click here ( is you want to receive an e-mail when the book is available. 100% of the proceeds go to the research.
A new coffee-table-like book about our work in Africa will be available soon. Click here if you want to receive an e-mail when the book is available. 100% of the proceeds go to the research.

Since it appeared that various Bacteroides spp. were not only successful invaders but also conferred some kind of leanness, the researchers cooked up a cocktail of a number of Bacteroides spp. and a handful of others (39 species in all) and did the experiment all over again. This time, they put obese mice in a cage – made obese from the chunky twins microbiota – and cohoused them with originally germ free mice that received only the cocktail of 39 species. This time around, the lean mice poo of the 39 specific species was unable to protect the obese mice from getting chunkier. This experiment demonstrated that its not one strain or handful of strains that confer less adiposity and more leanness in obese mice, but more complex interactions underlie the protection against adiposity.

In one final experiment, they put mice inoculated with the full microbiota from a lean or obese human twin and stuck them in the same cage – same as before. However, this time they changed the diet to high saturated fat, low fruit and vegetable – that is, low fiber. Like the previous experiment, the mice consumed one another’s poo but this time around, bacteria from the lean mice didn’t successfully invade the gut of the obese mice. This suggest the underlying mechanism for protection from obesity in this particular experiment is more complex, possibly involving a great many more community members then just a handful of species and diet dependent.

In the context of the experiments discussed in the Science paper, I can’t help but think that us “moderns” moving through our squeaky clean lives – obsessing over every bite of food we eat – might be suffering oh so slightly from a detour or full blown exit from the microbial super highway that once dominated so much of our evolutionary history. Though the Hadza and presumably our ancestors didn’t directly consume each other feces or that of the animals on the landscape in a deliberate way on a frequent basis, clearly our hunter-gatherer ancestors had a more intimate involvement in the total microbial metacommunity of the environments they inhabited than we do in the concrete jungles we call home.

It’s tantalizing to think that as part of this microbial web, that our ancestors didn’t benefit in some way with the nearly daily sampling and exchange of microbes with animals as diverse as zebra, impala, birds, or even carnivores like lions (which the Hadza eat by the way), or from a dizzying number of plants sprouting from soil teeming with bacteria (and their genes) worth sampling and possibly utilizing for our mutual benefit. Not only is this plausible, it’s highly likely.

**A tiny, tiny version of this blog post appeared in Nature.


124 Comments Add yours

  1. Brad P says:

    @Jeff – this is super interesting and such an exciting ray of hope for the better health of modern mankind. I’m chucking at the inevitable cottage industry that may sprout of wealthy city dwellers paying handsome sums for fecal transplants from Hadza donors. The truth is sometimes stranger than fiction. Enjoy that raw colon, bro!

    1. Jeff Leach says:

      Too funny. In January I’m going “full hunter-gatherer” to see if I can shift my US microbiome to an ancestral/Hadza composition – will be interesting… But i’m pretty sure colon will not be on my menu!

      1. silverdelrio says:

        Wow! That is so inspiring! What an amazing article, do you have a follow up to your hunter-gatherer period? As I am seeing this, the post is over 2 years old. 😀

        1. david says:

          it’s now 2018, and still inspiring.

  2. Ann says:

    This was a bracing read for the first thing in the morning. Fascinating! I’m wondering about the Hadza’s general health. Do they seem healthy by the developing world’s standards? The lack of hand washing is very interesting to me. Seems like there would be a lot of gastrointestinal distress…

    1. Jeff Leach says:

      Yeah – you would think… But from what I can tell, not too many runny stools – but does occur. Something I didn’t talk about – which may be important – is that the greater microbial diversity they likely carry may be protective at some level – ie, diverse ecosystems are more resilient.

      1. Avishek says:

        20% infant mortality, from infectious diseases that vaccines could prevent?

        Also that March 2014 paper on the Hadza said that some women developed a type of treponema, as these bacteria are opportunistic pathogens. So I’d like to see this topic explored further.

        Very neat details about the spread of bacteria from the stomach of the animals, wonder how often that happens during the year and if it’s possible to trace the spread of these bacteria from the men who hunted to the rest of the Hadza population, and if there are any health effects.

  3. cathydenise says:

    Do Hadza seniors who live to (relative) old age (70-80) develop any kind of dementia that you are aware of?

