At a time when the new novel by Michel Houellebecq, "Sérotonine", floods the storefronts of bookstores, a new study on depression, which will probably not benefit from the same media coverage, should soon appear in "The Medical Press" . Conducted by a team of researchers from Aix-Marseille University, it shows that the rate of depressions in France has increased from 6% in the 2000s to 8% in the 2010s.

"An increase of two points in ten years can not be by chance"comments one of the scientists involved, Guillaume Fond, a psychiatrist and public health doctor at the Marseille Hospital of Conception. In the line of sight: all the depressogenic factors that our environment and our way of life harbor. Stress, of course, but not only, warns the researcher. The poor quality of our diet would also play a leading role in this inexorable rise of depressive disorders. And this same diet could, if it were better chosen, prove instead a powerful ally in the fight against this disease, in addition to conventional antidepressant treatments.

Even if there is a saying that happiness is on the plate, the link between depression and diet is obviously not obvious to a non-specialist. The hyphen between the two is the immune system. More and more studies have shown in recent years that depression has a close link with this immune defense reaction that is inflammation (see opposite). "Modern food is more and more inflammatory"explains Guillaume Fond, because more and more rich in refined sugars and saturated fats, but also increasingly poor in metabolic regulation nutrients, such as vitamins or essential fatty acids, some of which have an anti-inflammatory effect .

In 2016, a study published in the American Journal of Psychiatry had demonstrated the beneficial effects on depression of at least three substances available in the form of dietary supplements: a family of fatty acids, omega-3s, and two vitamins, vitamin D and methylfolate (a form of vitamin B9). It has been proven that, taken in addition to an antidepressant, these nutrients reduce depressive symptoms. Yet, at least in France, psychiatrists are still rare in prescribing them systematically.

"There is still an idea in the minds that dietary supplements are 'soft medicine', not to say 'alternative medicine', regrets Guillaume Fond. For most people, taking vitamins is something that can not hurt, but it is not a treatment in itself. But our eyes change if we know that vitamin D is actually a hormone, and that it plays a role in the immune system and inflammatory reactions. "

Another class of food supplements with proven positive effects: probiotics, which promote in our intestinal flora the presence of "good" bacteria (while antibiotics kill the "bad"). In 2017, a first meta-analysis, having screened the results of half a dozen studies, concluded their effectiveness in adding to an antidepressant. A new meta-analysis, covering more than thirty studies but not yet published, will soon follow suit.

Neurons in the intestine

Even for their most convinced supporters, dietary supplements are not intended to replace antidepressants. Discovered by chance in the 1950s, these psychotropic drugs (which remain ineffective on about a third of patients) act on depression by increasing in the brain the amount of one or even, in some cases, two key neurotransmitters: serotonin, which has suggested his title to Michel Houellebecq, and norepinephrine (read below).

" Antidepressants overcome the deficiency of serotonin. What is needed, since this leads to a decrease in symptoms and therefore a better feeling for the patient. But they do not attack the root of the evil, that is to say, the cause of this deficit "explains the psychiatrist Marseille.

Now, 95% of the serotonin present in our body comes from … our belly! In recent decades, advances in biology have highlighted the existence and complex role of what is known as our "second brain" (and which is actually the first since it appeared earlier in evolution). Some 200 million neurons line the lining of a human's gut: the brain equivalent of a dog or cat. And these neurons of the enteric nervous system (to which are added 100,000 billion bacteria, ten times more than cells throughout our body!) Use, to communicate with each other, the same neurotransmitters as those of the central nervous system, in other words brain: serotonin, norepinephrine, dopamine … But they do not have the same role in the brain of "high" and in the "low": Messenger of the feeling of well-being above, serotonin, which ensures also the good functioning of our circadian clock serves, at the bottom, to rhythm the intestinal transit.

In the light of these discoveries, it is no longer surprising that the key to certain mental illnesses can be found in our gut. In fact, it appears that 90% of all known diseases are related to a microbiota disturbance, that this disturbance ranks on the side of causes or effects. Is it still reasonable to believe that mental illnesses could be an exception? And if that were the case, how could the strange results obtained by the "germ-free" studies carried out on rodents be explained? Several laboratory experiments have shown that mice born under sterile conditions, and thus deprived of the normal supply of bacteria, develop behavioral disorders that resemble psychiatric pathologies.

Diet, the composition of our microbiota, but also physical activity, all of which have an influence on our inflammatory status, should not be neglected in the treatment of depression. In many countries, these elements are part of the psychiatrist's "toolbox". France, in this respect, has incontestably a delay.

How antidepressants have been discovered

It is a good example of "serendipity", this fact, for a medical or scientific breakthrough, to have been carried out in a fortuitous way. Antidepressants may never have been discovered if, in sanatoria in the early 1950s, doctors did not realize that an anti-TB drug, isoniazid, had a positive effect on patients' moods. . Research has subsequently shown that isoniazid is an inhibitor – that is, it prevents the proper functioning – of an enzyme called monoamine oxidase. However, this enzyme itself has the function of degrading norepinephrine, serotonin and dopamine.

By blocking the enzyme, isoniazid therefore increases the amount of these three neurotransmitters in the brain. Thus, the two main families of antidepressants currently on the market have been progressively developed: selective serotonin reuptake inhibitors (SSRIs) which increase the level of this neurotransmitter in the brain; and mixed serotonin and norepinephrine reuptake inhibitors (SNRIs), which act on both neurotransmitters at the same time. Among the first, Prozac, Deroxat, Zoloft, Seropram, Seroplex … Among the latter, Effexor.

Acute or diffuse inflammation

One of the arguments put forward by psychiatrists to illustrate the link between depression and inflammation is that of "Disease behavior" ("Sickness behavior"): when a flu nails a person to bed and his body reacts with acute inflammation, this person has all the symptoms that are found chronically in depressions:

– she does not want anything;

– she has no appetite;

– she sleeps badly;

– she is irritable;

– it lacks energy;

– she has more pain, etc.

The idea-force of theimmuno-psychiatry is that, behind certain mental illnesses such as depression, hides a diffuse inflammation and low intensity, called "low grade", difficult to diagnose.

Yann Verdo

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