Modify your Microbiota & Improve your Mood

The gut-brain axis is an incredible bi-directional communication network - like a super highway between gut and brain - that connects our gut bacteria, stress response, our hormones and immune system, and our life experiences to date - integrating them all to influence our physical well-being, and mental health. This excellent article in our library is a great overview of the gut-brain connection - start here if you’re new to anything gut-brain!

Let’s go deeper into the role of gut bacteria - our “microbiota” - on symptoms like depression and anxiety.

The microbiota is the collection of microorganisms living in our digestive tract, including bacteria, fungi and viruses. It’s like a hidden garden that we tend to that can either result in a flourishing, diverse and healthy ecosystem (think rainforest) or otherwise might be closer to a pine plantation or even weedy toxic overgrowth. Most importantly, it's modifiable (for better or for worse!) with every bite we choose to eat - we have the capacity to change it.

We’ll look at:

• Can these microorganisms influence emotional behaviour and function, even in the absence of any obvious “gut issues”?

• Could they contribute to anxiety and depression symptoms?

• How do they cause anxiety or depression symptoms?

Does the microbiota influence mood?

A number of key studies over the last decade have suggested that the composition of the gut microbiota, and medicines that affect it, have the potential to change emotional behaviour and brain function.

A systematic review looking at antibiotic use - medicines that induce substantial changes in the gut microbiota - and the risk of depression, found a potential association. Antibiotic exposure was associated with the subsequent development of depression, with some larger studies of over 1 million participants indicating the increased risk may be as high as 20%. The risk was higher with the more courses and types of antibiotics used, and persisted for 10 years. Similarly in babies, antibiotic use within the first year of life was associated with a greater risk of behavioural difficulties and depression by the age of 3.

In 2016, a fascinating study titled “Transferring the blues” took faecal material from depressed people and transferred it to rats who had been raised without gut bacteria of their own. The rats began behaving in ways consistent with depression and anxiety, such as a loss of interest and pleasure in their normal activities, and increased anxiety behaviours. Neurotransmitters in the rats brain’s were altered and they had body-wide inflammation. The control group - rats transferred faecal material from healthy people who weren’t depressed - continued to behave normally. The research team concluded that gut microbiota may play a causal role in the development of depression, and might provide a new target for both the prevention and treatment of depression and anxiety.

3 key ways microbiota may influence mood

Since then, researchers have started to delve into how the microbiota might be influencing our mood. Let's look at three main ways.

1. Endotoxins shed from gut bacteria

Endotoxin is a structural part of the outer membrane of certain bacteria - and it's strongly inflammatory. It's been linked to a range of Western diseases such as Alzheimer's, cardiovascular disease, Type 2 diabetes, and depression and anxiety.

When bacteria containing endotoxin are broken down as part of their normal life cycle, this endotoxin is shed into our intestines, where it can:

• damage the intestinal barrier (causing “leaky gut”);

• cross the blood-brain-barrier to inflame the brain (cue depression and anxiety);

• lead to body-wide inflammation.

Everyone has some level of endotoxin shed into the gut by bacteria - but the key is that the overall proportion of bacteria shedding harmful endotoxin varies widely.

Proteobacteria for instance, a group of bacteria that have particularly harmful endotoxin, may make up only 0.1-0.5% of a person’s ecosystem, similar to the level of hunter-gatherer societies, but could go as high as 25-30% of the ecosystem in cases of serious dysbiosis (disruption to a person's microbiota). The latter person would have 30x the level of endotoxin to process!

The more endotoxin you have, the greater the level absorbed into the gut that may go on to inflame the body and brain.

2. Endotoxins likely alter neurotransmitter pathways

When we eat the amino acid tryptophan from foods such as chicken, cheese and fish, it’s processed in two main ways. One pathway leads to serotonin, the helpful brain neurotransmitter - the other pathway leads to kynurenine, where the accumulation of compounds harmful to the brain can result.

The level of inflammation in our body determines which pathway the tryptophan is sent down. More inflammation means more tryptophan down the kynurenine pathway, eventually leading to altered ratios of serotonin to kynurenine. Altered ratios have been observed in depressed people, and also in the depressed rats who received stool from depressed humans, suggesting that inflammatory endotoxin from gut bacteria can influence these pathways.

The Kynurenine Pathway

3. Butyrate - produced by bacteria - helps mood

Bacteria in our colons produce either one or a combination of three short-chain fatty acids - acetate, propionate and butyrate.

Our colon cells have evolved to rely on microbiota-created butyrate to survive and be healthy. It's the main food source for our colon cells. We also know that it protects the small intestine (as well as the colon) and has a whole heap of body-wide benefits - such as enhanced insulin sensitivity, upregulated mitochondria function, protection against brain inflammation caused by endotoxins, and full-body anti-inflammatory effects.

Crucially, to get the benefits of butyrate, we need to be producing more than our colon cells require.  We want to be nourishing the particular bacteria that produce butyrate to make plenty of it for us, so we can experience its anti-inflammatory benefits.

To sum up

Our microbiota - the actual ratios of microbes there - can either contribute to a diverse and flourishing inner ecosystem that prevents inflammation and improves our mood, with the production of anti-inflammatory substances like butyrate;

OR

can contribute to inflammation in the body and brain via the release of inflammatory endotoxins and an increase in the kynurenine pathway, seen in both depressed animals and humans.

Stay tuned for part 2, where we delve into modifying the microbiota. We'll go over simple but specific dietary and lifestyle interventions that nourish and feed our beneficial microbiota, encouraging a diverse and flourishing inner ecosystem that supports our body and brain to thrive.