    1. Jeff Leach says:

      good Q. not aware of any data which suggests so…. but…

  4. Steve says:

    Fascinating! So very fascinating! Thank you for your work and writing about it.

  5. dbfact says:

    Great stuff. Given this complexity, I’m wondering if you personally consume probiotic supplements. Larry Smarr has said that only 15% of our gut bacteria are aerobes, so the other 85% cannot be impacted by the supplements (I think he did recommend prebiotic foods, tho). I am not yet clear on this: is it only ‘good’ bacteria that feast on the pre-biotics?
    Also, am curious why you passed on the stomach – fear of food born illness in the middle of nowhere?

    1. Jeff Leach says:

      Good questions. In short, I think probiotics r great if you think they are. However, you might better off eating more whole plants and saving your money. The gut ecosystem is vast, diverse, and ebbs in and out of resilience depending on your health state, diet and lifestyle. Eating a greater diversity of plants should help “most” guts – but note this doesn’t mean meat is out – just that eating whole plants is important. Prebiotics – like FOS, GOS etc – by definition should only stimulate the growth of known beneficial bacteria – think bifidobacterium. But depending on the gene make up of any given microbe, any number of members can utilize specific prebiotics…. As for passing on the stomach, I doubt I had enough diversity in my own to fend off the myriad of exotic bugs clinging to the walls of the impala stomach. Maybe in a few months after I have spent more time on the ground “acquiring” some east African bugs!

      1. dbfact says:

        Thanks for your prompt reply. HG project only $99 now (I’m so excited – will order shortly)! Also, if you foresee any role for volunteers for next trip, I am likely in a position to do so. I’m just switching over to Chrome from Safari (and just starting on WP) so not clear if you can access my email. I can give you more information about my background if interested. Thanks again, Debbie

        1. Jeff Leach says:

          Thx. sure, shoot me your info at jeff AT human food project DOT com…..

  6. ayelet says:

    Such an interesting entry! Looking forward to reading more of your experience, especially your full hunter-gatherer trial. Remember- no hand washing 🙂

    1. Jeff Leach says:

      No hand washing. Check!

  7. Ben says:

    It’s horrifying to think that someday, the work you’re doing will be looked back upon as part of a long-lost, ‘fundamental’ aspect in the robustness of human evolution that we’ve slowly destroyed in our self-centric pursuits of ‘health’…

    But at the same time, to think I’m sitting here reading about it in a blog post? So cool!

  8. Nancy says:

    Fascinating info! I teach “wild” fermentation workshops to help individuals reclaim this important community of probiotics that occur naturally when raw veggies are cut up and covered with water or salt and water. I talk a lot about gut microbiota and the importance it has on the immune system. I’m not sure I’ll pass on the info about colon and stomach eating; however I will talk about the complexity of communities established in our own guts.

  9. Keith Bell says:

    One of the best pieces I’ve ever read on the subject, Jeff. And good luck come January’s flora shift! But the Hygiene Hypothesis has one major flaw, the assumption modern sanitation is a good thing without understanding the end result of the activated sludge process which is only 100 years old. Like mice, humans are consuming one another’s waste as sewage effluent pollutes drinking water and sewage biosolids are farm land applied. We’re also mixing this waste with livestock waste allowing horizontal gene transfer, thereby creating antibiotic resistant superbugs. This melding of microbial existence you so eloquently describe is no excuse to defecate in water.

    1. Cate says:

      The Humanure Handbook..? Brilliant book on this subject…

  10. This was a fascinating read! Your research on these hunter/gatherer groups is so important to our understanding of how it really was. These details (the stomach and intestine eating) may have been lost forever if not for your documentation. I am certain pharmaceutical companies will jump on this potential cold mine in obesity research and look to develop a “skinny pill” made of particular strains of bacteria! Look forward to your book and further reports!

  11. AnneS says:

    “those that survive to adulthood have a good chance to live into their 60s, 70s, and 80s”
    And I bet they live without all the chronic diseases that we live with here – rampant allergies, autoimmunity, allergies, austism, alzheimers, arthritis, and that’s just some of the A’s. Colitis and Crohns and IBS are rampant here now too.

