From gut to brain: how fibre and the microbiome may influence brain health
Our gut and brain are in constant communication, yet how this so called gut brain axis works is still far from fully understood. Neuroscientist Esther Aarts studies how diet, gut bacteria and brain processes interact. On 19 May she will share her insights during the Young IFFI Event.
Aarts began her career in neurobiology, initially focusing on how the brain controls behaviour in relation to reward. “In my early research I mainly studied reward in the form of money,” she explains. During her postdoctoral research at the University of Berkeley, however, her focus shifted towards food. “Obesity was a major societal issue there. That led me to apply what I had learned about motivation, reward and control in the brain to eating behaviour.”
After returning to the Netherlands, her interest in the relationship between diet and the brain continued to grow. Today Aarts studies the bidirectional relationship between nutrition and brain function. “Food is not only fuel or building material for our brain. What we eat can also influence the brain through the gut.” Gut bacteria play a key role in this process. “The microbiome produces substances that affect the immune system and may also influence the brain.”
According to Aarts, this illustrates that the relationship between nutrition and brain health is broader than often assumed. Other systems also play a role, including the immune system and vascular health. “Diet can affect blood vessels, for example, which ultimately also influences the brain.”
Complex research
Research into the gut brain axis is complex. Many factors influence both gut health and brain processes, including stress, physical activity and lifestyle. There are also large individual differences in factors such as the microbiome and metabolism.
For that reason, the research group led by Aarts mainly focuses on understanding the underlying mechanisms. “We first try to determine which processes in the brain are involved.” Using brain imaging techniques, researchers can gain valuable insights even with relatively small groups of participants.
Communication between the gut and the brain occurs through several pathways. Gut bacteria produce metabolites that can influence the immune system and possibly also reach the brain. Another important route is the vagus nerve, which connects the central nervous system with the nervous system in the gut. Communication also works in the opposite direction. “Everyone knows that stress or nervousness can have an effect on the gut.”
The role of fibre
Dietary fibre plays an important role in research on the gut brain axis. Some fibres are fermentable and are therefore often referred to as prebiotic fibres. Humans cannot digest these fibres themselves, but gut bacteria convert them into short chain fatty acids such as butyrate.
“These substances are important for maintaining a healthy gut lining and they have anti inflammatory effects,” Aarts explains. As a result, they may indirectly influence the immune system. Animal studies also suggest that these metabolites may reach the brain. “That makes it interesting to investigate what those effects might be.”
In addition to fermentable fibres, other types of fibre also have health benefits. They can improve intestinal transit, contribute to satiety and help reduce cholesterol levels.
Fiber maxxing
The growing attention for fibre aligns with a consumer trend known as fiber maxxing, which refers to consciously increasing fibre intake. According to Aarts, this is in principle a positive development. “In the Netherlands most people do not consume enough fibre.”
At the same time, nuance is important. Not all fibres are suitable for everyone. Some fermentable fibres belong to the group known as FODMAPs and may cause symptoms in people with conditions such as irritable bowel syndrome, including bloating or abdominal pain. “That is why it is important to increase fibre intake gradually and to look at what works for each individual.”
Claims and future research
Although there is growing interest in the possible effects of fibre on brain health, firm conclusions are still difficult to draw. Observational studies show associations between a fibre rich diet and a lower risk of conditions such as depression or cognitive decline. However, well controlled intervention studies in humans are still limited. “Producers cannot currently make claims about the effects of fibre on brain health,” Aarts says. “More research is needed.”
In the coming years she expects research on the gut brain axis to deepen further. The focus is gradually shifting from identifying which bacteria are present to understanding what those bacteria actually do. New technologies also make it possible to measure changes in brain chemistry more precisely.
According to Aarts it is important that communication about nutrition and health remains nuanced. “Nutrition is not only about calories. It is also about fibre, vitamins and minerals and about what happens inside the body.”
The hope is that a better understanding of the gut brain axis will eventually contribute to more targeted dietary advice. “How we nourish our body also affects our brain. Hopefully in the future we will become more aware of that.”
Esther Aarts
Neuroscientist