If aliens were to examine a human, they would think we were just slavish organisms designed to feed microbes and carry them around. Our bodies contain 10 times more bacteria than cells, and there are an estimated 3.3 million genes in the total bacteria DNA, which is 160 times the number of human genes. Our intestine hosts about one kilogram of bacteria, which help to digest and metabolise food, produce vitamins and protect us from infections.
The above is textbook knowledge, but many recent studies have uncovered new and unsuspected roles for these little companions. There is evidence that gut bacteria can protect or predispose us to pathologies ranging from inflammation to diabetes and obesity. And, as far-fetched as it sounds, a remarkable amount of data shows that they can even modify our mood and behaviour.
Microbes are hot on the scientific agenda. In May, the U.S. government launched a National Microbiome Initiative with an overall budget of a half-billion dollars, while the EU is funding more than 300 projects related to the microbiome.
Yolanda Sanz, a researcher at the Institute of Agrochemistry and Food Technology (IATA) of the Spanish National Research Council in Valencia, Spain, coordinates MyNewGut, the largest EU consortium in the field with 30 partners in 15 Countries. We asked Sanz about the perspectives of research and the intriguing connections between the microbiome and the brain.
What makes our gut flora, and how does it change over time?
Our intestine hosts a complex ecosystem of bacteria; we call it the gut microbiota, which includes at least 1000 species. We get most of our gut microbes soon after birth, although there is evidence of colonisation even during prenatal life.
Over the first two to three years of life, the microbiota is very unstable in its composition. This overlaps with a period in which the immune system is still immature. At this stage, the microbiota is greatly influenced by diet, for example whether you are breastfed or not.
With an adult diet, the composition of the gut microbiota becomes more stable and a microbiotic profile emerges. This usually prevails until old age when the diet diversity decreases and becomes more unstable, such as in babies. In some way, the evolution of microbiota reflects our growth and senescence.