Fiber benefits health in many ways—from weight management to reducing the risk of diabetes, heart disease, and certain types of cancer.
But what about its effects on emotions and brain health?
Fiber and Gut Microbiota
Primarily found in fruits, vegetables, whole grains, nuts, and legumes, fiber enhances the richness and diversity of the gut microbiota. Known as prebiotics, they serve as food for beneficial bacteria that colonize the gut. And what exactly do these gut bacteria do? When properly nourished, they produce chemical molecules that are beneficial to health. One such molecule is butyrate, a valuable metabolite that helps control inflammation. It is well established that many emotional and mental imbalances, such as depression, are associated with inflammation in the body.
Gut-Brain Axis
About 200 million neurons form a complex network surrounding the walls of our intestines, hence the nickname “second brain.” This neural network, called the enteric nervous system, plays a role in digestion, of course, but also influences the brain through several pathways that researchers are only beginning to unravel.
A Two-Way Network
This gut-brain neurological network is bidirectional. It allows the brain to influence the motor, sensory, and secretory activities of the digestive tract and, conversely, enables the gut to affect brain functions. Notably, communication from gut neurons to the brain is said to be seven times more significant than in the opposite direction, highlighting the impressive role of the gut microbiota. This long-distance interaction can occur through neurotransmitters—those tiny chemical messengers released by neurons.
Bacterial Flora and Neurotransmitters
It is estimated that 80% of neurotransmitters are generated by the microbiota. Serotonin, 95% of which is produced by the enteric nervous system, is a neurotransmitter that regulates intestinal transit and the immune system. However, part of it reaches the brain, particularly the hypothalamus, which helps manage our emotions.
Candida, Streptococcus, Escherichia, and Enterococcus are reported to produce serotonin, while various species of Bacillus and Escherichia secrete dopamine, acetylcholine, and norepinephrine. Bifidobacterium infantis increases serum levels of tryptophan, a precursor to serotonin. Lactobacillus and Bifidobacterium are involved in the production of GABA, the main calming neurotransmitter. This is how gut neurons play a role in managing our emotions.
Fiber Diversity
Eric Martens, a researcher at the University of Michigan Medical School who leads a lab on gut microbiota and nutrition, states: “Of all the different nutrients we consume, fiber is the only component of our diet that directly feeds our gut microbiota.”
It has also been shown that consuming a wide variety of fiber sources is likely better than consuming just one type. A more diverse diet, including various molecules from different sources, results in a more balanced, rich, and diverse gut microbiota.
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