  12. AnneS says:

    oops, I wrote allergies twice – I mean asthma

  13. David says:

    Jeff, Please explain to me how ingesting the specialized gut biota of freshly killed African ruminants ( presumably optimized to breaking down cellulosics and complex carbohydrates found in African grass) will somehow influence the gut biota of a meat eater? Those are two completely different substrates for these bacterial populations and likely not at all compatible. Your PCR data may show little correlation between the two populations. Perhaps the hand washing is to take advantage of gut and bacterial surfactants plus chlorophyl pigments to remove fats, blood stains and strong odors associated with the breaking down and butchery of the animal carcass?

    1. Jeff Leach says:

      Yes, humans are meat eaters – but we are omnivores. The human microbiota is endowed with millions of genes that not only specialize in amino acid metabolism, but carbs and a dizzying # of other things as well. Note the Hadza get ~75% of their calories from plants – they eat tons of fiber. Note meat “supplements” the plant diet not the other way around. The point of the microbial super highway analogy is that the human microbiome samples new bacteria as they pass through – both whole bacteria and their genes – and its the continuous supply (horizontal transfer) that likely creates an extraordinary diversity of bacteria that help make the Hadza gut more resilient to perturbations. But we have a long way to go and a lot to learn. Keep the good Qs coming.

  14. I have to wonder if the stomach contents doesn’t actually work as a sort of hand sanitizer. After all, the acid in our own stomachs is supposed to kill bacteria that make their way there before they can wreak havoc on our systems. Then the eating of the stomach is another puzzler. Maybe it’s the hunter-gatherer equivalent of our own betaine HCl supplements?

    1. Jeff Leach says:

      Good point. The sampling will help us know. But in short, the Impala gut is full of bacteria….

  15. Rachael says:

    I thought you might be interested to know that in an old James Beard cookbook I own there is a recipe for song birds which suggests roasting them over a slice of toast so that when the trace falls you can eat that too. (The entrails.)

  16. Wendy says:

    @Jeff, this reading was fascinating. I have many questions regarding their plant intake and type of preparation. Also, which are the first foods they introduce to babies and finally why women are not allow to eat organs. Thank you for this amazing work.

    1. Jeff Leach says:

      Great Q. I will be writing a few posts over the coming weeks about this. The primary weaning food is Baobab fruit. An amazing fruit high in vit C, tons of fiber and lots of fat (in the seed/kernel). In short, starting around age 6 mo, kids will consume 30-100g/day of dietary fiber… More on this in a later post.

  17. Francesco says:

    Very interesting report! It makes me laugh that many people I know think I’m crazy when I tell them that I prepare lactofermented foods like those I learned from Fallon’s “Nourishing traditions” and Katz’ s “Wild fermentation”. They should learn that bacteria are not as bad as we’ve been taught to believe.

  18. Anon says:

    Excellent post!! Please update more often from your stay with the hunter-gatherers, and MORE pictures;)

  19. mkzp says:

    Ok, I’m a little embarrassed here because maybe I’m just not smart enough to get it or maybe I missed something but can someone please explain to me what the article (although very interesting) was trying to say about microbes, health & longevity? The Hadza people have certain traditions and habits with regard to food preparation and consumption, yes, but how do those habits benefit them, compared to us? I didn’t read anything (again, maybe I missed it) that said how they are particularly more healthy than we are. Or was that not the point of the article; how living a more ‘microbe-friendly’ lifestyle makes for better health? I agree we are way to ‘sterile’ in modern culture, especially children, but I don’t get the point of expounding the Hadza’s habits as an example of better living. What am I missing?

  20. Tatertot says:

    If you don’t eat EVERYTHING those guys are eating, no matter how gross–you will regret it for life! Just. Do. It. We are living vicariously through you on this!

    1. Jeff Leach says:

      True that. and in time, i’m sure everything will be on the menu for me. gulp.

  21. Alan says:

    This was a very interesting article–thank you. I shared it with my class–about 200 undergraduates in an intro-biological anthropology course. We enjoyed it very much! My wife laments the loss of traditional behaviors of passing microbes.

    We have some questions for you.

    There was a seeming contradiction with respect to fat. The Hadza men really enjoy eating the fatty organ meats. I suspect that their diet (Hadza men, and women to a lesser degree) is even higher in fat than the mouse chow high fat (40% of total calories), and yet I don’t suppose that they have much obesity. But the mice eating high fat and sharing poo with skinnier mice remained fat. Moreover, I doubt that the Hadza would suffer the same fate in this situation.

    What is the source of the fat in the mouse chow diets (lard, soybean, olive oil, trans-fat, etc..)?
    It could be different sources of fat and poor quality sources. There might even be different sources of fat between the treatment groups in the same study! I emailed the author from the Science paper above and asked about the sources of fat.

