If you eat non-vegetarian food items (or obese ) chances are that you might have Firmicutes bacterias inside your bowel system which helps breaking down those huge protein molecules to get the most out of the food. And if you are a vegetarian you mostly have Bacteroidetes, a family that specialises in digesting plant molecules.
But breast milk isn’t just a meal for baby, but for baby’s first gut bacteria. After lactose and fat, the third most common ingredients in breast milk are small sugar molecules called ‘oligosaccharides’. Gut bacteria thrive on these and Angela Zivkovic from the University of California, Davis thinks that they evolved as part of breast milk, to selectively feed the right bacteria in a baby’s bowels.
Breast milk contains over 200 types of oligosaccharides. They’re part of a baby’s immune system by acting as decoys for disease-causing bacteria. They look like molecules on the surface of human cells, which infectious bacteria recognise and stick to. By presenting alternative targets, the oligosaccharides divert these bacteria away from actual cells.
Of course, diet is just one of many traits that separate children from the Netherlands and Burkina Faso, including genes, hygiene and climate. But the youngest babies in de Filippo’s sample show that diet wields by far the greatest influence on the microbiome. The toddlers, unlike their older peers, all ate the same food – breast milk – and as a result, their microbiomes were very similar to one another’s, despite the gulf of differences between their cultures. It’s only at the point of weaning when their diets diverged that their gut communities did too.
The African children also had a greater diversity of gut bacteria, which probably hitch a ride into their bodies via their food. In Europe, generic, uncontaminated food presents a blockade to bacteria from the outside world, which means that Western gut communities have become gentrified. They lack genetic diversity, and they have few ways of increasing it.
This is bad news, for bacteria from the outside world provide a reservoir of useful genes that could help the microbiome to adapt to unusual diets.
But De Filippo thinks that the problems are bigger. An unbalanced or simplified microbiome could be damaging the health of Westerners more directly, affecting the risk of a variety of other medical conditions, including allergies, inflammatory bowel disease, bowel cancer and obesity. A diverse microbiome could also prevent more harmful species from setting up shop – indeed, and somewhat unexpectedly, food poisoning bacteria like Shigella and Escherichia were less common in the Burkinabe children than the Dutch ones.