The Mind-Gut Connection: Examining the influence of our gut on our mood


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This is a review of The Mind-Gut Connection: How the Astonishing Dialogue Taking Place in Our Bodies Impacts Health, Weight, and Mood by Emeran Mayer, M.D.

You can purchase this book from Amazon.

Published in 2016, The Mind-Gut Connection is a book exploring scientific research of the impact mood has on digestive health and vice versa. It ties into recent ideas around the gut as a ‘second brain’ and the concept of the gut microbiome which is a hot topic at the moment.

Written in an easy to understand way, the book looks at the way our gut microbiome is a unique collection of organisms influenced by genetics, our mothers diet, whether we are breastfed, our early upbringing and our current diet.

Part 1: Our Body, the Intelligent Supercomputer

This section reviews the way the medical model of the body has shifted from that of a machine such as a car–made up of distinct mechanisms that could be replaced when they went faulty–to that of a supercomputer, in which complex regulatory systems mean everything acts as a part of a whole.

…the old fascination with mechanics and engines has given way to a new fascination with information gathering and processing.

The Mind-Gut Connection, p7

This shift has been caused, in part, by gradually declining health outcomes particularly in regard to obesity, diabetes, cancer, heart disease and so on. Dr Mayer argues that

… we have largely ignored the role of two of the most complex and crucial systems in our bodies when it comes to maintaining our overall health: the gut (the digestive system) and the brain (nervous system.

The Mind-Gut Connection, p9

Mayer goes on to argue that the microbiome is capable of influencing our moods, social interactions and even ability to make decisions, thanks to the way the gut influences hormones in our body.

We have all heard of headline-generating experiments in ‘faecal transplants’, which have had all kinds of astonishing results attributed to them. Putting the microbiota from an “extrovert” mouse into a “timid” mouse can cause huge behaviour changes.

The Mind-Gut Connection Runs Both Ways

This communication runs both ways, however. In addition to our gut influencing our mind, our mind also influences our gut. Stress, anxiety, depression–and happiness, peace, tranquillity–all get mirrored within our digestive system.

We’ve all felt the impact being nervous has on our digestion. Get into an argument over dinner and the dinner is ruined and your gut will be churning many hours later.

What many of us may not realise however, is the gut learns from this. Return to the restaurant where you had that argument, and your gut may start churning just in anticipation.

The role of serotonin

The gut stores 95% of the serotonin in your body. Eat a diet low in the amino-acid tryptophan and your brain levels of serotonin will drop. This, in turn, increases the likelihood of depression.

Serotonin influences appetite, pain sensitivity and mood. There’s a reason eating an enjoyable meal leads to a feeling of contentment and well-being!

It’s not just serotonin. There’s a constant flow of hormones, gut peptides, nerve impulses and chemical signals travelling between the gut and the brain. It’s deeply complex and currently poorly understood, but its clear that diet matters.

High fat, low fibre diets

The impact of a diet low in plant-based fibre and high in animal fats–aka the modern or Western diet–has a number of negative effects. High-fat diets lead to an abundance of ‘gram-negative’ bacteria, which reduces the thickness of the mucus lining our gut and thereby makes it more ‘leaky’.

A thin mucus layer means that our intestinal microbes get closer to our gut walls, and the closer they are, the easier it becomes for these microbes to activate the immune system. This causes an inflammatory effect that can spread throughout the body.

Low level chronic inflammation leads to a number of negative side effects:

  • Reduced energy
  • Fatigue
  • Depression
  • Higher pain sensitivity
  • … and may lead to neurodegenerative disorders such as Alzheimer’s

Discover the foods that are high in soluble fibre.

Part 2: Intuition and Gut Feelings

In Part 2, Dr Mayer discusses the impact of early life experiences on the gut. There has been plenty of evidence that adverse childhood experiences is linked with worse health outcomes. Some of these are psychological, but these experiences have also been linked with gastrointestinal disorders.

A number of animal studies have showed the link goes even further. A stressed out mother rat produces timid, submissive rat children. A nurturing mother rat produces sociable and daring rat children. Upon investigation, it was discovered that when rats who had been licked and cuddled as pups were better able to regulate their stress response when placed in stressful situations as adults.

More than that, the stressed, neglected rats exhibited many IBS (irritable-bowel syndrome) like symptoms.

The good news?

As human beings, we have the ability to partially reverse the programming from our childhood.

For example, several mind-based therapies, including cognitive behavioural therapy, hypnosis, and meditation, have all been shown to change the way we appraise situations and body sensations.

The Mind-Gut Connection, p. 123

Dr Mayer goes on to observe that our gut microbiome is formed in the early years of our life, starting with the ones we get from a vaginal delivery and moving on to breast-milk, cuddles and touching. If a mother is stressed–if she perceives the world as dangerous–the baby is programmed to be more careful and less aggressive and outgoing.

Dr Mayer is careful to point out that we don’t know exactly how the ways in which we’ve changed ourselves by the way we’ve changed everything from the way women give birth to the way we eat. Getting stuck in commuter traffic is a far cry from running from lions–but stress is stress.

