Could our gut health be influencing our mental health?

The incidence of IBS is rising dramatically worldwide. This is also the case for mood related conditions such as anxiety and depression. As many of you will already know, gastrointestinal problems, such as irritable bowel syndrome (IBS), are commonly linked to anxiety & mood changes.

In the body, single cell organisms– primarily in the form of bacteria– outnumber human cells ten to one. Over 100 trillion of these microbes reside in the gastrointestinal tract, where they are hard at work breaking down food to extract useful vitamins and minerals, and taking action against harmful pathogenic invaders when needed.

In addition to their roles in optimising the digestive and immune systems, these bacteria in the gut also partner with the nervous system to send messages throughout the body and to the brain.

The digestive tract has deep, physiological connections to the central nervous system. We already know that information relating to hunger and satiety must be exchanged between the two in order for us to survive.

The gut even has its very own set of nerve cells, embedded in the intestinal walls. These millions of GI neurons make up a highly integrated network called the enteric nervous system (ENS). With as many neurons as the spinal cord, the enteric nervous system is so complex that some have called it the “second brain.”

The vagus nerve, nicknamed the “wandering nerve” serves as the major channel between the enteric and central nervous systems. It is the longest cranial nerve and it extends from the brain stem right down to the abdomen, allowing signals to pass between these locations.

Interestingly, about 90% of the fibres in this nerve carry signals upwards from the bowels toward the head, and not the other way around. This alignment allows the microbes in the gut to send powerful messages that can actually influence our emotional processing that occurs in our brain.

Some thoughts influence the digestive processes in the gut such as thinking about eating a delicious meal can make your tummy grumble. But the gastrointestinal tract is also sensitive to emotions, and feelings can even trigger symptoms in the gut. Such as being nervous, which can cause people to have ‘butterflies’ in their stomachs. In fact, the communication runs both ways – the gut also communicates with the brain and can influence our emotions.

The impact of pathogenic bacteria

Gastrointestinal infections have a hugely negative impact on the lives of millions of people worldwide. This can include an infection with a parasite, pathogenic bacteria or yeasts in the large intestine and also a bacterial overgrowth in the small intestine (SIBO). While an acute infection may get picked up, many of these infections go undetected and get labelled as IBS. Many IBS sufferers also experience mood related symptoms such as depression or anxiety. People are told that there is no cause or cure for their IBS. When in reality, if an underlying infestation is dealt with, the individuals IBS will also clear up, and often in my experience so will the anxiety/ depression.

These infections and the associated inflammation that comes from dysbiosis in the gut microbiome can change the normal chemical pathways in our brains. Our brain chemistry changes in response to inflammation and lipopolysaccharides (LPS) activity. LPS are toxins which are produced by harmful bacteria in the gut. This can result in serotonin and melatonin not being made in the volume we need. We need these chemicals to regulate our mood, sleep and gut motility/health. When our brain chemistry is out of balance, we can feel depressed and anxious, have a harder time sleeping and feel less motivated. This cycle can increase cortisol, a stress hormone, turning our bodies on high alert, which can worsen depression and anxiety.

Roles of Probiotic Bacteria

The idea that the microorganisms in our gut could influence how we think and what we feel is profound. To understand this gut-brain connection further, here are some of the main pathways through which bacteria in the gut impact the nervous system:

• They promote growth and development of neurons. Compounds produced by the microorganisms in the gut stimulate the release of neural growth factors, the proteins that encourage the formation and survival of nervous system cells. Research is now suggesting that even before birth, maternal-fetal transmission of bacteria occurs through the amniotic fluid and umbilical cord blood, stimulating early nervous tissue development. After birth, microbes from the outside environment (including those from breastmilk, foods, contact with siblings and pets, etc.) continue to enter the body and shape the nervous system throughout late childhood and beyond.
• They stimulate memory and learning. Certain strains of gut bacteria produce chemicals that stimulate a sympathetic, or “active” response in specific parts of the brain. Often this occurs in regions involved in decision-making, planning, and attention such as the frontal cortex and hippocampus. Bacterial metabolites are therefore very important for jump starting the biochemical processes involved in memory and learning.
• They guide changes in mood. Select microorganisms help to produce mood-regulating neurotransmitters like serotonin, GABA and melatonin. Over 30 different bacterially-derived neurotransmitters work locally in the tissues of the gastrointestinal tract, and also relay signals to the central nervous system. It has been suggested that almost 95% of the body’s serotonin is produced in the gut. Serotonin (our happy, feel good neurotransmitter) has many functions in the brain including regulating our mood, anxiety, mental focus, clarity of thought etc. However, it also has many function in the gut too including satiety (feeling full), digestion, nutrient absorption, peristalsis.
• They shift digestive patterns. Metabolites from bacteria stimulate sensory nerves in the intestines to change gut motility patterns. Feedback from these motor changes is then relayed to the brain, where a response is elicited. Pain and anxiety are two of the most common reactions. This cross-talk is one of the reasons why psychiatric disorders are often accompanied by chronic digestive problems and vice versa.
• They can innfluence the expression of genes. It was once believed that genes were destiny. However, it is now known that many lifestyle factors have a profound influence on the ways in which genes are expressed. The study of epigenetics has revealed that microorganisms play a large part in this. Bacteria in the gut hold the potential to change patterns of DNA methylation, thus switching certain genes on or off.

Could probiotics be used to treat conditions such as anxiety and depression?

The short answer is yes, although much more research will be needed before targeted clinical approaches are applied mainstream.

In the meantime, there are many steps that you can take to strengthen the gut microbiome and heal from mood related disorders.

• A nutrient-dense diet filled with fermented foods is a powerful place to start.
• Supplementing daily with a probiotic is another crucial step. This is even more important for anybody who has ever had to take antibiotics in their life. Even one round of antibiotics in childhood can negatively affect your gut microbiome as an adult.
• Dealing with any underlying pathogenic gut infestations.
• Healing from intestinal permeability AKA leaky gut.  
• Opting for gentle personal care products that won’t destroy beneficial bacteria is another often-overlooked step, as is drinking pure, filtered water and eating an organic diet.
• It is really important to get your vitamin D levels checked as this can often contribute to low mood and a weak immune system. A damaged gut can affect the absorption of vitamins and minerals essential to provide the raw material for our neurotransmitters and hormones.

For those seeking more specific and personalised treatments, working with a functional medicine practitioner or nutritional therapist who can help develop an individualised plan would be hugely beneficial.

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