Gut instinct: the gut-brain connection explained

Posted on 20 August 2018

An intimately connected highway runs between our brain and gut, and the hormones generated in both these organs, which travel this biological highway, play a large role in dictating our emotions.

It’s a two-way highway, explains neurologist Dr Stella de Kock. Cells in our brain excrete hormones that affect our gut, and cells in our gut excrete hormones that affect the brain, and so too our moods. The microbiome in our gut, the bacterial makeup, in other words, is arguably the most important in determining the health of this two-way communication system, she explains.

Healthy gut, happy mind

Essentially, a healthy microbiome in the gut creates the necessary amount of the amino acid tryptophan, which is the building block of serotonin, that all-important biochemical that decides our moods. Serotonin is a key neurotransmitter between the brain and gastrointestinal tract, according to scientists in the paper, Serotonin, Tryptophan Metabolism and the Brain-gut-microbiome Axis. “Accumulating evidence points to a critical role for the gut microbiome in regulating normal functioning of this axis,” the authors say.

Considering that 85% of the serotonin in the human body originates in the gastrointestinal tract, according to De Kock, it’s quite evident we should be taking great care of what we put into our gut and how we keep this microbiome happy. Speaking in a podcast hosted by the American Biome Institute, Dr Erica Sonnenburg says we should include foods in our diet that are not necessarily meant to be digested by our native enzymes, “but rather ones that are destined to provide nutrition for the bacteria that live inside us.”

What to eat

Fibre is a good example of a plant-based material that is indigestible and is actually broken down into important metabolites by the bacteria in our gut.

Good for our microbiome:

  • Non-preservatives
  • fruit and vegetables
  • A varied diet of foods from the different food groups

The bad:

  • Excessive sugar intake
  • Trans fats (found in fried foods, creamers and margarines amongst others.)

There’s a good chance you’re killing the healthy bacteria in your gastrointestinal tract if you eat preservative-laden foods every day, says De Kock, which may lead to lower levels of serotonin. This, in turn, can lead to anxiety and mood fluctuations.

Foods rich in tryptophan:

  • Eggs
  • Oats
  • Lentils
  • Red meat
  • Salmon

“The gut is your second brain,” says De Kock, and explains that people with irritable bowel syndrome also often suffer from anxiety. The two are linked. Moreover, “When we target anxiety and depression with anti-depressants, it’s assumed we target the brain, but these medications target the gut as well,” she explains.

Whether imbalances in this bio highway can lead to clinical depression in humans is still a matter of scientific speculation, but tests on mice and rats have proven that there may indeed be a link, notes De Kock.


Published in Gastroenterology

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