RELATED POST:  What is fibre?

The good news, according to Dr Mayer, is that with therapies that target both stress (such as antidepressants) and the gut (such as probiotics) it is possible to break the self-reinforcing loop of stress and gut issues.

Can probiotics ease symptoms of anxiety and depression?

Dr Mayer points to preliminary studies, mostly performed on rats, that show that when given a probiotic, the rats exhibited more moderate stress responses to stressful situations or reduced symptoms of depression.

Other studies show a relationship between consuming probiotics and improved mood. However, for the most part, these studies are small. Dr Mayer states that we need more and bigger clinical trials to truly understand the potential of probiotics in the treatment of mood disorders. However, there is no doubt that what we eat can influence the way we feel, so it’s a good idea for all of us to pay attention to our diet.

Can positive feelings contribute to better gut health?

Here, Dr Mayer gets into some speculative science. When we feel good–when our brains produce serotonin, dopamine and endorphins–do these get released into our guts? Mayer thinks yes, pointing to how these chemical ‘switches’ cause gut reactions such as contractions, secretions and blood flow.

Dr Mayer doesn’t get too into the consequences of this, but it suggests that if we want to improve our digestion we may be advised to find ways of improving our mood when eating. Eating socially and slowly, in a relaxed fashion in a nice location may mean better gut health than eating ‘on-the-go’, or at our work desk while answering emails from the boss and thinking about deadlines, even if the lunch in question is the exact same food in both scenarios.

In short–have lunch with your friends and loved ones, not your smartphone.

Part 3: How to Optimize Brain-Gut Health

In this section of The Mind-Gut Connection, Dr Mayer spends some time discussing traditional diets of rural and tribal people who maintain traditional diets. These diets are often very different (from people living in environments as diverse as tropical rainforests vs savannah, but appear to lead to a similar gut microbiome.

Dr Mayer suggests that this microbiome results from a diet that focusses on a large variety of plant-based foods with occasional lean meat. In contrast, in countries with a western diet, or tribes that focus on high-meat diets (such as during the dry season for the Hazda tribe) have less diverse microbiomes with different ratios of microbes.

Sadly, we cannot simply adopt a plant-based diet and except to regain microbe diversity. Our gut microbiome is laid down in the first three years of life, based on our food supply and environment when we are infants.

Not unsurprisingly, Dr Mayer highlights the benefits of breastfeeding over formula, and cites the tradition of continuing to feed babies for extended periods of time.

However, all is not lost. It is possible to make beneficial changes to your gut ‘metabolites’, as our gut microbiome does shift to adapt to what we are eating. It’s one of the reasons humans can radically change what they eat (think ‘fad’ diets, such as going vegan for 30 days, or trying Atkins to lose weight for a wedding) without dramatic consequences. Our bodies are built to respond quickly to different foods and derive nutrition from them.

In short, diet changed the study subjects’ production of microbial metabolites without significantly changing the composition of the microorganisms that produced these metabolites.

The Mind-Gut Connection, p.216

What this means if that, if you are born into a particular civilisation, such as a Western civilisation, you acquire a Western microbiome. However, the microbial metabolites you produce will change depending on the kind of diet you consume.

(Dr Mayer explains this by comparing the microbiome to the musicians that make up an orchestra, and the metabolites to the music. You can’t change the individual musicians, but you can give them a different tune to play!)

A Diet High in Animal Fat Can Harm Your Brain

The Mind-Gut Connection is extremely clear about the dangers of consuming a diet high in animal fats. It switches your immune system into a low-grade inflammation mode that profoundly influences our overall health.

According to Dr Mayer, a high-fat, high-sugar diet can:

  • numb your satiety response causing you to overeat.
  • provoke ‘addictive’ eating behaviours, such as food cravings
  • potentially lead to Parkinson’s disease (there are many unknowns about Parkinson’s disease)

What is the best diet to eat for gut and brain health?

The quick answer?

The Mediterranean Diet.

With a wide variety of plant-based foods, whole-grains and olive oil instead of animal fats, Dr Mayer points to the Mediterranean Diet being the most effective template for healthy eating.

He notes that how we eat can be as important–with a focus on sit-down, sociable, leisurely meals being a key component. We should avoid eating when we are stressed, sad, angry, or afraid.

The Mediterranean daily template includes:

  • At least 5 servings of vegetables
  • 1-2 servings of legumes and beans
  • 3 servings of fruit
  • 3-5 servings of grains
  • 5 servings of plant fats (olive oil, avocado, nuts and seeds)
  • Plus consumption of seafood 2-4 times a week and red meat no more than once a week

There is extensive research into the benefits of the Mediterranean diet. It’s anti-inflammatory, full of fibre, and an excellent choice for almost everybody.

In addition, regular consumption of probiotics, such as from yoghurt, kimchi and sauerkraut can also benefit gut health.

Read The Mind-Gut Connection

Overall, this was a fascinating book. There was somewhat unfortunate language when describing Autism, which pathologised it quite a bit. However, if you are interested in the science I would highly recommend checking it out.

You can purchase The Mind-Gut Connection from Amazon.

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