Gut-brain health link reinforced as studies show food affects decisions, mental disorders

The enteric nervous system, simply put, is the nervous system within the gastrointestinal tract. It produces neurotransmitters as well as a large proportion of the “feel-good” hormone serotonin – also produced in the brain – and gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety.

An illustration showing how the gut and brain communicate via the vagus nerve. Illustration: Shutterstock

This is why psychiatrists are increasingly looking to the gut to help manage mental health disorders.

Dr Paul Clayton, a leading scientist in the field of nutrition, has been studying the gut-brain axis for decades. Photo: Dr Paul Clayton

The concept of the gut microbiome started to gain traction in scientific circles as far back as the late 1980s, says Dr Paul Clayton, a leader in the field of nutrition who has written several books, including Let Your Food Be Your Pharmaco-Nutrition: The New Road to Health, Healing and Happiness.

Dr Michael Gershon, a professor of pathology and cell biology at Columbia University in New York, and author of The Second Brain, says nerve cells in our gut can control its workings, and that this “brain” and the one in our head must cooperate.

Gershon’s work has encouraged generations of doctors and researchers to explore the link between the two.

Dr Michael Gershon is still working at the age of 86, having long examined the connection between the gastrointestinal tract and the brain. Photo: Columbia University

Scientists at Sorbonne University, in Paris, recently found the gut microbiome may affect decision making.

In a study, they added probiotics and prebiotics to the diets of participants for seven weeks to boost the good bacteria in their gut microbiomes, and had them play a game.

One player was given a sum of money to split however they liked with a second player, who was free to decline the offer if they deemed it unfair – in which case neither player received any money.

The good-bacteria boost was found to increase participants’ willingness to decline cash when they felt unfairly treated.

Research by scientists at the David Geffen School of Medicine at the University of California, Los Angeles, found evidence that the microbiomes of people who are highly mentally resilient differ from others.

The cover of Gershon’s book. Photo: Amazon

The authors of the study, published in the journal Nature, and which is believed to be the first of its kind, say that when stressed, we go into fight or flight mode, which can impair the brain’s “braking system”.

The participants in the study who were able to apply emotional and cognitive “brakes” and keep a level head in stressful situations were found to have healthier guts.

Their microbiomes had less inflammation and better gut-barrier integrity, which protects against leaky gut, a condition that compromises the gut barrier’s ability to absorb nutrients and block toxins from entering the gut.

Some doctors hypothesise leaky gut syndrome may contribute to depression and other mental health disorders.

Clayton says modern diets are often deficient in prebiotic fibre – that which is not digestible but can help good bacteria grow in the gut. A lack of prebiotic fibre upsets the balance in the microbiome, leading to chronic inflammatory stress in the gut wall – and leaky gut.

This in turn triggers inflammation of the nervous tissue, which has multiple negative effects, Clayton says.

Modern diets are deficient in prebiotic fibre – found in certain grains, seeds, fruits and vegetables – according to Clayton. This upsets the balance in the microbiome, which can lead to leaky gut syndrome. Photo: Shutterstock

In the short term it can lead to anxiety, depression, reduced impulse control and social withdrawal. In the longer term it can even lead to an increased risk of neurodegenerative diseases.

What we eat can also affect our thinking and our mood, and can even reduce the risks associated with illnesses that affect our brains.

The keto diet – in which only about 10 per cent of calories are consumed in the form of carbohydrates, 30 per cent from protein and 60 per cent from fat – provides an alternative fuel for the brain, shifting the body’s main energy source from glucose to fat in a process known as ketosis.

This is believed to help quieten the brain’s neurological actions and also reduce inflammation and oxidative stress.

A century ago, American doctor Russell Morse Wilder designed what was in essence the first ketogenic diet to treat epilepsy. It had already been found that fasting helped control seizures, but perpetual fasting is, of course, unsustainable. So Wilder came up with a low-carb, high-fat, high-protein diet as an alternative.

Dozens of studies have since shown the efficacy of the keto diet in epilepsy management. Several found it made a significant difference in about 70 per cent of participants in just three months.

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