    Thank you so much for the fascinating work.

    1. Jeff Leach says:

      Wow. Very cool your shared with 200 students. Great Qs – short answer, dunno. Note we will be transplanting poo from Hadza from various times of the year – read different seasons and thus different %s of key resources – into germ free mice. This will be interesting. Note that despite the fact that Hadza consume >50-75% of their calories from honey for certain months in the wet season, and eat almost nothing but berries on end during other periods, and lots of meat during dry season, and so on – their BMI remains more or less constant (~20 for men and women – note Marlowe’s group has estimated body fat for men ~11% and women ~20%). The fact that BMI does not fluctuate through seasonal “pulses” in macronutrients is very interesting. I’m gonna go out on a limb – a long and skinny limb – and suggest that maybe the gut bacteria help energy intake throughout the year. We will explore this when we transplant hadza poo into germ free mice. I wouldn’t focus too much on the fat in the diet of the mice. I think it has more to do with the qty and quality of the plant material going up and down. As for the Hadza and human-microbe evolution the key word is seasonality – that is, if i could pick one word that characterizes our evolution it’s seasonality. With a nod to Richard Wrangham, I think seasonality made us human.

  22. Sylvia Maes says:

    We noticed that both our family and those we gave eggs to when we first got chickens often has some digestive issues from the eggs.With time we got used to the eggs or perhaps inoculated with the chicky microbes and have since not had any digestive issues. I am careful to give the eggs to healthy friends and not subject them to dirty eggs from wet and rainy days. We also eat veggies straight from the garden, a garden that often has chicken trespassers

    I think there is great wisdom in slowly shifting gut microbes. It is important to not add larger buggies by mistake too, parasites

    I only ask my kids to wash hands when returning from school. My gut feeling. is that the reliance on hand sanitizer and Clorox wipes makes for wierd and potentially sickly microbe sharing at school and from the greater kid community.

    Thanks for the intestinal update.

  23. Mary Salazar says:

    Are any studies done on actions near or in the appendix of the Hudza tribesmen?

    1. Jeff Leach says:

      not that i know of.

  24. Jenny B. says:

    I think that 20% child mortality rate is pretty significant (in the U.S. our under-5 mortality rate is .07%). Those who are not adapted to the harmful microbes (gut and otherwise) do not survive to adulthood.

    1. Jeff Leach says:

      yup. it’s high. but it is likely the norm for a big swath of human evolution – actually low. but doesn’t change the conversation about their and our relationship to the microbial world. note it’s also not about being adapted to the microbes. in the west, we fight it with medications – medications the hadza don’t have access to. without those medications, i often wonder if “western” kids with their less diverse gut microbiomes (which means less resilience) would succumb to infections at higher rates than say the hadza. thanks for commenting on blog post… comments like yours make us all smarter – or at least makes us think more…. in addition, part of the point in the post of asking people not to make too much of the child mortality is draw attention to the human-microbe relationship in an ancestral setting. note if the kids make it to adulthood, they have a good chance of hitting the golden years. it’s also important to note the hadza don’t suffer from diabetes, cancer etc… at any appreciable amounts… that’s the point i’m trying to get at. how much of it is diet – which is what we focus on in the west – and how much of it can be attributed to their intimate participation in the microbial super highway… nobody knows… but we are chipping away at it one poo sample at a time…

  25. js290 says:

    Mathematics, the tool of science, tells us coupled systems cannot be decoupled. The Hadza obviously understand this and live and thrive within the bounds of Nature. “Modern, civilized” people are constantly trying to decouple these coupled systems. This is even illustrated by the mice study you cited conducted by so called professional “scientists.”

  26. Awesome article! This is one of the firsts I have read to touch on my theory “don’t drink water that has been treated with chlorine and fluoride”. Many municipalities also use chloramines which are like chlorine on steroids and cant even be boiled out.. I believe city water kills valuable bacteria. Much of which takes much effort to cultivate. I have never been healthier since embracing my current diet which is diverse in many fermented foods and sprouted grains.

