Bacteria aren't all bad for human health. Plenty of friendly bacteria are hard at work in your gut right now, performing a wide range of essential functions, such as food processing and nutrient synthesis, out-competing pathogenic microbes, and boosting the immune system.
Your diet affects the microbial community within your gut, through essentially unknown mechanisms. Neither do scientists understand the relative importance of diet in relation to geography, hygience, climate, or sanitation.
Since the microbial community in your gut is so essential, these questions are important public health issues that are relevant to the long-term health of modern civilization. Contributing to this need, Paolo Lionetti (University of Florence, Italy) and coworkers have discovered vastly different gut microbial communities among young children from urban Europe and rural Africa.
This is a very important discovery. It has long-term implications for the health, resiliency and adaptive potential of modern civilization.
The children in question.
The scientists studied 30 children, from 1 to 6 years old, half of them from urban Italy (Florence) and the rest from rural Burkina Faso (Boulpon). Nine children from each group were male.
None of the children had taken antibiotics or probiotics within six months of the study (this affects gut ecology), and had not been hospitalized within this time period either. Extensive questions regarding childrens' lifestyle and medical history were asked of all mothers.
None of the children were moderately or extremely malnourished (this also affects gut ecology). Fecal samples were collected for molecular harvesting, a surrogate for the essentially impossible task of collecting, visualizing, and characterizing all of the microbes in the sample.
Differences in the childrens' diet.
As you may imagine, the diet of a child from urban Europe is quite different from that of a child from rural Africa.
The children from Burkina Faso are basically vegetarian, eating little fat and animal-based protein, and more fiber, carbohydrates, and plant-based protein. They are breast-fed until they are two years old, and eat roughly 1000 calories per day from 2 to 6 years of age.
In contrast, the children from Italy eat a diet high in starch, sugar, fat, and animal-based protein, with little fiber. They are breast-fed until until they are one year old, and eat roughly 1500 calories per day from 2 to 6 years of age.
The children from Burkina Faso are geographically isolated. The scientists consequently propose that their diet resembles that of early humans in Africa.
Differences in the childrens' gut microbial communities.
What effect may these dietary habits have on the microbial communities in the childrens' guts? This is discussed next.
There was one similarity between the two groups of children. Over 94% of the bacteria were from four phyla (groups of classes): Proteobacteria, Firmicutes, Bacteriodetes, and Actinobacteria.
This is where the similarities largely end. Both groups of children had a different percentage of each bacterial phyla in their gut.
For example, Bacteriodetes was over 2.5 times as common in children from Burkina Faso (57.7%) relative to children from Italy (22.4%). On the other hand, Firmicutes was over 2.3 times as common in children from Italy (63.7%) relative to children from Burkina Faso (27.3).
Statistical analysis proves that these percentage differences are significant (i.e. cannot be explained away by random variability in the data). Also of interest is that three genera (groups of species) are present only in the children from Burkina Faso; the scientists speculate that this has to do with their high fiber intake.
The result that more Firmicutes and less Bacteriodetes are present in the guts of Italian children is especially noteworthy. It correlates well with the previous discoveries that the prevalence of these bacteria is different in lean relative to obese individuals, and changes when calorie intake is restricted.
The scientists' speculation that European children are predisposed to obesity is therefore reasonable. The Bacteriodetes:Firmicutes ratio may serve as a handy biomarker for obesity risk.
Furthermore, Actinobacteria are abundant in children from Burkina Faso up to two years old (the end of breastfeeding for this group), as well as in children from Italy up to one year old (the end of breastfeeding for this group). Previous studies have shown that Actinobacteria levels are a consequence of breastfeeding.
These two groups of children are clearly different in terms of geography, hygiene, climate, and sanitation; however, these effects did not clearly manifest themselves in terms of microbial ecology. Collectively, this is clear evidence that diet strongly affects microbial ecology in the gut of young children.
Consequences of gut microbial diversity.
Do any of these diversity differences have clear consequences for the childrens' health? This is discussed next.
The scientists found that the children from Burkina Faso have an enhanced microbial diversity in their gut. This could help them fight off infections better than the Italian children, who eat uncontaminated food, and as members of developed nations are also more prone to non-infectious bowel disorders.
With fewer bacteria to help them digest fiber, the Italian children are less likely to extract all the nutrients (e.g. xylose) available from the food they eat, lowering the amount of energy they can obtain from food. Their gut microbial communities are therefore less adaptable than those of children from Burkina Faso, reducing their utility in the long-term.
Implications.
The loss of gut microbial diversity is an undesirable effect of modern development, and may be deterimental to long-term health and evolution. An analogy can be found in keeping children excessively sanitary.
Limiting exposure to harmful bacteria early in life may hinder the child's resilience to harmful bacteria later in life. Similarly, exposure to a wide range of food (within reasonable health and safety guidelines) may help maintain gut microbial ecology for future generations.
This will aid not only long-term resiliency and adaptive potential (important in itself). It will also aid the search for bacteria that maintain human health, complimenting the search for new drugs and pharmacological targets.
for more information:
De Filippo, C., Cavalieri, D., Di Paola, M., Ramazzotti, M., Poullet, J. B., Massart, S., Collini, S., Pieraccini, G., & Lionetti, P. (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 DOI: 10.1073/pnas.1005963107