The trusty old gut-brain axis is responsible for far more than you might imagine. Take sleep, for example. Writer Alex Sims explores the two-way relationship between digestion and rest.
Often called the body’s “second brain”, the true extent of just how much our gut impacts the way we live is becoming more and more understood. After decades of scant research, scientists are beginning to discover just how huge a role our gut plays in our health, affecting everything from our moods and emotions to our immunity.
Now another pivotal factor in our lives is also thought to have a closer relationship to our gut than we could ever have imagined: sleep. Research in this area is extremely new, but experts agree there is a deep symbiotic relationship between sleep and gut health.
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“Sleep and gut health are linked to each other in multiple ways,” Naomi Leppitt, gut health specialist dietitian for Dietitian Fit & Co, tells Stylist. “Studies show that the types of bacteria in your gut and the richness of bacteria can promote good sleep – from how long you spend in bed to how quickly you fall asleep and whether you’re more likely to wake up in the night or not.”
At the heart of all this is the gut microbiome (GM), a unique ecosystem of trillions of tiny organisms and bacteria living in our digestive system. Everyone has their own unique GM. Created in the first 1,000 days of life, it quickly develops into a sophisticated neural network that transmits messages from our brain to this human gut ecosystem – a communication system known as the gut-brain-axis.
“The microbiome is now known to act as an endocrine organ, producing hormones that influence mood, energy metabolism and insulin resistance and may have a significant impact on glucose control, cholesterol levels, obesity, sleep, energy levels and fatigue in ways that are not yet fully understood,” explains Dr Sarah Brewer, medical director at Healthspan and registered nutritionist.
This means what’s inside our gut can impact our sleep in a host of different ways, one of which is the hormones it helps to release into the body.
Serotonin is made in the gut and affects our sleep quality
When we have a healthy balance of digestive bacteria it stimulates the production of serotonin in the interstitial wall. “In the gut, serotonin regulates bowel movement and how the brain responds to signals relating to bowel contraction,” explains Dr Brewer. “Within the brain, serotonin helps to lift mood and improve anxiety and depression.”
This serotonin is also converted into melatonin in the brain – our natural sleep-inducing hormone explains Dr Brewer. Studies have also shown that an imbalance of bacteria in the gut – a condition known as dysbiosis – may be connected to fragmented sleep and short sleep duration.
The gut is linked to our circadian rhythm
It’s also thought our gut is closely connected to our circadian rhythm, our body’s 24-hour internal clock, which helps it carry out essential functions and processes. One of the most well-known circadian rhythms is the sleep-wake cycle. Experts suggest that if our melatonin levels are altered it can change our integral sleep-wake cycle.
“Melatonin is produced not only in the brain but also in the intestine by certain bacteria,” explains Leppitt. “So if you have a healthy gut, it will be producing melatonin and helping to keep your body clock in check.”
Our guts do a ‘housekeeping wave’ when we’re asleep
We also know that only when the body is sleeping can it perform an essential migrating motor complex known as a “housekeeping wave”. “This is like a daily swoosh of all the bacteria from the small intestine to the colon,” explains Sarah Grant, nutritional therapist at Gut Reaction. “It helps regulate our bowel movements, protect against bacterial overgrowth and things becoming stagnant in our guts. In order for the body to do this, it has to be in a restful mode – it’s another example of sleep and gut health supporting each other.”
But, we can’t forget the gut-brain axis is a two-way process. So, in the same way, it’s important to understand how what’s going on in our guts affects our brain and how it goes into sleep mode, it’s also important to understand how what’s going on in our brain affects the gut.
Stress affects both brain and gut
When we’re stressed and anxious it can be difficult to drift off, and this can have an impact on our digestive health. Research has suggested that loss of sleep and raised stress in the body can increase the gut’s permeability, also known as leaky gut, where food or toxins can cross the barrier from the gut into the bloodstream and the rest of the body. “Lack of sleep will trigger the immune system to release more pro-inflammatory cytokines (small proteins essential in cell signalling), which worsen gastrointestinal disorders,” says Leppitt.
“Or, if you’re up at night as you’re anxious, you might find you get more gut symptoms like constipation or diarrhoea because blood flow is redirected away from your gut to your limbs as the fight-or-flight response is triggered.”
So now we know how the brain and gut work together to influence our sleep, how can we make sure we’re safeguarding our gut health so we can drift off more easily?
How to improve gut health for better sleep
Think about fibre
To make sure our brain-gut axis is working as proficiently as possible, it’s important our gut microbiome has a diverse and healthily balanced range of bacteria.
“Diversity in the gut is key,” says Dr Meg Arroll, a chartered psychologist at Healthspan and the author of IBS, Navigating Your Way To Recovery. “The more diverse the microscopic communities that call our guts their home, the better sleep efficiency and duration and less disturbed and fragmented sleep (bearing in mind that it’s completely normal to have periods of wakefulness during the night as we progress through sleep phases).”
Increasing your fibre intake is an easy way to make sure your GM is as diverse as possible. Health nutritionist Charlotte Turner suggests aiming to eat around 30g of fibre a day, particularly non-digestive fibre, such as wholegrains, wheat bran, beans and nuts.
“Simple ways to achieve this include aiming to have a portion of fruit and vegetables at every meal even breakfast or sprinkling seeds or nuts on salads, porridge or your yoghurt to really boost your fibre content,” adds Turner.
“Whole foods, legumes, fruits, vegetables, olive oil and nuts increase levels of good bacteria in the gut, while avoiding foods that are sugary, fatty or highly processed will starve the bad bacteria,” says Leppett.
Eating a diverse range of fibres to encourage a diverse range of good bacteria is even more beneficial. One way to do that is to change up your fruits and veg of choice in your weekly shop and trying out some new ones. Eating different varieties of colourful vegetables is a good way to do this, as is taking a probiotic. However, like snowflakes, all our microbiomes are unique, so make sure you choose the right probiotic for you.
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Keep it regular
Thanks to our circadian rhythms constantly working around in the background, our bodies love routine, and our guts are no different. In fact, we can use our meal times in order to help set our circadian rhythm and keep our sleep-wake cycle in check. “It’s thought that meal times might help feed that cycle, which would regulate sleeping as well,” says Grant. “The gut microbiome is thought to show some rhythmic fluctuations itself that will play into the circadian rhythm.”
It’s also important to leave some time between eating and sleeping so our bodies aren’t busily digesting our food while we’re trying to get some rest. Eating at least two or three hours before bed is a good rule of thumb.
Drink the right liquids
Not all liquids are created equal when it comes to our gut. While water can help soften our stools and make them easier to pass when we go to the toilet, coffee is a different matter. “Caffeine is a gut stimulant, meaning too much caffeine can cause a few unwanted symptoms such as bloating and/or going to the toilet more often,” explains Turner. “Plus having more than two or three strong caffeinated beverages of coffee can stay in your system longer than you think, affecting your sleep cycle.”
Taking care of our mental health and looking after the brain side of our gut-brain axis is also important. “We know that the microbiota gut-brain axis acts in both directions, where gut bacteria influence health including anxiety, depression and cognition; however, psychological states can alter gut health,” says Leppett. “As stress impacts the gut – and the brain – incorporate meditation into your day or as you get into bed. This can have positive impacts on stress levels, sleep quality and the gut.”
Doing something as simple as changing the side you sleep on can help your digestion. “To aid sleep and digestion, it is better to raise the bed or mattress and sleep on your left hand side,” says Leppett. Gentle exercise like yoga or a light walk in the evening can also be beneficial.
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