A Nutritional Psychiatrist On How Your Diet Can Influence Your Mood

By Dr Uma Naidoo

Have you ever felt clearer and more mentally sharp after a week of healthy eating? There’s a reason for that—and it all comes down to the gut-brain connection

“Despite being located in completely different parts of our body, our brain and our gut are in constant, bidirectional communication with each other,” explains Dr Uma Naidoo, who is a Harvard-trained nutritional psychiatrist, professional chef, nutritional biologist, and author of This is Your Brain on Food.

Some of the most obvious examples of this include losing your appetite when you’re nervous or that sinking feeling in the pit of your stomach when you realise you’ve locked yourself out of the house. The gut-brain connection means physical feelings in your gut can arise from just a few thoughts.

Of course, as Dr Naidoo shares, there’s a bit more to it than that. “The health of our gut directly influences our mental health,” she says. So how does the gut-brain connection work? What are the tell-tale signs of poor gut health? And how can we eat for better mental health? Dr Naidoo explains… 

How Does The Gut-Brain Connection Work And Why Is It So Important? 

I like to think of the gut-brain connection as a bidirectional superhighway. Signals (in the form of neural impulses) travel back and forth between the gut and the brain via a long nerve called the vagus nerve.

The vagus nerve originates in the brain stem and travels all the way down to the gut, where it forms numerous small branches that wrap around the entire gut. This intricate wrapping around the outside of, and penetrating into, the gut is called the enteric nervous system (ENS). Via this connection, the brain is able to send chemical signals to the gut and directly influence digestion, as well as the composition of our gut microbiome. 

An interesting and particularly important fact about the enteric nervous system is that it houses approximately 90% of the body’s serotonin receptors. Given serotonin [has been] heavily studied in connection to emotion and mood, this finding supports the hypothesis that the foods we eat can dramatically impact how we feel mentally and emotionally.

Where Does Our Diet Come Into The Picture? 

Our guts are inhabited by trillions of different microorganisms, including bacteria, viruses, and fungi, that are collectively referred to as our gut microbiota. The word microbiome refers to the genetic code of these gut microbes. Microorganisms often get a bad rap as being pathogenic, disease-causing agents, but not all of these ‘gut bugs’ are bad. There are actually both helpful and harmful microbial species in our gut, and the helpful species are extremely important to our overall health and wellbeing.

Ideally, the helpful species will outnumber and dominate the harmful species. You can think of them as competing for space and resources, with clear winners and clear losers. The foods we choose to consume on a daily basis dramatically influence the outcome of this ‘microbial war’ by dictating which microbial species will thrive and which will struggle.

The microbes thrive on fibre which we can easily get from a plant-rich diet of vegetables, fruits, whole grains, legumes, nuts, seeds and lentils. By eating these foods, we are fuelling and providing reinforcements to the helpful microbes. These helpful microbes then process the foods we eat and generate their own metabolic byproducts, which confer a number of health benefits to us as their human hosts. These byproducts can be immune-regulating molecules (such as short-chain fatty acids), precursors to important neurotransmitters (such as serotonin or dopamine), or other compounds that influence the ability of our gut to absorb nutrients from the food we eat.

On the other hand, if we choose to follow the standard American diet (SAD), we are creating a hostile environment for the helpful microbes in our gut. The standard American diet consists of foods high in refined carbohydrates and unhealthy fats (such as French fries, potato chips, and pizza) alongside processed red meats. These foods fuel the growth of harmful microbial species, which then begin to take over the gut (a phenomenon known as dysbiosis). Rather than improving our health, the metabolic byproducts produced by harmful microbes damage the lining of our gut and can cause inflammation throughout the body (including in the brain). More and more research is suggesting that inflammation in the brain may play a role in mental illness, so here we see one mechanism by which food may influence our gut health, and, in turn, our mental health. 

What Are The Most Common Signs Of Poor Gut Health?

I am hesitant to say that there are sure-fire, tell-tale signs of poor gut health. There are absolutely certain symptoms and conditions that can be indicative of an unhealthy gut, but these symptoms can also be caused by a number of other factors. For this reason, I always recommend consulting with your physician before deciding that your symptoms are caused by poor gut health. While improving your diet and taking steps to cultivate a healthy gut microbiome certainly won’t hurt you, it’s very important to ensure that your symptoms are not a sign of another, potentially more serious illness. With all that said, here are some common signs and potential indicators of poor gut health:

Mental and emotional symptoms

  • Brain fog
  • Fatigue
  • Anxiety
  • Irritability
  • Low mood
  • Increased distractibility
  • Difficulty with regulating emotions

Physical symptoms

  • Bowel and digestive issues (bloating, constipation, diarrhoea, irritable bowel syndrome, etc.)
  • Acne or other skin conditions (psoriasis, eczema)
  • Difficulty sleeping
  • Difficulty losing weight
  • Joint pain
  • Thyroid conditions (hypothyroidism, hyperthyroidism)
  • The presence of autoimmune diseases (Celiac disease, fibromyalgia, multiple sclerosis, rheumatoid arthritis, etc.)

Note: This is certainly not an exhaustive list, as poor gut health can manifest itself in a number of different ways. Also, I want to reiterate that these symptoms and conditions may have another underlying cause entirely – so speaking to your own doctor is key.

4 Tips For Eating For Better Mental Health

  1. Eat whole, be whole. Choose more healthy whole foods than a processed version. For example: eat an orange but skip the grocery store OJ which has no fibre and a lot of added sugar.

  2. Start small. Consistency and balance are key when it comes to improving your diet and gut health. If you currently only eat vegetables twice per week, I would not ask nor expect you to begin having vegetables at every single meal, seven days a week. In order to be successful, any changes you make must be sustainable for the long term.

  3. Follow the 80/20 rule. As much as you can manage, eat actual food most of the time while being flexible and understanding that life happens you can always course correct at your next brain-healthy meal.  

  4. Spices are part of your brain food pharmacy. A pure spice (not a blend) is calorie-free, salt-free and sugar-free, yet packs a powerful punch of flavour to your food while adding brain-healthy nutrients too. 

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