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Microbiota, the intestinal revolution. © INRA

Microbiota, the intestinal revolution

Feed your microbiota (2)


Updated on 04/25/2017
Published on 02/16/2017

City V countryside microbiota

The trend to keep babies and germs far from each other is a longstanding one. Improved hygiene, Caesarean births, and the overuse of antibiotics all keep bacteria at bay. The result? The microbiota of the very young is slow to develop and diversify. This can lead to difficulties when the immune system starts to mature, in turn causing health issues such as allergies. There have been many reports that support this hypothesis about the origin of allergies, known as the hygiene hypothesis. For example, children who live on farms, and who are therefore in contact with a more diversified environment in terms of bacteria, are less prone to allergies than children who live in cities. INRA researchers have also shown that mice bred in sterile conditions develop more severe allergies. Perhaps germs aren’t so bad after all!


. © Fotolia
© Fotolia

Microbiota: a good coach for immune defence

Pollen, peanuts, eggs, mites… allergies seem to be exploding in our modern societies, and the microbiota has something to do with it. But what exactly is the link between intestinal bacteria and these exaggerated reactions of the immune system? Science now knows that the microbiota plays a key role in a maturing immune system. It all begins at birth, when bacteria start to colonise a baby’s digestive tract. Thus begins a never-ending dialogue between microorganisms and the budding and inexperienced immune defences of a newborn. This is when the immune system learns to recognise the difference between good bacteria and dietary protein and the bad stuff. But it also learns to temper its reactions. Thanks to this rigorous training, immune response strikes the right balance.

Using fibre to fight allergies

Electron microscope image of a cross section of a mouse intestine at the colon.  The epithelium is tinted blue but contains, in green, mucus-producing cells. The green layer lining the inner surface of the epithelium is mucosa.. © Unai ESCRIBANO-VASQUEZ - Inra, ESCRIBANO-VASQUEZ Unai
Electron microscope image of a cross section of a mouse intestine at the colon. The epithelium is tinted blue but contains, in green, mucus-producing cells. The green layer lining the inner surface of the epithelium is mucosa. © Unai ESCRIBANO-VASQUEZ - Inra, ESCRIBANO-VASQUEZ Unai

Another factor, this time food-related, seems to link the microbiota with allergies. Western diets are increasingly poor in fibre. Dietary fibre is a form of polysaccharide that can only be broken down by bacteria in the intestines. When fibre is digested, it produces short-chain fatty acids (SCFAs), which enter the bloodstream. INRA researchers have found that SCFAs impact the immune system and serve as an anti-inflammatory. Mice which are fed a fibre-rich diet produce many SCFAs and are thereby less likely to develop pulmonary or food allergies. Therefore, a diet lacking in fibre combined with low exposure to bacteria seems to be a culprit in allowing allergies to gain ground in the modern world.

. © Fotolia

Gluten: friend or foe?

People who suffer from celiac disease cannot digest gluten properly. Thousands of other people claim to be intolerant to wheat protein. INRA researchers have turned their attention to the microbiota of consumers who bar bread and pasta from their diets. They have found, first and foremost, that people with a gluten-free diet suffer from a severe imbalance in their microbiota, with populations of good bacteria (bifidobacteria, lactobacilli) taking a nosedive. Indeed, these bacteria regularly feed on gluten. A gluten-free diet also means less fibre, which is also known to nourish the microbiota. The consequences of such dysbiosis* is an alteration in the production of short chain fatty acids (SCFAs), which have well-known beneficial effects on the immune system and cardiovascular health. A gluten-free diet does not, therefore, come at a small price. Why, then, do people who adopt one claim to feel better? Is banning gluten the real reason? Or do they feel better because reducing fibre intake also assuages some symptoms linked to digestion? The jury is still out on this question, and scientists continue to search for answers.

Vache. © INRA, NICOLAS Bertrand

Cows: gas factories

Where there are cows, there are microbiota. The microorganisms that populate the digestive tracts of cows are as vital as their heart or liver. Indeed, it is the microbiota that performs the biochemical feat of transforming a food as poor and indigestible as forage into energy and nutrients. The microbiota of cattle is particularly rich and diverse: in addition to bacteria, it is also made up of anaerobic fungi and protozoa, which pitch in to make digestion happen. Then there is another group of germs that has been a hot topic lately: methanogenic archaea* which, as their name suggests, produce methane during digestion. It just so happens that 14% of greenhouse gas emissions, which include methane, come from livestock rearing. That is why INRA researchers are taking a keen interest in the digestion of ruminants and the role methanogens play in the process.


The greener cows of tomorrow              

Methanogens kick in toward the end of digestion, producing methane from the substrata that other microorganisms provide. INRA researchers have found that the production of methane can be scaled back by 20% by adding lipids, in the form of linseed oil for example, to fodder. And this without affecting the well-being or productivity of cows. Lipids are toxic for some micro-organisms, including protozoa, and limiting protozoan populations has a direct effect on the activity of methanogens. And here’s another reason to love linseed oil: cows which consume it produce milk that is richer in omega-3s and other beneficial fatty acids. But scientists are not stopping there. Why not try and shape the microbiota from birth, in order to reduce methanogens? The goal is to achieve stable cow microbiota  that generate less greenhouse gas from the earliest days of a calf’s life. That way, cows would be as green as the pastures they graze upon.