s a mental health therapist, I have always been interested in the latest research and treatment modalities for people who struggle with mental health disorders. Over half of the clients I counsel struggle with symptoms of anxiety and depression, so when I started hearing about how the bacteria in our gut can have an impact on mood and the stress response, I decided to delve into the research to see what I could find. I sought out the expertise of Dr. Christine Hough, senior researcher in the department of pathology and molecular medicine, to assist me in this endeavor. Dr. Hough also happens to be my mom, someone who has been telling me for over a year to feed my microbiome while dropping off bottles of homemade probiotic elderflower soda at my apartment door. As I drink my daily dose of elderflower soda I wonder if this will really make a difference to mood and stress levels. How on earth could the bacteria in my digestive system exert any influence over my brain? I’ve been aware for quite some time of the ways in which our feelings can impact our gut – I speak with clients regularly who talk about their experiences of having “butterflies” before writing an exam or giving a presentation at work. There has also been quite a bit of research suggesting that individuals who experience early life stresses are at a higher risk of developing gut-related problems, such as irritable bowel syndrome. Well as it turns out, the link between the brain and the gut is a two-way street. There has been an avalanche of research examining the connection between the bacteria in our gut and wellbeing in recent years.

Before I share with you the ways in which our gut microbes can influence our feelings as well as ways in which we can use these microbes to improve mental health, let’s explore what the word “microbiome” really means.

The microbiome is the genetic material of all the microbes – bacteria, fungi, protozoa and viruses – that live on and inside the human body. The greatest concentration of microbial life is in our gut. The bacteria in the microbiome help digest our food, regulate our immune system, protect against other bacteria that cause disease, and produce vitamins. We have far more microbial cells than we do human cells, in fact, the number of genes in all the microbes in one person’s microbiome is 200 times the number of genes in the human genome.

Most of the research that has examined the link between the microbiome and the brain has been conducted on animals. One of the key initial studies that explored this link took place in Japan in 2004. The researchers of this study showed that mice produced and raised without gut bacteria (“germ-free mice”) appear unusually sensitive to stress. When they placed the germ-free mice and normal mice in restraints, they discovered that the mice that lacked gut microbes pumped out roughly twice the amount of stress hormones than the normal mice. Furthermore, when they colonized the germ-free mice with a probiotic species early in life, they were able to correct the stress reactivity response. These findings prompted other researchers to continue investigating how gut bacteria can influence stress.

In 2011, researchers at University College Cork and McMaster University published one of the most prominent studies linking gut bacteria to the brain. They dropped mice into tall columns of water in what they called a “forced-swim test”. When the mice realize that they can neither touch bottom nor climb out of the cylinder, they collapse into a forlorn float, exhibiting “behavioural despair”. Some of these mice were fed a broth infused with Lactobacillus rhamnosus, a bacterium that is used to ferment milk into yogurt and also found in humans. This type of bacteria releases a neurotransmitter called GABA, which helps to calm the nervous system. The researchers found that the mice that were fed the bacteria-laden broth kept swimming longer when dropped in the cylinder and spent less time in the forlorn float, behaving as if they were in a more relaxed state.

In 2016, researchers Dr. John Cryan and Dr. Ted Dinan transplanted the microbiome of depressed patients into animals. Rats that received the depressed microbiome exhibited many of the same behaviours as the depressed individuals. For example, one of the key features in depressed people is that they lose interest in the things that they normally would find enjoyable. When the rats were given the bacteria from the depressed individuals they no longer cared to enjoy a treat of sugar.

Many of these animal studies have led researchers to hypothesize that by modifying the microbiome of humans through the use of supplements containing probiotics, perhaps we can improve symptoms of depression and anxiety. In 2015, researchers from the Netherlands conducted a randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to low mood. Compared to participants who received the placebo intervention, participants who received the 4-week multispecies probiotics intervention showed reduced cognitive reactivity, specifically, rumination and aggressive thoughts.

Now, before you start popping probiotics to improve your mood, keep in mind that probiotic supplementation requires a great deal more research as a potential preventive strategy for depression. That being said, some research has proven that the food that we eat can make a big difference to our mood. Dr. Cryan and Dr. Dinan have some practical tips based on their research:

Get some fiber

The by-products of fiber digestion have been shown to increase levels of serotonin, a hormone associated with positive mood regulation. Try roasting veggies with some fruit and nuts, here are some ideas:

• Brussels sprouts, grapes and walnuts
• Cauliflower, chopped apricots and pistachios
• Cabbage wedges, cherry tomatoes and hazelnuts

Delicious!

Try fermented foods

Fermented foods are rich in probiotics. Sauerkraut, kimchi, kefir, kombucha and real natural yoghurt, all stimulate the growth of beneficial bacteria.

Start cutting out junk food

Highly processed foods might actually induce depression, possibly by boosting pathogenic bacteria. For instance, emulsifiers used in ice-cream and bought cakes have been shown to thin out our body’s protective layer of mucus which prevents pathogenic bacteria embedding themselves in the gut lining and thus protecting us from inflammatory diseases linked with depression.