In industrialized societies, the diet of cheap, low-nutrient foods is putting selective pressure on gut bacteria.
The intestinal bacteria of the inhabitants of industrialized countries are getting used, against their will, to the diet based on ultra-processed foods to which we force them. Genetic variants that make the microorganisms of the intestine more capable of digesting the starches of cereals, chips, snacks & co. they are establishing themselves in certain populations of bacteria that colonize our digestive tract: this is according to a study published in Natureaccording to which modern nutrition is exerting important selective pressure on the microbiota.
Genomes increasingly “homogeneous”
A group of evolutionary biologists from the University of California at Los Angeles used a new statistical method to identify, in the DNA of around thirty species of intestinal bacteria, the regions in which the same genetic variants spread most rapidly. In essence, scientists went looking for the regions of greatest “homogeneity”, which stand out against a background of great variety and differences that separates one species from another.
«Different species of E. colifor example, have separated from each other as much as humans have separated from chimpanzees” in the course of evolution, “and yet we call them by a single name. Despite this diversity, there are still shared fragments of DNA present in many hosts, comparable to a hidden thread that connects our microbiomes” explains Nandita Garud, one of the authors.
Our “brag”: bacteria specialized in maltodextrins
The 30 species of intestinal bacteria analyzed are the most widespread among 24 human populations from all over the world, but the selective pressure is not acting in the same way everywhere: from the analyzes it was in fact clear that in industrialized contexts different genetic variants were “favored” compared to non-industrialized countries. In industrialized countries, the spread of a variant specialized in the digestion of maltodextrins, carbohydrates deriving from corn, rice, wheat or potato starch through the chemical process of hydrolysis, widely used in ultra-processed foods, has particularly caught the eye.
Since these starches can only be produced industrially and their massive consumption has only begun a few decades ago, it is thought that our bacteria are strongly encouraged to develop a genetic profile capable of digesting them.
Advantageous exchanges
The spread of variants selected to break down ultraprocessed substances would have been favored by the mechanism of horizontal gene transfer, the movement of genetic material from one strain to another, a mechanism that allows, for example, bacteria to develop resistance to antibiotics very quickly.
