Understanding how the gut microbiome interacts with the brain could open new avenues for slowing the progression of multiple sclerosis (MS), promoting nerve cell repair, and improving patients’ quality of life.
Could one of the keys to fighting multiple sclerosis lie within the gut? For several years, scientists working to better understand this disease – characterized by the destruction of myelin, the protective sheath around nerve fibers – have shown increasing interest in the digestive system.
It has been discovered that the gut microbiome – the collection of trillions of bacteria that colonize our intestines – plays a key role in inflammation and neuronal repair. These microbes produce molecules that intervene at different levels in the body: they regulate immune cells, such as T lymphocytes, support cells responsible for forming the myelin sheath, and even influence the circadian rhythm (sleep-wake cycle) and the drainage of cerebral waste, which must be eliminated to maintain a healthy brain environment.
These diverse interactions help limit autoimmune reactions, which are at the root of multiple sclerosis.
The Causes of Multiple Sclerosis Are Still Under Investigation
Multiple sclerosis is a chronic disease of the central nervous system (brain and spinal cord) in which the immune system attacks the myelin, the protective sheath around neurons, generating plaque-like lesions, hence the name of the disease. This destruction leads to varied symptoms: fatigue, motor, sensory, cognitive, sphincter, or visual disturbances.
The disease can evolve in relapses (known as relapsing-remitting form, which represents 85% of cases at the beginning of the disease) or progressively.
Historically, multiple sclerosis has been considered to result from complex interactions between the immune system and the nervous system. Being a multifactorial disease, it is the result of the combination of an individual genetic predisposition and environmental factors, such as the Epstein-Barr virus (responsible for mononucleosis), vitamin D deficiency, obesity, tobacco consumption, and intestinal inflammation. In recent years, major interest has been given to the contribution of the gut to the development of this disease.
The Microbiome, a Regulator of Immunity
The human gut harbors more than 100 trillion bacteria spread over an area of 250 to 400 square meters – up to 10 times more than all the cells that make up our body. These microbes perform several functions, including:
- Protecting the gut against infections;
- Helping to digest certain foods;
- Producing vitamins and useful molecules (vitamin K, B vitamins, short-chain fatty acids…);
- Regulating the immune system.
The gut microbiome interacts, for example, with lymphocytes, cells that play a central role in immunity. Some bacterial profiles promote the maturation of lymphocytes favoring inflammation (such as Th17 lymphocytes), while others induce immunological tolerance (by promoting the expansion of regulatory T lymphocytes).
These interactions help limit autoimmune reactions (reactions in which the immune system attacks the body it is supposed to defend) and protect the brain.
The gut microbiome also modulates the activity of microglia, astrocytes, and oligodendrocytes, families of cells that play a key role in the defense and repair of the brain.
Microbiome Imbalance and Multiple Sclerosis
In patients with multiple sclerosis (MS), in both its relapsing and progressive forms, the microbiome is imbalanced, a condition known as “dysbiosis.” Here’s characterized by a decrease in populations of beneficial bacteria (Firmicutes, Bifidobacterium, Coprococcus, Roseburia…) and an increase in pro-inflammatory bacteria (Bacteroidetes, Akkermansia, Ruminococcus…).
This dysbiosis leads to a decrease in the production of short-chain fatty acids. These molecules are essential for balancing the various subtypes of lymphocytes in the immune system. Some short-chain fatty acids produced by the microbiome cross the blood-brain barrier and reach the central nervous system, where they limit inflammation by favoring regulatory T lymphocytes and inhibiting Th17 lymphocytes, which are responsible for producing pro-inflammatory cytokines. They thus contribute to the integrity of the brain’s protective barrier.
These metabolites are also important for the proper development and functioning of cells that produce myelin (oligodendrocytes necessary for repairing the sheath around neurons). A recent study showed that an imbalance in these molecules blocks the differentiation and maturation of myelin-producing cells, preventing remyelination.
Certain metabolites also regulate the activity of “support” cells of the brain essential for its proper functioning (astrocytes and microglia). In doing so, they reduce the production of inflammatory molecules and limit neuronal damage.
Conversely, some molecules produced by pro-inflammatory bacteria accelerate myelin destruction and perpetuate chronic inflammation.
Research has also shown that the composition of the microbiome has an impact on the regulation of the circadian rhythm, the body’s internal clock. Patients with a more diverse microbiome often have better sleep. The proper regulation of this internal clock and the restructuring of immunological and metabolic rhythms may help counteract disease progression.
the gut acts as a true conductor, modulating immunity, inflammation, and nerve repair, and influencing the severity and evolution of multiple sclerosis.
Diet: Mediterranean Diet and Vitamin D
Diet shapes the microbiome and the inflammatory state of the body. Adopting a Mediterranean diet – rich in fruits, vegetables, legumes, whole grains, fish, vegetable oils, and low in saturated fats – which is anti-inflammatory, is beneficial for people with multiple sclerosis.
This diet provides fiber and antioxidants that nourish “good” bacteria and promote the production of short-chain fatty acids, limiting inflammation and supporting remyelinating cells. This type of diet is associated with less fatigue, better quality of life, and a possible reduction in relapses.
Vitamin D complements these effects: it regulates T lymphocytes, limits inflammation, and slows disease activity. The French study “D Lay MS” showed that high-dose vitamin D supplementation reduces the appearance of new lesions and prolongs the time before the reappearance of multiple sclerosis symptoms, while remaining well tolerated.
Diet and vitamin D are therefore concrete levers for acting on the microbiome, immune balance, and repair of the central nervous system in the context of multiple sclerosis. Various therapeutic approaches based on microbiome modulation are also being added to these interventions.
The evaluation of the potential benefits of microbiome modulation in addition to conventional MS treatments is the subject of various studies. For example, propionate supplementation (500 mg twice a day) has been associated with fewer relapses and stabilization of disability.
Beyond restoring the microbiome via diet, approaches such as the use of prebiotics, probiotics, or microbiome restoration are also being studied. Its direct impact on stimulating remyelination is currently being studied.
Effects That Also Play on Quality of Life
The microbiome influences patients’ daily lives, affecting their level of fatigue, sleep, digestion, and recovery after relapses. In consultation, we routinely discuss this topic from the time of diagnosis to provide comprehensive care to patients. Some practical tips to remember:
- Adopt a fiber-rich diet close to the Mediterranean model;
- Reduce consumption of pro-inflammatory foods, i.e., foods rich in animal saturated fats, highly processed, very sugary, or very spicy: processed meats, cheeses, creams…;
- Maintain a regular sleep schedule and engage in appropriate physical activity;
- Reduce stress and avoid tobacco or excessive alcohol consumption.
Of course, these measures do not replace medical treatments, but they improve well-being, rebalance immunity, and may help slow disease progression.
a growing body of evidence shows that in the case of multiple sclerosis, the gut and brain are closely linked. Promoting the establishment and maintenance of a diversified microbiome allows modulating inflammation, the survival of myelin-producing cells, and the proper balance of the immune system, while having a positive influence on sleep, recovery, and daily available energy.
This approach, integrated with conventional treatments, constitutes for clinicians a means of slowing the progression of the disease, reducing the resulting disabilities, and improving the quality of life of patients with multiple sclerosis.
This article is published as part of the Brain Week, which will be held from March 16 to 22, 2026.