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  28. Mike says:

    Sally Fallon wrote about this in her cookbook Nourishing Traditions:

    According to John (Fire) Lame Deer, the eating of guts had evolved into a contest. “In the old days we used to eat the guts of the buffalo, making a contest of it, two fellows getting hold of a long piece of intestines from opposite ends, starting chewing toward the middle, seeing who can get there first; that’s eating. Those buffalo guts, full of half-fermented, half-digested grass and herbs, you didn’t need any pills and vitamins when you swallowed those.”
    -John (Fire) Lame Deer and Richard Erdoes, Lame Deer Seeker of Visions, Simon and Schuster, 1972, page 122

    Probably eating gut flora of our prey was a widespread practice in our ancestors. Why not eat what our prey ate? You can’t afford to waste anything when you are a hunter-gatherer.

    1. Jeff Leach says:

      great quote. thanks for sharing… maybe us moderns should be eating a few more colons…. but would likely need to start the preparation of our own guts at birth…

    2. paulvzo says:

      I came here from . I was going to make a comment about the buffalo and the plains Indians, but you brought some of it up first. I recently read “Imagining Head Smashed In,” a book written a man who has spent his entire professional life studying the Canadian buffalo jump site of that weird name. Our knowledge of how they utilized the buffalo, both pre and post horse introduction, is immense, coming from both early whites and oral traditions.

      The PDF is free.

      They absolutely used the stomach and intestines in almost identical ways as the Hadza! Stomach contents were also used to “tan” the hides.

      My sister is a clean freak, although she does have some cats. OTOH, I only wash my hands when physically dirty or in my every-two-or-three day showers. I don’t wash my veggies and my hands “contaminate” my salads.

      While n=2 is poor science, guess which of us is always going to the doctor? (Even excluding female reasons.)

      I’m 67 and have always believed the old adage about eating a pound of dirt before you die. Maybe 20 pounds?

  29. David says:

    I know that this is just one blog entry, so understandably you can’t cover everything, but the overall tone of your piece overlooks the considerable downside of cleanliness. Yes, you do pay short attention to the benefits of modern sanitation introduced for the most part in the early 20th century. But this is a major milestone in the human condition. The elimination of harmful parasites that kill newborns (and adults too) should not be dismissed or diminished. There has to be balance between increasing our exposure to helpful bacteria without assuming we have to live like the Hudza.

    1. Jeff Leach says:

      correct (i’m hyper aware of the downsides and hygiene, sanitation etc – address in the piece). but it’s useful to remember that harmful bugs appear by all estimates to more of an issue throughout for populations that are settled and dense – which introduces important opportunities for pathogens. more nomadic populations – presumably much of humanity prior to domestication of animals/plants etc – are not subjected to the same problems – at least not to the degree we see is more sedentary groups. you are correct, bugs kill – and they kill hadza as well. And you are correct again, dangerous balance between too much exposure. and at the end of the day, not suggesting we live like the hadza but rather they provide an amazing opportunity to explore the implications of gut microbial resilience in the context of an extraordinary exchange of microbes with the environment – something all humans once did. efforts like ecosystem restoration (aka fecal transplant) would be made more interesting if we better understand the baseline resilience that humans are “supposed” to possess. the hadza might help. even more interesting, the early childhood exposure to the larger microbial metacommunity throughout human evolution (and the hadza) will likely be very informative. thanks for the great comments…

  30. Anna Hielm-Björkman says:

    Hi you guys. VERY interesting things. Three comments: at least in Europe tripe is still a delicacy with old folks and I guess it is a VERY old tradition as all parts of the animal protein always was used in all hunted or cultured animals as food was more scare then than it is now. Nothing was ever thrown away.
    Comment two: Nowadays parts of it is frozen for raw food consumption in dogs (and seems to be excellent as a intestinal microbiota support!).
    Comment three: It has been shown that people share more of their microbiota with their dogs than with their children. Your hunters there seem to share more microbiota with their prey than many of us. This will of course make their immunity be the same as their pray animals and thei will become immunized against diseases that might otherwise be harmful… a type of ancestral vaccination.
    I guess the first yougurt was made when hunting a mother animal with udders filled with milk and then carrying it home using hands “washed” with intestine content (filled with lactobacilla and others) and having it jump up and down (=mixing it) while walking home….
    Keep us posted.

    anna from Finland

    1. Anna, you’re very right about the origin of yogurt! Yummy!

  31. Just absolutely fascinating.
    I think a lot about the subject of human/microbe interaction. I keep chickens and goats, dogs and cats. The dogs eat chicken and goat poops and share our beds. My rat terrier has a penchant for “cleaning” our noses with his little tongue. He is quite insistent about it. I let him go as long as I can stand, and I can smell whatever recent poop is on his breath. The idea of the microbial transfer isn’t what bothers me, it just feels weird.

