TRUSTYOUR GUT

This “second brain” fuels your mind

It happens instantly when you have a moment of fear, a moment of shock or surprise—the cascade of activity across a crisscrossing network of 100 million neurons. Electrical signals and a surge of blood flow. But exactly which neurons are these? They’re the ones located in the walls of your digestive tract. They make up the gut’s “enteric nervous system,” which communicates constantly with your main brain.

GUT-BRAIN CONNECTION

We tend to think of the digestive tract and the brain as separate systems doing separate jobs for the body; but for decades, scientists have been studying how the brain in your head is closely connected to the “second brain” in your digestive tract.

What has brought new energy to this field in the past 10 years is the discovery that the trillions of “friendly” microbes residing in the gut—bacteria, but also potentially fungi and even viruses—can affect what happens in the brain.

The latest microbiota-gut-brain research supports the idea that gut health really matters to brain health. And, more importantly, it opens up new possibilities for controlling brain health through nutrition and a healthy lifestyle.

THE GUT-BRAIN CONVERSATION

For the most part, the brain is “sealed off” from the rest of the body by the blood-brain barrier. But, in fact, the gut and the brain have an ongoing dialogue.

The main two-way channel of direct gut-brain communication is the vagus nerve, a superhighway that runs between the central (brain and spinal cord) and enteric nervous systems. Yet it’s becoming clear that the micro-organisms residing in the gut also contribute to the messages that reach the brain.

Meghan Hockey, accredited practising dietitian and nutrition researcher in the Food & Mood Centre at Deakin University, Australia, says, “The gut and the brain are constantly talking to one another through microbial metabolites and immune, neuronal, and metabolic pathways.”

Microbes are known to affect messages to the brain in at least three ways:

1. They can directly stimulate the vagus nerve.

2. They can produce small molecules that escape the gut and circulate through the body to affect the brain.

3. They can cause changes in the immune cells of the gut, which causes a chain reaction in the immune system that eventually affects the brain.

DIFFERENT GUT BUGS, DIFFERENT BRAIN-RELATED CONDITIONS

Scientists are starting to uncover how the gut is connected to brain-related conditions. For example, individuals with major depressive disorder tend to have a different set of gut microbes than non-depressed individuals.

Different patterns in gut microbial communities have also been found in people with anxiety, schizophrenia, multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, and even in autism spectrum disorder.

While this doesn’t mean the gut microbes caused these conditions, it does mean that scientists can start looking at whether intervening at the distant site of the gut can affect how these conditions play out—or perhaps whether it’s possible to prevent the condition in the first place in susceptible individuals.

The influence of gut microbes is under investigation, too, in several conditions that are widely understood to be confined to the digestive tract: inflammatory bowel disease and irritable bowel syndrome.