Science News has a fascinating short story, Gut bacteria reflect dietary differences, by Gwyneth Dickey, that highlights one of the ecological dimensions of ‘enculturation’ that I think some symbolic models of culture have a hard time grasping. It turns out that a Western diet produces a less-varied gut ecology in Italian children than was found in African children. Moreover, the old adage ‘you are what you eat’ could apply in a particularly interesting way to those who eat termites.
The original article, Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe (urban Florence) and rural Africa (Boulkiemde province, Burkina Faso), by Carlotta De Filippo and colleagues, is open access on the Proceedings of the National Academy of Sciences website, so you should definitely surf over there if you find this interesting.
De Filippo and colleagues discuss the microbiome, the ‘complex consortium of trillions of microbes, whose collective genomes contain at least 100 times as many genes as our own eukaryote genome’ (see also Gill et al. 2006). This enormous, varied ecosystem in the gut, a symbiotic community, supplements human metabolic capabilities, provides a first line of defense against pathogens, modulates gastrointestinal development and even informs the configuration of the immune system (paraphrased from De Filippo et al. 2010).
Different gut ecologies brought about both by environmental factors and by food production techniques, dietary preferences, and even food handling practices are one way that human groups might inadvertently induce biological variation in our species, a subtle culture-biology link through the populations in our gastrointestinal tracts. Now De Filippo and colleagues has gone out and actually demonstrated this variation empirically, using high-throughput 16S rDNA sequencing and biochemical analyses of fecal microbiota.
What’s on YOUR plate?
In Burkina Faso, children’s diets after weening were ‘low in fat and animal protein and rich in starch, fiber, and plant polysaccharides, and predominantly vegetarian.’ Diet was primarily composed of cereals (millet grain, sorghum), legumes (black-eyed peas), and vegetables, providing ample amounts of nonanimal protein, carbohydrate and dietary fibre (children in Burkina Faso were getting more than three times the fibre eaten by the comparative population from Italy).
The children in Burkina Faso got very little animal protein, primarily a bit of chicken from time to time and, during the rainy season, termites (also interesting because of their role in chimpanzee diets, but we’ll be back to the termites because they’re the punchline of the article).
In contrast, the Italian children, after being weaned at an earlier age, on average, were taking in a diet much higher in animal protein, sugar, starch, and fat, with lower fiber (in part due to greater food processing) and much greater energy.
Startlingly, the children, 2- to 6-years-old, in Burkina Faso got 996 kcal/day compared to the Italian children who were eating 1,512.7 kcal/day; even prior to the age of 2, children in Italy were taking in an average of 60% more calories than Italian children! (This also harkens back to our discussion of what makes WEIRD populations truly odd.)
The community inside them
The faecal samples from children in Burkina Faso especially differed from the Italian subjects because of the presence of Prevotella, Xylanibacter (Bacteroidetes), Treponema (Spirochaetes), and Butyrivibrio; all appeared in the African samples but were not found in the Italian. The researchers hypothesize that these distinctive bacterial genera might help to extract energy from the polysaccharides in the children’s heavier fiber diet. Theses bacteria are capable of fermenting cellulose and xylan through a number of carbohydrate-active enzymes, producing anti-inflammatory effects at the same time.
From the Science News article by Dickey:
Children from Burkina Faso, who ate millet grain, sorghum wheat, legumes and vegetables, had high numbers of bacteria that digest plant fibers. Also found in the guts of termites, these bacteria break down fibers that humans typically can’t. The bacteria make short-chain fatty acids that give people energy and protect them from inflammatory gut diseases such as Crohn’s disease and inflammatory bowel disorder.
Burkina Faso’s children also had decreased numbers of diarrhea-causing bacteria compared with children from Italy. That finding surprised the team, because the African children often drank water polluted with such bacteria.
The diminished diversity of microbiota in the human gut is especially interesting because some theorists have pointed to this dietary-provoked transformation, together with increasing hygiene and anti-bacterial technologies in human environments, as possible contributors to an upsurge in rates of allergies, auto-immune disorders and inflammatory bowel diseases (see, for example, Strachan 1989). Recent research has suggested a relationship between ecological imbalances in gut microbiota and obesity, and inflammatory conditions in the bowel have been directly linked to changes in gut microflora. For example, bacterial species correlated with a high-fat, high-sugar diet promote obesity in gnotobiotic mice (Turnbaugh et al. 2009). In other words, the diet can have a twin-pronged attack on our ability to maintain low body weight, as it provides both higher calories as well as a shift in microbiota to a population that promotes obesity.