    I also make and eat a lot of lacto-fermented veggies. I am careful about hand-washing around food preparation. Maybe I shouldn’t be! I never get sick anymore, in contrast with when I worked in a busy newsroom in San Francisco. I am under more stress now in some ways and still short on sleep sometimes, but I never get sick. I also eat well and minimize sweets.

    I look forward to more reports on the Hadza. Thanks!

  32. Grace/Dr.BG says:

    I’m bummed Jeff that you didn’t partake of the raw stomach or intestinal sashimi!

    lol ahaha. I wrote to you earlier about my Prevotella. Did you see? How was yours calculated (prevotella/total)??

    1. Jeff Leach says:

      Thanks… Not sure i saw early comment on prevotella. My Prev levels are ~1% — determined by 16S rRNA sequencing of my stool.

  33. Grace/Dr.BG says:

    Jeff — another question. How does American Gut Project determine the soil based commensals in the samples? Does it detect strains commonly found in ancestrally prepared fermented foods… Bacillus licheniformis? Clostridium butyricum? E. limonus? THX!

    1. Jeff Leach says:

      We don’t identify to the species level, just to the genus…

  34. NAWM says:

    Hi Jeff, Could I email you somehow. I am in Australia and have a couple of questions

    1. Jeff Leach says:

      Sure. Jeff AT humanfoodproject DOT com

      1. NAWM says:

        Thanks, talk with you soon

  35. I appreciate that Jeff. It is so wonderfully and interested for everybody who see it and read it.You know what jeff, myself didn’t understand there other people around the the world through eating easily digested food they caused to killed a lot of bacteria,so Jeff this is big challenge to the world

  36. Bravo Jeff! Amazing to see just how much of positive reactions this is getting from your readers! The wild still resonate within us! Time the Decomposers were given some respect they deserve!

  37. Jim Beecham says:

    Does the Hadza exposure to the microbiotome of animals they hunt also expose them to phages? How much sharing of genes is possible in this manner?

  38. Elyse Singer MD says:

    Great article! Just curious if any of the Hadza have autoimmune diseases such as MS?

    1. Jeff Leach says:

      if they do, it doesn’t appear to b widespread…

  39. iana says:

    Great article, Jeff! I’ve also read some of your older entries and more than once you mentioned how a high-fat diet results in, as I understand it, a less than optimal imbalance in the gut flora wherein the body then has lower insulin levels and other things that indicate things aren’t working as they should or ought to. In short we should lower our fat intake and increase prebiotic fiber, right?
    So, my question is does the term ‘fat’ include fish oils; sources of EPA, DHA, EHA; those sort of things -the so-called Omega-3 Fatty acids that are food for our brains?
    Thanks (in advance) for answering.

    1. Cindy C says:

      Great article! In so many or my reading, the amount of fat will change the microbes, but many who go into a ketogenic diet, lose weight, although some gain. I changed my diet into a diet of 65-70% fat calories, about 25% animal protein, and the rest carbohydrates. The carbs were the vegetable/mushroom kind. The fats were from meat fat, butter, ,avocados, and coconut oil, so a mix of saturated, monounsaturated, and polyunsaturated. I also take cod liver oil. I lost weight, and keep it off, as long as I stick to the diet. .Really high fat and high refined carbohydrate diets do not go well together, The body can do well on a lot of fat, if your metabolism is “broken”.and you cannot burn glucose properly, but instead you find you can burn fat easier, and you lose weight, and so diabetics can do well on the diet The key is to keep the carbohydrates very low, low enough to burn fat and ketones instead of glucose. Most people can adapt to doing so, but it can take a few weeks for the body to switch. I would not want my insulin levels to be high, as I do not want my blood sugar to get too low, or my insulin producing cells to wear out. My body works completely different now, and in a better way. The brain is, according to science over 50% fat, and breast milk of mammals is about 50 % or more fat, and a lot of that is saturated fat.. The Hadza do not seem to be bothered by diabetes, and can probably easily switch from burning glucose, to burning fat, as their diet changes with the seasons, as their gut bacteria also changes then. They have not had the antibiotics that we have had.

