Gut microbiota info

Everything you always wanted to know about the gut microbiota…

The word microbiota represents an ensemble of microorganisms that resides in a previously established environment. Human beings have clusters of bacteria in different parts of the body, such as in the surface or deep layers of skin (skin microbiota), the mouth (oral microbiota), the vagina (vaginal microbiota), and so on.

About Gut MicrobiotaGut microbiota (formerly called gut flora) is the name given today to the microbe population living in our intestine

Our gut microbiota contains tens of trillions of microorganisms, including at least 1000 different species of known bacteria with more than 3 million genes (150 times more than human genes). Microbiota can, in total, weigh up to 2 kg. One third of our gut microbiota is common to most people, while two thirds are specific to each one of us. In other words, the microbiota in your intestine is like an individual identity card.

As its name states, gut microbiota is harboured in the intestine, one of the main areas in our bodies that comes into contact with the external environment (other examples are the skin and the lungs).

Why is the gut microbiota importantWhile each of us has a unique microbiota, it always fullfils the same physiological functions, with direct impact on our health

Some of the functions are:

  • It helps the body to digest certain foods that the stomach and small intestine have not been able to digest.
  • It helps with the production of some vitamins (B and K).
  • It helps us combat aggressions from other microorganisms, maintaining the wholeness of the intestinal mucosa.
  • It plays an important role in the immune system, performing a barrier effect.
  • A healthy and balanced gut microbiota is key to ensuring proper digestive functioning.

Taking into account the major role gut microbiota plays in the normal functioning of the body and the different functions it accomplishes, experts nowadays consider it as an “organ”. However, it is an “acquired” organ, as babies are born sterile; that is, intestine colonisation starts right after birth and evolves as we grow.

WHEN does gut microbiota start developing?The development of gut microbiota starts at birth

The newborn’s digestive tract is quickly colonised by microorganisms from the mother (vaginal, faecal, skin, breast, etc.), the environment in which the delivery takes place, the air, etc. From the third day, the composition of the intestinal flora is directly dependent on how the infant is fed: breastfed babies’ gut microbiota, for example, is mainly dominated by Bifidobacteria, compared to babies nourished with infant formulas. Scientists consider that by the age of 3, microbiota becomes stable and similar to that of adults, continuing its evolution at a stadier rate throughout life.

HOW does gut microbiota evolve?The composition of our microbiota evolves throughout our entire life, from birth to old age, and is the result of different environmental influences

Gut microbiota’s balance can be affected during the ageing process and, consequently, the elderly have substantially different microbiota to younger adults.

While the general composition of the intestinal microbiota is similar in most healthy people, the species composition is highly personalised and largely determined by our environment and our diet. The composition of gut microbiota may become accustomed to dietary components, either temporarily or permanently. Japanese people, for example, can digest seaweeds (part of their daily diet) thanks to specific enzymes that their microbiota has acquired from marine bacteria.

Although it can adapt to change, a loss of balance in gut microbiota may arise in some specific situations. This is called dysbiosis. Dysbiosis may be linked to health problems such as functional bowel disorders, inflammatory bowel disease, allergies, obesity and diabetes.

Many studies have demonstrated the beneficial effects of prebiotics and probiotics on our gut microbiota. Serving as “food” for beneficial bacteria, prebiotics help improve the functioning of microbiota while allowing the growth and activity of some “good” bacteria. Present in some fermented products such as yoghourt, probiotics help gut microbiota keep its balance, integrity and diversity.

Thanks to technological progress, the picture of the bacteria living in the gastrointestinal tract is becoming clearer. Researchers now use a range of techniques, including the tools derived from molecular biology, to further clarify the mysteries of microbiota. While there are still some things that are yet to be discovered, more and more findings are being presented every day.

Gut microbiota key data and figuresGut microbiota plays an important role in our lives and in the way our bodies function

  • Gut microbiota plays an important role in our lives and in the way our bodies function.
  • The composition of gut microbiota is unique to each individual, just like our fingerprints.
  • Our gut microbiota contains tens of trillions of bacteria – ten times more cells than in our body.
  • There are more than 3 millions microbial genes in our gut microbiota –150 times more genes than in the human genome.
  • Microbiota, in total, can weigh up to 2 kg.
  • More than 1,000 different known bacterial species can be found in human gut microbiota, but only 150 to 170 predominate in any given subject.

Diet & Gut microbiota

The influence of diet on gut microbiota

The food we eat plays an essential role in maintaining the diversity and proper functioning of our gut microbiota.
When talking about gut microbiota, it could be said that “we are what we eat“, as what we consume also feeds off the hundreds of trillions of bacteria living in our digestive system. For this reason, a varied and balanced diet is essential.

The food we eat plays an essential role in maintaining the diversity and proper functioning of our gut microbiota

Prebiotics and probiotics are two of the most widely studied elements in the field of gut microbiota. Both have effects that are considered beneficial for the gut microbiota which impacts various functions of the body such as the digestive condition, for this reason, specialists highlight the importance of including both of them in our diet, in order to promote a healthy microbiota.


The concept of the prebiotics, sometimes called fermentable fibre, was initially introduced in 1995 by Gibson and Roberfroid. It is defined as the indigestible ingredients in food that selectively promote the growth and activity of a limited number of autochthonous bacterial species, and thus conferring a benefit for the host1. Prebiotics can be found naturally in food or added to them (functional products).

Prebiotics are naturally present in vegetables and fruit such as garlic, onions, leeks, asparagus, artichokes, tomatoes, bananas, plums and apples; in grains and cereals like bran, and in nuts like almonds. For this reason, vegetables, fruits and cereals should be part of a balanced and healthy diet.

As in many other fields, balance and variety are essential when eating prebiotic foods. Although a fibre-rich diet benefits gut bacteria, excess fibre may lead to discomfort or abdominal bloating in some people.

For further information on prebiotics, why not check out this information sheet from the International Scientific Association for Probiotics and Prebiotics – ISAPP.


The World Health Organization defines2 probiotics as live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.

These microorganisms partially resist to the digestion process, alongside to the progression in the digestive system. They provide a range of benefits for the body, including the maintenance of digestive comfort and the regulation of the immune system. Probiotics can also help balance the gut microbiota when it has been affected by poor diet, infections, some antibiotics treatments or other external factors such as stress3.
Many probiotics come from bacteria traditionally used for fermenting food. At the present time, a large number of relevant (well-designed) clinical trials with probiotics have been performed and the most common probiotics studied belong to two genera, Lactobacillus and Bifidobacterium, but other microorganisms including Enterococcus and Streptococcus, among others, have been also studied.

Studies have shown that probiotics help maintain digestive health (through different mechanisms), and that is why experts4 agree that they can be considered as probiotics5. Some of these bacterial species can also be found in a range of foods (such as yogurts and fermented milks) or supplements.
For further information on probiotics, why not check out this information sheet from the International Scientific Association for Probiotics and Prebiotics – ISAPP or the World Gastroenterology Organisation Global Guidelines on Probiotics and Prebiotics.

1 Gibson GR, Roberfroid MB. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J Nutr. 1995 Jun;125(6):1401-12. PMID

2 Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria, Report of a Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria, Cordoba, Argentina, October 1-4,200

3 Moheb Costandi, Microbes on Your Mind, Scientific American Mind 23, 32 (2012).