Microbiome Overweight And Obesity – How To Reduce Risks By Targeting The Guts

Overweight and obesity affect 42.5% of the adult population. Excess weight is not the only characteristic of these conditions: both go hand in hand with changes in the population of microbes that live in the gut (the gut microbiota).

Not only that but alterations in the intestinal microbiota are also associated with an increased risk of complications typical of obesity, such as diabetes.

The microbiome analysis allows identifying intestinal microbiota and implementing strategies to correct those changes that increase the risks to health due to excess weight.

Gut Microbiome, Excess Weight And Obesity – A Surprising Relationship

The link between intestinal microbiota and obesity depends in part on the role played by the bacterial flora in regulating the energies taken with food.

The bacteria that live in the intestine are responsible for the fermentation of food components that otherwise would remain undigested. This fermentation increases the energy obtained from a meal, increasing it by 2 Kcal for each gram of fiber.

In itself, the fermentation of fibers is not a negative phenomenon; on the contrary, a diet rich in fiber promotes the growth of a health-friendly microbiota.


However, dysbiosis, the disruption to the microbiota homeostasis caused by an imbalance in the microflora, associated with excess weight, can lead obese people to absorb more energy than slim people.

Furthermore, the fermentation of fibers leads to short-chain fatty acids that inhibit the degradation of fats while stimulating their accumulation of triglycerides and the production of adipocytes (the cells of adipose tissue).

Obesity is a chronic, multifactorial pathology correlated to various pathologies:

  • Cardiovascular.
  • Metabolic.
  • Respiratory.
  • Osteoarticular.

In the onset of obesity, various factors interact in very complex behavioral, psychological, environmental, metabolic, and neuro-immuno-endocrine ways.

Gut Microbiome And Obesity


In recent years there has been an increase in studies and publications on the role of the intestinal microbiota in the pathogenesis of obesity.

Experimental and clinical evidence sheds surprising light on the complex entity of the intestinal microbiota and its multiple functions.

It has been observed that the microorganisms that colonize the gastrointestinal tract are not only almost inert hosts but are active protagonists of lively interactions between the gastrointestinal tract and the neuro-immuno-endocrine system.

The intestinal bacterial flora includes 1014 bacteria to which fungi and viruses are added. The overall genome of the intestinal bacterial flora alone is therefore exponentially richer in genes than the human genome.

Parents transmit only 1% of our genes; the remaining 99% are acquired by the microbiome present in the surrounding environment, particularly at the time of birth, during transit through the birth canal, and subsequently with breastfeeding.

The microbiome topic is so relevant that in the USA, the NHS is carrying out the Human Microbiome Project, a project with a total budget of 115 million dollars, which aims to identify and characterize microorganisms and their relationship with the state of human health and disease ( https://commonfund.nih.gov/hmp/index ).

It is, therefore, necessary to consider the substantial importance of the coexistence of the microbiota in our organism and to evaluate the dynamics of the microbiome, which is capable of transforming its gene expression concerning environmental factors, such as the type of diet and the state of health.

It has been observed that individuals of the same family have a similar core of classes and species of intestinal bacteria that can change according to the interactions with the host and with the environment.

Three main bacterial phyla are recognized in the average weight individual:

  • Firmicutes.
  • Actinobacteria.
  • Bacteroidetes.

Several studies have shown a relationship between gut microbiota and obesity. Although not unambiguously, studies carried out in both mice and humans have shown a modification in the intestinal microbiota composition in obese subjects with an increase in Firmicutes and a reduction in Bacteroidetes.

The microbiota can affect the body’s nutritional and metabolic balance by modulating the ability to extract energy from dietary foods and interacting with glycolipid metabolism.

The metabolites released by the fermentation of complex polysaccharides of the diet can increase glucose absorption, stimulate lipogenesis, modify the fatty acid composition of adipose tissue and liver, alter the permeability of the intestinal mucosal barrier, and alter the immune response.

Only through the complete typification of the bacterial species that colonize the gastrointestinal tract and the knowledge of their functions will it be possible to more accurately define a significant pathogenetic aspect of obesity and metabolic syndrome and prepare targeted therapeutic remedies.

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Microbiome And Complications Of Obesity

Alterations in the gut microbiota also affect the risk of health problems closely associated with obesity. The reduction of clostridia and the increase of lactobacilli are associated with insulin resistance, the entryway to diabetes.

The decrease in the richness of the microbiota is associated with both insulin resistance and an alteration in fat and cholesterol levels in the blood.

The communication between the intestine and the brain and the signals directed towards the adipose tissue is also altered by intestinal dysbiosis.

The changes in the gut flora typically associated with obesity alter the production of hormones and other molecules by the gut cells.

Characteristics Of The Microbiome Associated With Obesity

The main intestinal dysbiosis associated with obesity is the increased ratio of Firmicutes to Bacteroidetes. The other variations include:

  • Reduction of microbiome diversity.
  • Increase in the richness of the microbiome.
  • Increase in Blautia hydrogenotrophic, Coprococcus catus, Eubacterium ventriosum, Ruminococcus bromii, Ruminococcus obeum, Lactobacillus reuteri.
  • Reduction of Bacteroides faecichinchillae, Bacteroides thetaiotaomicron, Blautia wexlerae, Clostridium boltae, Flavonifractor plautii, Methanobrevibacter smithii, and various Bifidobacterium, Lactobacillus.

Can A Single Gut Bacterium Cause Obesity?


A particular type of bacterium that colonizes the intestinal tract could play a causal role in weight gain and obesity susceptibility: this is the researchers’ conclusion at Cedars-Sinai Medical Center in Los Angeles.

The authors’ hypothesis was based on previous observations in animal models in which the presence of methanogenic bacteria in the intestine can alter their metabolism and cause moderate weight gain. Furthermore, the methane levels in the exhalation of obese patients appear to be higher than in healthy subjects.

Briefly, in the study, the researchers used exhaled hydrogen and methane levels as a surrogate to establish the presence of the bacterium “Methanobrevibacter smithii” in the patients’ gastrointestinal tract. In total, 792 individuals were examined who were classified according to the exhaled levels of the two gases.

Following the statistical correction for age, the authors found that subjects who had high concentrations of both gases in their breath also had higher values ​​of the body mass index (BMI) and higher percentages of body fat.

According to the researchers, these observations could be explained by the influence of the activities of these bacteria on the assimilation of nutrients.

The study thus provided further evidence of a possible causal relationship between the composition of the so-called gut microbiome and the risk of developing body weight disorders.

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