Long confined to their role in digestion, dietary fibers today reveal a much broader potential. According to numerous recent studies, they also play a central role… in protecting the brain and in particular slowing down age-related cognitive decline. A close link which can be explained by a fascinating interaction between our diet, our intestinal microbiota and our brain. Explanations.
A nutrient still largely under-consumed
Whole grains, fruits, vegetables, legumes, nuts or seeds: these fiber-rich foods should form the basis of our daily diet. However, let’s face it, the reality is quite different. In most Western countries, an overwhelming majority of the population does not even reach half of the recommended intakes.
However, increasing your fiber consumption is considered one of the most powerful nutritional levers for overall health. “A diet rich in fiber should be seen as essential.says John Cummings, Emeritus Professor of Gastroenterology for the BBC. The data speaks for itself: people who consume the most have a 15 to 30% reduced risk of mortality, as well as a lower risk of cardiovascular disease, type 2 diabetes and certain cancers. And that, strictly speaking, we already knew.
Fibers and brain: the key role of the gut-brain axis
But what is particularly interesting to researchers today is the impact of fibers on cognitive health. According to Karen Scott, professor of gut microbiology at the University of Aberdeen, “Increasing your fiber intake is one of the most beneficial dietary changes for the brain”.
The explanation lies in the gut-brain axis, a two-way communication system between our digestive system and our central nervous system. Fiber, which is not digested in the small intestine, arrives intact in the colon where it serves as food for intestinal bacteria.
The microbiota, conductor of cognitive protection
It is precisely this mechanism that Orlane Fagnoni, dietitian-nutritionist for True Medical, details: “Dietary fiber is not only beneficial for digestion. It also plays a protective role at the neuronal level, by slowing certain signs of cognitive decline”she explains.
How ? When gut bacteria ferment fiber, they produce short-chain fatty acids — including butyrate, propionate and acetate. These compounds have powerful anti-inflammatory effects and directly influence brain activity.
“Chronic inflammation is one of the major factors in cognitive decline. However, fatty acids from fiber fermentation help to reduce this inflammation”notes our expert. Result: an environment more favorable to the proper functioning of the brain.
More and more convincing studies
Scientific data confirms this relationship. A large 2022 study of more than 3,700 adults showed that high fiber intake was associated with a lower risk of dementia. Other work carried out in people over 60 also reveals better cognitive performance in those whose diet is richest in fiber.
Even more recently, a randomized controlled trial carried out in twins made it possible to go further. Participants who consumed prebiotic fiber daily for three months performed better on cognitive tests than those who received a placebo. Analysis of their microbiota showed an increase in beneficial bacteria like
Bifidobacterium.
These results reinforce the idea of a causal link between fibers, microbiota and cognition. All the data converges towards a clear conclusion: a microbiota depleted in fiber could weaken the brain with age.
How can you actually increase your fiber intake?
If fibers do not, however, constitute a “miracle” solution on their own, they are fully part of a global prevention strategy. “The idea is not to change everything overnight, but to gradually increase intake in a diet focused on well-being”recalls Orlane Fagnoni.
A few simple tips can help you:
- Aim for at least five fruits and vegetables per day, or even more;
- Include legumes regularly (ideally three times a week or more);
- Gradually replace refined starchy foods with whole foods;
- Vary sources: fruits, vegetables, whole grains, nuts, seeds, legumes;
- Choose snacks rich in fiber such as apples, plain popcorn, nuts or seeds.
For certain people, particularly the elderly or those suffering from chewing disorders, fiber supplements can also provide occasional help.