  40. Fantastic work and presentation. My gut flora was entirely wiped out with antibiotics and my kids were born with horrendous digestive, allergic, psychiatric problems. Please let one mind 4 research have your data. The mental health of our world is teetering on the brink

  41. gabriella kadar says:

    So, if I feed some feces from my lithe Angora kitty to my somewhat porky male tabby kitties, maybe my tabby kitties will slim down? I think I’ll try it. Hide some skinny kitty cat poop in a canned catfood meatball and get it down their throats.

  42. Bill VanHorn says:

    This is the first article I have read on the subject.
    Has fecal transplant been tested in humans that you know of? Can you take fecal matter from a thin person and implant it into the colon of a obese person?

    1. Jeff Leach says:

      yes, lots of research on this. just google the topic – lots of peer reviewed material.

  43. Jeff, I’ve read your work with fascination, but find it odd you haven’t addressed the findings of Weston A. Price. His book “Nutrition and Physical Degeneration” provides the most complete record of anthropological nutrition that we have.

    A dentist who was head of a large research team for the ADA of his time, Price was well versed in the scientific method. He spent several decades studying traditional populations all over the world eating diets that were untouched by “the displacing foods of modern commerce”.

    Price found that a high fat, high animal food diet was the norm for the healthiest people from diverse climates, conferring a wide range of health benefits. Diets high in animal fats provided exponentially larger amounts of key fat soluble nutrients – vitamins A, D, and K2 – than a plant based diet does. And acting as catalysts, the trio enables one to actually utilize all other vitamins and minerals.

    It leaves me feeling that your research is trying to adhere to the current trend in popular science, i.e. plants good, animals bad.

    Or perhaps it is just impossible for you to find a remaining population that is eating according to this ancient wisdom today. Are there current Masai tribes which still adhere to their traditional diet of just meat, milk and blood?

    P.S. I also find it strange that the Hadza reserved the highest nutrient foods for their men, while other cultures studied by Price routinely saved their women special foods, such as organ meats and fish eggs, for ensuring the birth of healthy children.

    1. Jeff Leach says:

      thanks for the great comments. very familiar with w price. as for my “research is trying to adhere to the current trend in popular science, i.e. plants good, animals bad.” couldn’t be farther from the truth. note my personal diet hovers around 50% fat etc. I’m a big meat eater – however, i’m a big plant eater as well. i focus on things/diets/lifestyle etc and the impact on the gut microbiota. 99.99% of the maasai have transitioned to a cash economy and maize-based diet. among the hadza, ~25% of the calories come from meat – more or less. however, this is highly variable – very seasonal. during the dry season more meat is consumed – but during the wet season more honey and plants etc… but again, highly variable. as for the mean eating a disproportional amount of meat – has some to do with men eating some of the meat at the kill site and some portions of the kill (organs) considered epeme meat (sensu epeme ritual). this is well documented among the hadza by researchers stretching back 100 years.

      1. Jane says:

        Thanks for that clarification. I was responding your Pollan quote to “eat mostly plants”.

        And yes, meat is not necessarily as important as fat as Weston Price showed.

    2. This is about microbiomes and not teeth. Weston Price has not lived with the Hadza, and has nothing to do with the latest research as performed by Jeff. I feel you show a complete lack of respect!

  44. Heidi Fink says:

    Wow, wow, WOW! SO interesting! I have been fascinated by the wealth of research emerging about the importance of our gut flora.

    1. Double Wow. I had a friend that cultured her baby’s poo for her grad school project. This is so necessary. Human Ecology Action League just published some disturbing findings about glyphosate (Roundup) disturbing gut balance. I haven’t read the research but it sounds ominous.

      1. Jeff Leach says:

        Thanks. Do you have a reference for roundup-gut research you mentioned. Haven’t seen that.

  45. rtw208 says:

    wonder if eating the antelope poo helps them digest the heavily fibrous diet they so eat. are some of the plants they eat in the antelope diet?

    1. Jeff Leach says:

      i’m pretty sure – though don’t have the data yet – that the hadza’s intimate interaction with the larger, metacommunity of microbes amongths the plant and animals is a source of microbial diversity. we will see.

  46. BrianL says:

    Reading this I cannot help but think of my two 4 and 5 month old Border Collies. They constantly eat dirt and roots in the grass as well as the other “things” dogs eat. They Are very healthy living out here in the Northwest Washington forest.

