Changes in how we talk about mental health has changed dramatically over recent years with celebrities speaking out about their personal struggles with depression and anxiety.  While there can be a multitude of reasons behind these issues the links are growing stronger between what happens with our mood and what happens in our gut.

Alterations in the Gut

Candida Albicans

We literally have trillions of bacteria in our digestive system.  They help us digest food, modulate the immune system and balance inflammatory processes in the body.  While diet is a one of the best ways to

support these bacteria, other things may be out of our control. Top of the list being the use of antibiotics with the more courses of antibiotics taken the greater the risk of depression.

Depressed poo?

One way researcher discovered that alterations in the gut bacteria can influence mood is by transferring a stool sample from a depressed human into a healthy mouse.  What they found was that the mouse started to show signs of anxiety and depression.  Just to make sure it wasn’t the actual transplant procedure which was influenced the change in behaviour they also transplanted stool from a non-depressed human in to a healthy mouse which didn’t change the mouse behaviour at all which indicated a clear cause and effect of the ‘depressed stool’.



Commonly, when we think of inflammation a big red pulsating elbow joint might spring to mind however, inflammation can exist on a much lower level.  Low grade inflammation in the gut is partly regulated but the types of bacteria that live there.  The proteobacteria family of bacteria contain an inflammatory compound in their cell wall called LPS.  The number of these bacteria found in the human gut can range widely from individual to individual from 0.1% to 25%.

The LPS molecule is seen as an endotoxin and has been linked to cardiovascular disease, anxiety, depression and type 2 diabetes.  This is seen to come about by damaging the gut lining which leads to inflammation.  This inflammation then leads to more damage in the gut.  This vicious cycle then allows more of the LPS endotoxin to enter into the blood stream and contribute to low grade and systemic inflammation.

Mice line-up


Perhaps we know serotonin by its other name, “the happy hormone” as its role in mood regulation is so well understood.  This hormone is made from an amino acid called tryptophan which is found in a range of food including salmon, turkey, eggs and spinach.

When we eat tryptophan rich foods it can go one of two ways.  The first is to make serotonin and the other route is called the kynurenine pathway.  Here the tryptophan gets diverted away from making serotonin.  A deciding factor in which route the tryptophan goes down is inflammation.  So the presence of inflammation may result in less serotonin being manufactured and mood may then be impacted.

On observation in studies of depressed individuals was an altered ratio of tryptophan to kynurenine.  This was also seen in the mice after the stool was transferred from the depressed individuals.  We can view the gut as either contributing to inflammation or preventing inflammation and this depends greatly not only on if we’ve taken antibiotics or not but on what we’re eating.


The Western Diet

One thing that is common in the western diet is the increase in processed foods.  Some have even gone as far as to suggest that some of the foods we find in the supermarket should stopped being called food but instead be called ‘food like products’.

In the processing of food one thing that that ends up being removed is a large amount of the fibre.  The role of fibre goes far beyond keep our bowels moving regularly and is actually a key factor in nourishing our gut bacteria.

These gut feeding fibres (prebiotics) are the main fuel sources for many types of bacteria in the colon.  As these fibres are removed we also end up with a higher amount of processed fats which play a role in increasing the LPS absorption into circulation, increasing inflammatory processes and altering the pH in the colon to a more neutral / alkaline level which is more favourable to proteobacteria..  It’s a double whammy of less of the good stuff and more of the bad stuff.


When we feed our bacteria with these fibres they produce compounds called short chain fatty acids (SCFAs) the main one of which is called butyric acid. Throughout evolution the cells lining the large intestine have come to rely heavily on this as their main fuel source.  The gut cells get to eat their fill first and if there’s any left over this can then enter the general circulation where it has further benefits.  These include:

  • Enhanced insulin sensitivity
  • Energy production
  • Protects brain cells
  • Systemic anti-inflammatory effect

For these systemic effects to take place our gut bacteria need to be producing more than the colon cells require.  So how do we best nourish them?



Polyphenols are the colourful compounds found in foods (think red rice, aubergines, black beans, strawberries etc) This can be seen as another category of food compounds that’s lacking in the western diet and that we traditionally ate more of.  In fact, these are mostly unabsorbable to us but they feed and nourish the anti-inflammatory species in the gut helpful to keep the gut balanced.


Resistant Starch and Prebiotics

Similarly, to the polyphenols, resistant starch and prebiotics travel undigested to the large intestine where they feed the bacteria responsible for producing butyrate.  These can be found in a range of plant foods the highest amount of which is in:

Resistant Starches

  • Cooked and cooled root vegetables/rice/pasta
  • Green banana
  • Potato starch
  • Legumes


  • Onion
  • Garlic
  • Leeks
  • Red kidney beans
  • Jerusalem artichokes

The Take Home

While we’re often aware of how we’re feeding ourselves paying close attention to how we’re feeding out gut bacteria can contribute to our overall health.  It’s by keeping the microbes in our guts well-nourished we can reap the rewards of a strengtheed the gut wall, increasing the production of the anti-inflammatory butyric acid and reducing the levels of the pro-inflammatory proteobacteria that we can start to support mood related issues.