Human beings coexist with billions of microorganisms. This coexistence has been achieved over thousands of years of co-evolution. These organisms live on us or inside us. They are symbiotic microbial cells that have developed such indispensable functions for us that we can consider ourselves not as an isolated species but as true "metaorganisms". These can be defined as a set of organisms of different taxonomic categories that coexist and function in a coordinated manner, have evolved together, and derive benefits from this association.

We have several years in an all-out war against microorganisms in our environment and in particular in our own bodies. Today in the morning I heard an advertisement for a soap that promises to eliminate 95% of bacteria from our skin; another day looking at the shelves of a store, I found them full of "pure" products, stripped - or at least that's what they advertise - of any microorganism. We eat salads sprinkled with holy water, yogurt that is no longer yogurt because it is so clean. Also in the office, the classroom, the gym, or the street, it is common to see many people carrying bottles of "purified" water, filtered, ozonized, blessed, with the purpose of eliminating all kinds of microbes.

We have succumbed to the idea that everything we eat or that touches our skin must be sterilized. And we have a terrible fear of such small beings that have told us that they are there and are coming for us. We have taken a similar attitude with other aspects of food: we no longer sweeten with sugar, we do not consume anything that has the dreaded cholesterol, eggs are poison, potatoes and tortillas are fattening and many people in restaurants do not order what they really want in the face of disapproving looks and real harassment from others.

The set of species and populations of microorganisms that inhabit us are called microbiota and are so abundant that it is estimated that their genome is more than one hundred times larger than the genome that defines us as a species. The three billion base pairs contained in our genome (the DNA of each human cell) pale before the size of the microbiota genome. Most of these species - mainly bacteria and fungi - live in the digestive tract, especially in the intestine, where their population is estimated at 100 trillion (a trillion is one with eighteen zeros). In addition to the digestive tract, we can find microbiotas, slightly less abundant, but just as important in the nose and respiratory tract, reproductive tract, and very noticeably in the skin and accessory glands.

What are these organisms doing there and how did they get there? Most microorganisms colonized us at the very moment of our birth and immediate exposure to the postnatal environment. Although some of these microorganisms may be pathogenic, the vast majority of them are commensal (they benefit from us but do no harm) and symbionts (we derive mutual benefits). While the microbiotas of the digestive tract remain more or less stable, the microbiota of the skin shows interpersonal variation. Each of us seems to carry a microbial "fingerprint" that gives us identity: these beings are responsible, for example, for our smell (and hence an attractiveness to others), interaction with perfumes, susceptibility or tolerance to skin diseases, among other things.

To our misfortune, the different microbiota are very recalcitrant to study. Most of the bacteria and fungi that inhabit us have not even been identified. The inhabitants of the intestine sometimes cannot be cultured in nutritious jellies, are anaerobic, and inhabit the millions of diverticula, invaginations, and cavities in the walls of the intestine that we have not reached. Today, DNA study and characterization techniques, called metagenomics, have enabled considerable progress in the field and are shedding light on the complexity of these populations and their possible roles in human health/disease.

Several studies in mice and ruminants (cows) have shown that intestinal microbiota are very sensitive to external factors such as feed. Variations in the content and quality of fiber in the feed, for example, are capable of altering the type of species present. Fungi increase with exposure to complex plant materials (high fiber) and bacteria dominate in a grain feed (low fiber, high starch). Similarly, treatment with certain drugs, such as antibiotics, changing the source of sweeteners (fructose to sucrose - cane sugar; artificial sweeteners, etc.) or the fatty acid content of the feed, can lead to dramatic changes.

The point is that they are not there for free and by chance. We are now beginning to build a very different picture in which they play preponderant roles in our own lives. Many of the bacteria found appear to be involved in maintaining the body's homeostasis, regulate part of our immune responses, help keep harmful fatty acids at bay, generate signals involved in fat accumulation, keep pathogens at a non-hazardous level, regulate appetite, among other functions.

So far we are beginning to understand that the alteration of their populations is directly connected to the pandemics of obesity and diabetes that the whole world is facing. Just as you read it, obesity and all its sequels are connected to variations in microbiota, artificially induced by changes in diets and eating habits. The reason is not linked to the consumption of churritos (corn chips) in elementary schools, but to the increasingly accentuated tendency to a "healthy" diet that introduced alterations in the nutrients and signals that reach the microbiota.

We replaced cane sugar with fructose, xylans, and derivatives. We degrease everything we consume, we dispense with everything that "smells" of cholesterol - an indispensable metabolite. An example: we increase for no reason the consumption of dietary fiber, which came to us as part of fruit peels and vegetable fibers, and now we are forced to eat others provided in commercial products under the pretext that they will make us look a dream body, increase our intelligence and improve the brightness of our nails. We drink lactose-free and defatted milk - and even soy milk - because someone said they are healthier and now it turns out that we believe, without any proof, that we are all lactose intolerant.

Certain short-chain fatty acids, such as butyric acid, contained in whole milk and only in cow's milk, are indispensable in the immune response, so that doing without whole milk deprives us of them, altering in the process the microbiota that requires them.

Now it is fashionable a supposed therapy to "cleanse the intestine of impurities" by provoking diarrhea and applying vinegar enemas. Other practices are based on drinking pure or magnetized water and others are simply drinking distilled water at all hours - light - in little bottles that cost as much as the entire water tank and cistern of our house put together and that are useless. I have seen teenagers drink formulas designed for the cellular nutrition of kidney failure patients and buy them in stores without any control. Let it be understood, I am not calling for not bathing, not washing hands, much less binging on corn chips and fatty foods. The idea is that we must understand that our actions can further contribute to the alteration of our metagenomic structure and our status as metaorganisms with disastrous consequences. We cannot live in microbiologically pure environments.

The fight against obesity and diabetes cannot be based on a war against corn chips, but on the development of scientific research on our food in relation to our microbiota, on the knowledge of the microbiota of Mexicans by region, age, type of food, habits, etc. How can we make officials, doctors, shopkeepers, housewives and ourselves understand this?

Author: Horacio Cano Camacho, Research Professor at the Multidisciplinary Center for Biotechnology Studies, Faculty of Veterinary Medicine and Animal Husbandry, Universidad Michoacana. Source: Saber mas