Understanding The Gut Brain Connection: The Relationship between Food and Mood

You may have heard the gut or, more specifically, the Enteric Nervous System, referred to as the second brain. The ENS is the most complex neural network outside the brain, controlling various digestive functions and operating autonomously from the central nervous system.

The gut microbiome interacts with the brain using neural, inflammatory, and hormonal signalling pathways. Various research has found the ingestion of probiotics in healthy individuals, which theoretically target the gut microbiome, to alter the brain’s response to tasks requiring emotional attention. As the composition of gut microbiota, influenced by diet, impacts the production of neurotransmitters and inflammation within the body, it tracks that the food we eat can significantly impact our mood. 

How Food Affects Our Mood

Serotonin, the neurotransmitter involved in mood regulation, is commonly associated with the brain, however roughly 95% of serotonin is produced in the gastrointestinal tract. The biosynthesis of serotonin begins with the amino acid tryptophan, an essential amino acid obtained through the diet. Tryptophan competes with other amino acids to cross the blood-brain barrier, and so factors such as protein intake can affect the amount of tryptophan that reaches the brain. 

Certain foods, like poultry, nuts and seeds, contain higher levels of tryptophan, so consuming these foods has the potential to increase serotonin levels. Similarly, carbohydrates can enhance the uptake of tryptophan to the brain through the release of insulin, which reduces the levels of competing amino acids in the bloodstream.

Around 50% of dopamine, the neurotransmitter associated with pleasure, reward, and motivation, is produced in the gut. Dopamine produced and released in the gut does not cross the blood-brain barrier in significant amounts. However, gut-derived dopamine can influence mood indirectly through the gut-brain axis.

The Right Type of Diet 

Observational studies have shown individuals with depression to score significantly higher in dietary inflammation, characterised by a greater consumption of foods including trans fats and refined carbohydrates and lower intake of nutritional foods thought to have anti-inflammatory properties.

The Mediterranean diet is characterised as anti-inflammatory, high in fibre, polyphenols and unsaturated fatty acids which can promote the gut microbial taxa, metabolising these food sources into anti-inflammatory metabolites. Our mental health can also be impacted by nutrient deficiencies, as inadequate intake of vitamins and minerals can affect the synthesis and function of neurotransmitters. Deficiencies in B vitamins, such as B12 and folate, for example, have been linked to increased risk of depression. 

Foods with a high glycaemic index, such as sugary snacks and refined carbohydrates, can lead to rapid spikes and crashes in blood sugar levels, potentially triggering cortisol release. Cortisol is the stress hormone, and chronically high levels are typically associated with fatigue and irritability. Therefore, opting for nutrient-dense, whole foods with a lower glycaemic index can help to regulate blood sugar levels and support cortisol and insulin regulation.