How Food Affects Mood

 The connection between mental health and diet has been a hot topic of discussion in recent years. We now know there are strong links between the gut microbiome and the brain. But how do signals get from the belly to the brain and what effect do they have when they get there?

We know that signals from the gut can reach many parts of the brain including the insula, limbic system, prefrontal cortex, amygdala, hippocampus and the anterior cingulate cortex which translate very roughly to areas of the brain related to self-awareness, emotion, morality, fear, memory and motivation. The signals between the brain and the gut are transmitted through the vagus nerve. The vagus nerve is the fastest route from the gut to the brain and runs up through the diaphragm, between the lungs and heart, up to the oesophagus through the neck and then to the brain. Studies have shown that stimulation of the vagus nerve significantly improvement quality of life in people with depressive disorders [30152645].

With a huge surface area and a massive system of nerves, the gut is considered one of the body's largest sensory organs. The connection between the gut and the brain was first studied in humans two years after experimenting on mice. In this study, certain areas of the brain responsible for processing emotions and pain were found to have been unmistakably altered following four weeks of oral administration of select bacteria [21683077] [21876150].

Irritable bowel syndrome (IBS) is characterised by bloating and uncomfortable bowl movements with either constipation, diarrhoea or both, and a general feeling of unease. Sufferers also have an above-average incidence of anxiety and depressive disorders.

Despite ample evidence that this syndrome is strongly influenced by persistent inflammation, undetected food intolerances, and 'bad gut flora', many medical practitioners still dismiss patients concerns as 'psychosomatic'. Equally, patients with Crohn's disease, ulcerative colitis, and chronic bowel inflammatory diseases have a much higher rate of depression and anxiety.

The good news is that diet plays a huge role and can often reverse or even cure these diseases, without the need for radical medical intervention such as surgery. 

With depression and anxiety ranking among leading causes of disability around the globe, it is important to question the role nutrition has to play. Today, backed by the expanding research done in the field of nutritional psychiatry, the focus has partly shifted to helping people understand how what they eat, along with the types of bacteria that inhabit their gut, can positively or negatively affect their mood.

Gut bacteria produce around 90% of the neurotransmitter serotonin in your body [30138667]. Since serotonin influences mood, sleep, appetite, and pain inhibition, it makes sense how your gut and the foods you put into it may influence your mental state. These good bacteria offer a host of health benefits too such as decreased inflammation, and protection from toxins, to name a few. So, it's important to feed them the right foods so they can do their job properly.

Several studies have shown that reducing intake of unhealthy foods and increasing nutrient intake may help to reduce symptoms of depression [30720698]. Participants were advised to increase fruits, vegetables and fibre consumption, including whole grain breads, fish twice a week, and nuts and seeds in their diet, while also reducing their intake of refined foods, and or meat/animal fats. The ways in which these dietary changes are thought to influence mental health are related to the wide array of compounds found in these healthy foods. These compounds positively interact with pathways of oxidative stress, inflammation, stress response, immune function and brain function, all areas which are shown to be disrupted in people with mental disorders and/or an imbalance of gut bacteria. For example, fruits and vegetables contain polyphenols which are known for their anti-inflammatory, anti-oxidant and brain protective effects. The abundance of fibre, vitamins, minerals, omega-3 fats, and probiotics often found in these diets also modulate these pathways and may offer protective benefits for mental health.

Recent research also suggests that better quality diets, such as the Mediterranean diet, and avoidance of pro-inflammatory foods such as processed meats, sugar, processed foods, saturated fats, and trans-fats are associated with lower risk of depression, while unhealthy diets, typically higher in these foods, are associated with increased anxiety. Pro-inflammatory foods such as these are thought to alter the gut microbiome, tipping the balance in favour of the bad gut bacteria which may activate these inflammatory pathways and affect mental health [30254236] [24489946].

Traditional diets, like the Mediterranean diet, tend to be high in vegetables, fruits, nuts, unprocessed grains, legumes, fish, and seafood. They are also low in or completely void of red meat, and processed, refined foods that are high in salt, sugar and saturated or trans-fats.

There's still plenty more research needing to be done but it's worth trying some of these changes in your own diet to see how eating different foods makes you feel.

As Michael Pollan famously said:

Eat food, not too much, mostly plants.


Written by
Alannah Mezzatesta, BSc
Nutrition Scientist (ANutr)
last updated  27th July 2022