Our digestive tracts contain hundreds of species of bacteria that aid in the breakdown of food and also make small amounts of some vita­mins. These bacteria also help maintain normal immunity and help the body fight a wide range of infections.

Over the past couple of years, research on people and animals has suggested that an imbal­anced ratio of some of these bacteria might also be a factor in obesity. For example, thin people tend to have large numbers of bacteria from the Bacteroidetes family, whereas obese people have a greater preponderance of bacteria from the Firmicutes family.

Now, a team of researchers has shown that specific dietary habits seem to favor one family of bacteria over the other with a variety of implica­tions for health.

Paolo Lionetti, MD, of the Meyer Children Hospital in Florence, Italy, and his colleagues compared the fecal bacteria in European children and those from children in a rural African village. Fecal bacteria are representative of those found in the digestive tract.

Lionetti noted that the diet of the rural African children was similar to that of people liv­ing thousands of years ago at the very beginnings of human agriculture. The rural African diet is very high in fiber.

Bacteria from the African and European chil­dren differed significantly. Samples from the African children were very high in Bacteroidetes and very low in Firmicutes bacteria – 73 to 12 percent. In contrast, samples from the European children consisted of 51 percent Firmicutes and just 27 percent Bacteroidetes.

The African children also had species of bacte­ria that were especially efficient at breaking down dietary fiber, so the carbohydrates in them could be used for energy. Lionetti noted that these bac­teria probably co-evolved with the dietary habits of rural Africans. These fiber-digesting bacteria were not present in the European children.

Lionetti noted that some of the differences in bacteria would protect the African children from infection and inflammation. These children had lower number of Shigella and Escherichia bacte­ria (which are potentially infectious), compared with the European children. Lionetti added that “increased gut microbial diversity and reduced quantities of potentially pathogenic strains” of bacteria could improve resistance to infection.

Reference: De Filippo C, Cavalieri D, Di Paola M, et al. 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 of the USA, 2010;107:14691-14696.