  47. Megan says:

    Great article! I am curious about the relationships between gut bacteria and parasites. Several years ago, I traveled to a very remote town in Peru. Meat would be left out, most bathrooms didn’t have soap, the pipes were so narrow you put your used TP into a trash can, etc…what I’m getting at, is this place was pretty ‘wild’ and certainly wet-wipes-free. I met people who had contracted parasites before, but as an American, I was the only person getting bacterial illness from the food. I wonder, would there be a certain balance of bacteria in the gut that wards off parasites? I would love to know more about this topic across various cultures as well.

    1. Jill Swartz says:

      In the late 1970s I lived in a Dene community in northern Manitoba, Canada. I was invited to join a family who had killed a moose which they were dismembering inside their tiny log home. The family was honouring me, as a teacher, with one of the first portions. People of the community surrounded the home, peering in every window and awaiting their share… In the middle of the bloody floor, amidst the severed pieces of the animal, sat one of the daughters of the hunter with her happy child on her knee. She was feeding her child what was considered to be the delicacy of the kill: pieces of the raw stomach of the moose.

      1. Bob Dillon says:

        Early 90’s I lived in Alaska. Athabascan tribal elder “adopted” me. At gatherings moose stomach soup was always on the menu. I ate everything offered to me. I do not miss it but would gladly go back for more now knowing what I have learned here.

  48. zoltanwelvart says:

    Thanks for info.i found 2 meter deposit of plankton.microbe food.atlantis to mayan mined.i have sample of giant deposit that heavily influenced past citystates.books burnt, christianity demonizes this simple but powerful science.need money to continue research.

  49. Sara Pennant says:

    Fascinating project. Do the Hadza suffer from any kind of food allergies? Thanks

  50. I have been living on a tropical island in Thailand for almost 30 years directing a fasting course. Doing research for a section on the micro-biome for a book I am writing I came across your website and articles. I am truly intrigued and entertained by your research. I have a hypothesis I would like to share with you based on observations of my clients and on myself. I believe that when people are carrying a great number of toxic microbes and not enough of the friendly bacteria, when they are exposed to the friendly guys their body goes into an immune reaction–a fight between the toxic microbes and the good guys develops that inflammation and uncomfortable cleansing reactions occur. Once they clean out the colon, small intestines and liver, fairly well (a two to four week fast with colonic irrigation) they become hungry for the healthy micro-biome. I have seen this countless times with people and it is miraculous. . . From your experiences in the field I would love to get your perspective on this observation, or hypothesis. . Best of Luck with your Project!

    1. Tim Steele says:

      Hillary – I think you are spot on that the pathogenic microbes need to be removed before any healing can begin, but not with antibiotics!

      Here’s an experiment I did eating ONLY potatoes for a week, and then sent in a sample of poo for testing…amazing diversity created! A short fast and then hit it hard with fibers and resistant starch should be equally good.

      See here:

      Often in the tropics, green banana and High Amylose Maize is used in a similar fashion, the pathogens are attracted to the starch molecules and flushed from the system. Ie.,

  51. Jeff or Anyone,
    Which organisms produce which B vitamins in the human gut? This question is of vital importance. Lack of B1 causes Beri Beri. Lack of B3 causes Pellegra. These used to be common deficiencies until the food supply was supplemented. Each B vitamin deficiency has very specific and severe symptoms. Many of these symptoms could be treated with the right micro organism, rather than with massive doses of B vitamins.

  52. BarleySinger says:

    I also tend to wonder about the dental health of the Hadza (not due to a lack of sugar by the Kg). Flora has a large impact on dental health, but it ignored by most physicians and dentists.

    I have a large number of health issues (gut among them). I am also losing all my my teeth despite a lot of effort not to do so. They became very soft all at once (even soft rice caused them to break). Research shows that people who have my illness set tend to be very low in Threonine (which is necessary for the production of tooth enamel)

    1. david says:

      The Hadza have fantastic teeth, and I am sure they know why they consume copius amounts of wild honey, would the Italians pass the pizza?

      Our bodies have evolved to cope perfectly with honey and other sugars, I do wonder if fluoride is the cause of tooth decay?

  53. Really great blog – enthralling.

    Being Western, I’m interested in what it might mean for Western lifestyle – what microbes we should & shouldn’t have & how to get there.

    Is there a chance of a page listing findings that may have practical application to our health, as they accumulate?

    Thanks again.

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