The team led by De Filippo compared the diversity of microbial life in the fecal samples from both locations, finding that the African samples, by several measures, had greater diversity and richness of symbiotic life.
Exposure to the large variety of environmental microbes associated with a high-fiber diet could increase the potentially beneficial bacterial genomes, enriching the microbiome. Reduction in microbial richness is possibly one of the undesirable effects of globalization and of eating generic, nutrient-rich, uncontaminated foods. Both in the Western world and in developing countries diets rich in fat, protein, and sugar, together with reduced intake of unabsorbable fibers, are associated with a rapid increase in the incidence of noninfectious intestinal diseases. The potential protective effects of the diet on bowel disorders was first described by Burkitt  who, working in Africa in the 1960s, noticed the remarkable absence of non-infectious colonic diseases in Africans consuming a traditional diet rich in fiber.
The fact that the youngest children in both populations had similar microbial profiles in their GI system suggests that diet primarily is effecting the difference between the two populations; while both groups are still breastfeeding, they are more similar, only diverging later when they start to eat their distinctive cultural diets.
Horizontal transfer of microbial life
The short piece in Science News makes clearer, in my admittedly non-specialist reading, an interesting little wrinkle in the story of diet affecting gut microbiota: the horizontal transfer of microbes from our food to our own guts. As Gwyneth Dickey writes:
A termite a day may keep the doctor away. African children who eat a high-fiber diet (and the occasional wood-digesting insect) have gut bacteria that help them digest plant fibers and protect them from diarrhea and inflammatory disease, a new study finds.
What I’m struck by here, and I’m not sure if this is Dickey’s interpretation or something one of the researchers said, is the suggestion that some of the microbes most able to turn whole grains into short chain fatty acids might be colonizing the large intestines of children in Burkina Faso through the rainy season practice of dining upon termites! (She quotes co-author Duccio Cavalieri warning, ‘We’re not saying you should eat termites,’ but it’s unclear where the original suggestion might have come from – Dickey or the research team.) I have absolutely no idea if this is actually possible, but there is the case of microbes being transferred from food to Japanese individuals who dine on some forms of algae (see Hehemann et al. 2010).
The more I think about this possibility – that we might pick up symbiotic microfauna by eating the guts of other animals – the more I find it both weirdly fantastic and simultaneously plausible. After all, what living organism is more likely to survive the digestion process to colonize the human gut than a microbe that’s already adapted to the gastro-intestinal tract of another animal?
But if it’s happening, we have a case where children are picking up microbes that will live in their guts and help them to digest dense fibrous foods by eating termites. What could be a better example of a kind of dietary ‘contagious magic’ than eating an animal and gaining some of its distinctive powers of digestion?! Eating termites might make it possible for your body to digest ‘woody’ food sources.
It’s not the gut, but I’ve written about the microbial life on the skin back in The human ‘super-organism’.
Gut population cartoon originally from Yakult.
Burkitt, D. P. 1973. Epidemiology of large bowel disease: The role of fibre. Proceedings of the Nutrition Society 32:145–149. doi:10.1079/PNS19730032
De Filippo, Carlotta, Duccio Cavalieria, Monica Di Paolab, Matteo Ramazzottic, Jean Baptiste Poulletd, Sebastien Massartd, Silvia Collinib, Giuseppe Pieraccini, and Paolo Lionetti. 2010. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proceedings of the National Academy of Sciences. Published online August 2, 2010. doi: 10.1073/pnas.1005963107.
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Hehemann, J. H., G. Correc, T. Barbeyron, W. Helbert, M. Czjzek, and G. Michel. 2010. Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota. Nature 464:908–912. doi:10.1038/nature08937
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Turnbaugh, Peter J., Vanessa K. Ridaura, Jeremiah J. Faith, Federico E. Rey, Rob Knight and Jeffrey I. Gordon. 2009. The effect of diet on the human gut microbiome: A metagenomic analysis in humanized gnotobiotic mice. Science Translation Medicine 1:6ra14. doi: 10.1126/scitranslmed.3000322