Chronicles

If we were asked in what way does exercise affect our body, most of us would immediately picture the muscles, and how the arms and legs of athletes and gym lovers look bulky, toned and beefy. It is obvious that exercise has an impact on the muscular system, but the benefits of exercise extend much over this, influencing the function of almost all the organs in our body.

One element that may be positively modified by physical exercise and through which it could promote well-being is the gut microbiota. The human microbiota is the collection of microbes that live on and in our body, with the largest and most diverse cluster living in our intestines. It has been estimated that the number of organisms composing the entire human microbiota is 10 times larger than the total number of cells in the human body. Besides the impressive number, the composition of this microbiota is also very diverse. Fungi, viruses, parasites and over 2000 different species of bacteria inhabit the adult human gut, and this composition determines the health of the host, which means…us!

Humans and their microbiota have a symbiotic relationship, which means that they work together, work for each other, benefit each other, and depend on each other for survival. The host provides to the microbiota a stable environment to inhabit and nutrients from the diet. In turn, the microbiota is responsible for digesting complex carbohydrates that our gut enzymes cannot break down for absorption.

These complex carbohydrates, for instance the fibers from different plants, are metabolized by the microbiota into products that can be used by other organs like the liver, to produce energy. These products are called Short-Chain Fatty Acids (SCFAs) and some of them also help in maintaining the function of the intestinal cells and the integrity of the intestinal wall. The intestinal wall is a natural barrier which prevents harmful bacteria and their toxins from entering into the bloodstream and disseminate throughout the body.

Even in a healthy state, some of the microorganisms that compose our gut microbiota are pathogens and can cause damage to the body. If these toxic organisms have access to the bloodstream, they can induce infection and inflammation in different organs. That is why preserving a healthy microbiota is paramount to prevent any leakage and preserve a normal intestinal permeability. The composition of the microbiome appears to be specific to the host, with very high variability between individuals and at the same time, remarkably susceptible to change throughout the life of a person.

Some of the factors that influence this composition are difficult or impossible to change, for instance age, geographical origin or whether you were born by vaginal or cesarean birth. Other environmental stimuli however, can be modified, for instance our dietary habits or the routine of physical activity that we follow. Our dietary and nutritional patterns have a big influence on the composition of our microbiota and on its health. Recent studies indicate that the diet of individuals strongly influence the development of an aberrant microbiome, which, in turn may affect intestinal barrier function and promote metabolic disorders.

The consumption of diets high in refined sugars such as fructose present in sweetened beverages or juices has the potential of breaking the symbiotic relationship between microbes and the host. This state, called dysbiosis, changes the composition of the gut microbiota, which might no longer produce enough SCFAs and thus, can no longer protect the intestinal wall. A diet high in fats has also been shown to have detrimental effects on the composition of the gut microbiota and its symbiotic relationship with the host.

This adverse effect of high-fat and high-sugar diets on our health add to the list of metabolic abnormalities they cause on several other organs such as the pancreas, inducing Type 2 Diabetes, or the liver, inducing Non-Alcoholic Fatty Liver Disease (NAFLD). The liver is highly exposed to the substances that come from the gut, forming together with the gut what is known as the Gut-Liver Axis. Once the nutrients from inside the gut, including SCFAs, are absorbed into the bloodstream, they travel directly to the liver, where they can be metabolized.

A perturbation in the relationship between the host and the microbial population in the intestine and the consequential leaking gut, render the liver exposed to all kind of toxic substances that can cause inflammation. This is particularly dangerous in situations where the normal function or state of the liver is already compromised, as is the case in NAFLD. In the early stages of NAFLD, there is an excessive accumulation of fat inside the liver cells that put them at risk for malfunction.

The harmful toxins that reach the liver can prompt an inflammation in these cells, which are more susceptible than the cells of the normal liver. This complicates the disease of NAFLD, aggravating it. On the other hand, as much as in the other organs affected by metabolic diseases, a healthy diet and exercise have beneficial effects on the gut microbiota. Regular and moderate exercise training improve the diversity of the gut microbial population.

Researchers have found that physical activity, even independently of diet, alters the composition of gut microbiota in a way that increases the production of SCFAs and that is beneficial for health. So, if you want a healthy gut environment, eat well and move more, this will keep your microbiota happy.

Authors: Getachew Debas Belew and Sravan Balloji are early stage researchers of the FOIE GRAS project. Getachew Debas Belew is doing his research at the Center for Neuroscience and Cell Biology (CNC), at the University of Coimbra (Portugal), at the Università degli studi di Bari Aldo Moro (UNIBA), in Bari (Italy), and at CNR (Italy). Sravan Balloji is doing his research at the Instituto de Investigaciones Biomédicas de Barcelona (IIBB-CSIC), in Barcelona (Spain), at the Helmholtz Zentrum Muenchen Deutsches Forschungszentrum Fuer Gesundheit Und Umwelt GMBH (HMUG), in Muenchen (Germany), and at the CNC, in Coimbra (Portugal).

The project: This chronicle results from the collaboration between the Center for Neuroscience and Cell Biology (CNC) of the University of Coimbra, the European Training Network FOIE GRAS (http://www.projectfoiegras.eu), the Erasmus+ Program and the Academic Sports Federation University (FADU) in the scope of the European University Games Coimbra 2018.

Coordination: Anabela Marisa Azul, João Ramalho-Santos, Mireia Alemany i Pagès, Paulo Oliveira and Sara Varela Amaral

Revision of the text: Mireia Alemany i Pagès, Anabela Marisa Azul, John Jones, João Ramalho-Santos, Piero Portincasa, Carina Prip-Buus, Paula Macedo, Juan Catafau, Carlos Palmeira, Hans Zischka and Paulo Jorge Oliveira.

Illustration: Rui Tavares

This chronicle reflects only the authors’ views and the Commission is not responsible for any use that may be made of the information it contains.