How our gut can wreck our mood
We’ve always known that our brain and gut communicate. It’s why we feel butterflies in our stomach when we’re nervous or have a “gut feeling” when something isn’t quite right. Both are caused by the brain sending orders to our digestive tract.
Scientists once assumed that these signals were one-way. Research in the last 10 years has shown that not only do signals travel both ways but that the vast majority – about 80% of the communication between the two organs – are in the direction from gut to brain.
They mainly do this through the vagus nerve, which, at half a metre long, is the longest nerve in the body. It traverses all our intestines and weaves its way up through our lungs and heart, past our ears and into our brain. It’s a much more sophisticated communication system than we thought possible. This is how the brain knows what’s going on in our body, how to react and predict what to do next.
What we’ve learnt is that irritation in our digestive system – typically caused by an unhealthy diet – can put our brain on high alert. This happens because our immune system (70% of which coats our gut) produces chemicals that cause inflammation when the gut is disrupted.
The brain detects that this has happened and senses that you’re unwell and more vulnerable to infection. It makes you want to stay in bed, under the duvet and deprioritise pleasure – from food, partying, sex – so that you can recuperate. All because the immune cells in the gut are reacting to what we eat.
When you understand this, it makes sense that changing your diet will alter your gut lining and impact your mood, for better or worse. Studies have found that people who eat healthy diets – full of fruit, vegetables and whole grains – have a better mood.
Conversely, big epidemiological studies show that people who eat the most ultra-processed foods (UPFs) – junk food like crisps, biscuits, fizzy drinks, ham, sausages, chicken nuggets and sugary cereal – have the biggest risk of mental health problems. When people have moderate depression, giving them a gut-friendly diet can improve or reverse symptoms in a significant proportion of them.
Obviously, your mental health isn’t entirely dictated by diet. There are multiple causes: genetics (plays a general role in susceptibility to any disorder), trauma, environmental stress and sleep disorders. But it’s also true that simple lifestyle changes can modify signals to the brain and reduce our risk of poor mental health, whether that’s a bad mood or anxiety and depression. I have now learned to listen to my body, and realise that low mood and fatigue are symptoms of inflammation. Until now, we’ve totally ignored the role that food can play.
For most people, there’s a lot more they can be doing to look after their gut health, and therefore mood. This is what I did.
I swapped pre-made sandwiches for sardines on toast
Through my 30s, 40s and 50s, I ate a low-fat, starchy diet with quite a lot of UPFs and hospital food: cereal or toast with marmalade for breakfast, a tuna sandwich from a vending machine for lunch. There wasn’t a vegetable in sight and the occasional banana was the only fruit I would have.
My blood sugar was constantly spiking and crashing, causing low-level inflammation that was sending confusing signals to my brain that left me feeling pessimistic, moody, exhausted and unproductive by the afternoon. I was a busy doctor and father, so not all of my problems would have vanished by eating better, but it certainly would have helped.
Now, I have brunch instead of breakfast and lunch, often my homemade bread with mushrooms, anchovies or sardines, topped with nuts and seeds. Research shows that regularly eating mushrooms reduces your risk of dementia by around 30%, nuts have been shown to do something similar and oily fish has omega-3s that lower the risk of dementia and boost mood.
Just like we want to supply our heart and muscles with the right nutrition, the brain is the same. The brain is less than 5% of our weight but burns through 25% of our calories. It’s the greediest organ in the body, so what we eat is going to be most salient to our brain.
For my mood and overall brain health, I also aim each week to eat 30 different plants (fruit, vegetables, grains, beans, pulses, nuts, seeds, coffee, herbs, spices). Red, green and yellow peppers count as three different plants. Polyphenols – compounds found in berries which have – are especially helpful for the brain, as are flavanols found in chocolate, so I enjoy eating those and avoid UPFs.
It’s important to occasionally give yourself a treat. My favourite comfort food is pavlova, which my mum used to make me. In my cookbook, I share a recipe for a version that still puts a smile on my face but has much less added sugar.
It’s about making better choices, based on the latest science. If you do that, you’ll be happy for a lot of reasons because you can wean yourself off mood-worsening UPFs, create colourful meals, full of fibre, that you enjoy. You really can control your brain to a certain extent with what you put in your mouth.
I’ve upgraded to seven and a half hours of sleep
My sleep has improved a lot in the last 15 years, since I improved my diet. It no longer takes me two hours to get to sleep. Dinner is at 7.30pm as eating too close to bedtime reduces sleep quality. An earlier dinner also means the gut gets a longer rest overnight, which gives it more time to repair, supporting my mood and brain health.
I try not to work in the evenings, which I always used to do. I’ll have a bath, read my book and have invested in blackout blinds. I usually sleep all the way through to 6.30am. It’s definitely one of the reasons I’m happier.
I prioritise exercise and new hobbies
Mood isn’t all about diet and sleep. Regular exercise has been shown to lower inflammation, so it works in a similar way to swapping from an unhealthy to nutritious diet. I used to hit 20,000 steps when I worked in the NHS from dashing around the hospital but did no other exercise. Now, I’m always mixing things up with Pilates classes, yoga and weights. I keep trying to learn new things too, like kitesurfing or Catalan – so that my brain is forming new connections.
It might be my life stage, but I am more content than I’ve ever been: things feel settled and stable and I have no doubt that prioritising my brain health is playing a part.
