I often hear Paleo and Primal eaters say their shopping carts almost always look like that of a vegetarian grazing through the same super market when it comes to the non-grain veggies it contains. This comment – in my experience – often follows when addressing critics who say that a Paleo/Primal diet focused on fat and protein from animal products means whole, non-grain plants and their health-giving fiber, will be greatly reduced. Ancestral eaters time and again respond this is non-sense and that such a diet always includes a significant amount of fiber – often exceeding that of the average citizen or veggie and grain-focused eater! While I’m generalizing here a bit about the ancestral community, let’s explore this notion with data from the American Gut project.
American Gut Project is the largest, open source and crowd funded microbiome project in the world. I co-founded the project back in 2012 with Rob Knight – who is the scientific leader of the project and now based at UCSD (click here for Rob’s new book). The project allows members of the general public an opportunity to peek inside their gut and see who’s in there so long as they donate to the larger citizen science project (note we’ve also given away hundreds of kits to folks who could not afford to donate). Each participant receives a testing kit at home that is to be mailed back to the Knight Lab at the UCSD (Note we’ve also launched British Gut with our affable colleague Tim Spector in London). As part American Gut, we ask that each participant fill out (optional) an online questionnaire asking standard things like age, gender, do you have any diseases, when was the last time you took antibiotics, do you brush your teeth, do you live in a city or a rural setting, and so on. In addition, we asked them to keep track of the foods they ate for a week by recording the information using an online website that keeps track of calories and so on.
Because samples and data (questionnaire) are self-collected/reported, the American Gut Project is a cross-sectional observational study. In other words, it’s not ideal and full of biases – and the researchers running and collaborating on the study are fully aware of this. However, the large number of participants – at the moment >15,000 swabs have been sent out – and the kind of broad questions we are asking of the data, make it an excellent study for accessing the gut microbe variability across the planet for a range of diet and other lifestyle factors. More importantly, the project will help inform future, and more detailed, studies. Long live citizen science!
Of that 15,000 or so swabs mailed out, not all have been mailed back to the lab, even less have been sequenced, and even a smaller amount of those have had the data uploaded. To date, ~4,500 samples have been sequenced and the results uploaded. (Please note all publicly available data sets have been de-identified – that is, scrubbed of any personal information that might link a particular set of results to a particular individual).
As part of the questionnaire we asked people if they were Omnivores, Vegetarians, Vegans, and so on. Of the ~4,500 participants with sequenced and uploaded data, ~3,300 of them filled out the questionnaire with enough detail to assess their daily fiber intake based on food intake for a week. However, from this data we can’t tell if someone that has described him or herself as an Omnivore follows a Paleo or Primal strategy for eating. For this, I had to try and tease out the data from the comments column associated with the diet info.
Identifying the Vegetarians and Vegans was easy – they said so. This resulted in 77 Vegans and 116 straight up Vegetarians. Note also we had 206 Omnivores who don’t eat red meat (pescetarian). For the truly Paleo/Primal folks I queried for participants who self-identified as “paleo” or commented with something like “I follow a paleo diet” or “I’m primal” and so on. This resulted in 73 Paleo eaters. For the ones that did not clearly state they followed a Paleo/Primal diet, but said things like “I don’t eat grains” or “I try and follow Paleo most of the time,” I lumped them as Paleo-Like (n=137). While this is not a perfect way to go about great science, it does separate the non-grain eaters from the vegan and vegetarian folks – at least for the folks who provided enough info. The distinction of grain eaters vs. non-grain eaters is useful as whole grains – presuming these are consumed by our grain eaters (at least some of the time) – contain dietary fiber.
Below is a box-and-whisker plot of the results. The median daily fiber intake for our various groups is as follows:
Paleo-Like: 19 g/day
Omnivore: 19 g/day
Paleo: 25.1 g/day
Omnivore, but no red meat: 27.8 g/day
Vegetarian: 32.8 g/day
Vegan: 43 g/day
As you can see – at least for our not-so-great but interesting cross-sectional observational data – Vegetarians consume more dietary fiber than our Paleo folks and Vegans beat them all. Our Paleo-Like folks didn’t do much better than our run-of-the-mill Omnivores – coming in at an embarrassing 19 g/day, which is line with countless studies published over the years about dietary habits of Americans (which if you squint a little bit, suggests our data is tracking well and thus useful to consider in the “Who eats more fiber?” theme of this blog post).
So on the often vigorous defense by some in the Paleo community that they consume adequate amounts of dietary fiber, I call bullsh*t. At least for this little self-collected data set. I’m not saying that a Paleo or Paleo-Like diet isn’t healthy or been shown in numerous studies to be metabolically beneficial, I’m just saying the Paleo folks in this data set consume an embarrassing low amount of dietary fiber by USDA and evolutionary standards. According to the USDA’s Dietary Guidelines for Americans, adults should be getting 14 g/day per 1,000 calories consumed. If you are on a 2,000-calorie diet, this translates into 28 g/day. So this means 28-38 g/day depending on your gender – more or less. Seems only our navel-gazing tofu-slurping Vegans surpass government recommendations with their crunchy cuisine. But how does this stack against our evolutionary past?
I’m often asked what the most striking thing I’ve experienced or learned while working among the Hadza hunter-gatherers of Tanzania. Aside from their breathtaking contact with the microbial world around them, I would have to say their near-constant daily nibbling of dietary fiber has been a real eye-opener. Given that the Hadza live in a place in East Africa that presumably gave rise to our genus Homo – and they literally hunt and gatherer many of the same foods that humans have in this region for millions of years (and are literally covered in the same dirt) – their fiber consumption and its impact on their gut microbes has implications for us so-called modern humans in the western world. And given the huge impact dietary fiber has on modulating our intestinal microbes – see Justin and Erica Sonnenburg’s new book The Good Gut for an exhaustive and well-researched review of the literature on this – the fiber habits of the Hadza is relevant.
As always, I take great pains NOT to get mired in the heated discussions about “humans evolved and do great on many types of diets” and “there is no one Paleo or ancestral diet” and “humans haven’t stopped evolving and adapting.” I know this – I get it. But when we are talking about our immune system and the daily tango it plays out with our resident microbes (friend and foe), we can safely assume that a great many of the genes that we carry today – both human and microbial genes – were selected in area of the world where we spent most of our time evolving. Not only as the genus Homo, but as members of the larger, ancient primate community. That would be Africa and for the better part of the last few million years, East Africa would be specifically of interest.
That said, the fiber intake of the Hadza is useful to consider – especially in our work on their gut flora. The published data on Hadza fiber intake is scant and inconsistent (click here for an example). The Hadza consume foods in and outside camp, often on the go making it difficult to measure a handful of berries here, a piece of fibrous tuber there. But any researcher who has spent time with the Hadza will tell you, fiber intake is 1) high compared to western populations and 2) variable day-to-day and season to season.
Early researchers and travelers working or visiting Hadza Land commented on the large, or distended bellies of many of the Hadza children – often interpreting this as malnutrition. This couldn’t be further from the truth. In fact, it’s a function of fermentation of dietary fiber deep in the bowels of the children. Yes, they eats lots of fiber (but not from “leafy greens” per se). As we’ve started to quantify the fiber intake among the Hadza, I’ve been amazed at the amount of fiber the children consume (still accumulating data). The primary weaning food for Hadza kiddos is Baobab fruit – but maize meal as a weaning food is creeping into more and more families. Mixed with water – and wild honey if available – the concoction of ground Baobab flour (highly fibrous chalky innards and fat-rich nut inside) of the fruit is consumed daily – yes, daily.
Hardly a day goes by when Hadza women aren’t found digging up fibrous roots or sucking on the chalky and fibrous innards of the Baobab. And if it’s the right time of year, seasonal, and fiber-rich berries are consumed in large quantities. As the men walk to and from hunting stands – or practice encounter hunting where they walk around for tens of kilometers in a day – they do so while picking small handfuls of various fibrous berries and sucking on fibrous Baobab fruit, often just lying on the ground under and endless sea of Baobab trees.
As we’ve started to quantify the fiber intake among the Hadza, some surprising and striking patterns are emerging. On any given day, a 4-48 month old kiddo might consume between 30-150 g/day of dietary fiber (sometimes more!) and out pops the distended belly (especially among the youngest in the camp). This is directly related to microbial actions deep in their bowels where the microbes go about breaking down the fiber releasing short chain fatty acids, various gases and other byproducts in the process – all of which promote the direct growth of some microbes and the growth of others through cross-feeding. Again, fiber intake is highly variable.
Adult daily averages vary greatly as well – but are high. As children become older and more foods are introduced into the diet (and young boys start hunting), the ratio of fiber intake to calories consumed seems to drop – but still well above that 14 g per 1,000 calories recommended by the USDA. Which brings up another question: why don’t USDA dietary guidelines include recommendations for Americans under two years of age?
I’ve asked around about this and can’t seem to get a clear answer. As best I can tell, it seems to be rooted in some notion that kids under the age of 2 are still consuming some or a large part of their daily calories from breast milk (but I could be wrong). As breastfeeding rates have plummeted in the US and elsewhere, this notion seems to be a little outdated.
Even more striking about the Hadza is the nearly constant nibbling of fibrous sources even in the presence of large quantities of other resources like meat and honey (personal observation). This has huge implications for modern health and well being, specifically with regards to the design of diets in microbial studies. Time and again, microbial studies finger meaty and sugary diets as having deleterious affects on resident microbial communities in the human gut and thus the overall health of the host.
Interestingly, these studies will often challenge a group of people or mice with a high fat diet – not unlike some Hadza gorging on a zebra kill eating the fatty brain, various other organs and marrow – but will not include any fiber – or if they do, in tiny amounts. While the studies may be mimicking what might be considered real world conditions – that is, the American diet – it ignores our evolutionary past and role of fiber in mitigating/blunting some of the deleterious impact of the fat-fed microbes. Said differently, would be great to see some studies that challenged mouse and man to high fat diets, but in a mixed meal with evolutionary amounts of fiber. I suspect the outcome would be very different as would be the headlines in your local paper.
As a side note, the most abundant genera or group of bacteria in the American Gut Project is Bacteroides of the phylum Bacteroidetes. In countless studies that see similar findings, it’s suggested to be a result of our high fat and sugar American/western diet. Interestingly, Bacteroides are a minor group of bacteria in the gut of the Hadza – even during periods of high fat consumption (dry season when animals are easier to kill) and during periods when they eat tons of sugar (honey and sugary berries are more abundant in wetter periods). Since some species of Bacteroides are pH sensitive – that is, the more acidity the less Bacteroides you might see – then we might expect to see less in the Hadza as the higher fiber diet means more fermentation which translate into more things like short chain fatty acids and greater acidity. And that’s exactly what we see. But at this point, we don’t know the true reason for lower abundance of Bacteroides in the Hadza gut.
Side note: it’s hard to wrap my head around the idea that sugar intake has such a huge impact on the distal gut microflora as sugar and its relatives is absorbed in the upper GI tract – well before it reaches the colon and could have an impact on the distal gut microbes. This isn’t well understood and would be interesting if it were explored in a little more detail. Maybe its a downstream effect – that is, shifts in communities in the upper GI that in turn have a downstream impact on more distal communities of microbes in the colon. Or maybe it’s the absence or low intake of fiber as sugary things make up as a larger portion of the diet is the bigger issue/problem. That is, it’s not what we are eating, but what we are not eating: fiber.
Paleo brothers and sisters you need to get your sh*t together (pun intended) and start trying to eat more fiber if you want to truly eat a more microbially relevant ancestral diet. That goes for all of us. If you don’t or can’t, then even the most ardent among the ancestral movement should be labeled Paleo-Like or Paleo Lite.
In closing, us so-called modern humans probably have the most alkaline guts in human history because we don’t eat enough fiber – not even close. I’m gonna go out on a limb here and suggest that the big bellies of these Hadza kids is trying to tell us something about the importance of an acidic colonic environment early in our development – specifically in this 4-6 month window when they – and presumably all of us – started receiving our first non breast milk foods. This, coupled with their microbially-rich environment – contrast that with the hyper-sterile environment our kids live in today – may hold the clues to the rise in some of the terrible diseases our children are afflicted with so early in life. If this die is cast early in our immune system development, then it has implications for our health as adults as well.
If I had to pick one thing – among the myriad of dietary decisions we are faced with on a daily or weekly basis – making our colonic environment more acidic would be at the top of the list. By doing so, our more acidic colons will mean better barrier function (less leaky gut), a more hostile environment for potentially pathogenic bacteria, and a greater diversity of microbes. Smile. Your next meal is fast approaching.
***Please note I do not have an agenda with this post. As anyone who reads this blog knows, I’m a big fan of all things Paleo. And a big-time eater of all things flesh.
*** We are developing an APP with colleagues to help you feed and nurture your microbiome a little better (think diet + other lifestyle factors). If you want to receive an email when the Beta is ready, click here.