We asked Dr Sarah Jarvis to dig into the science of stress, how it can impact your gut and tips on how to fight it. Grab a cuppa because this is a deep dive.
What is stress?
The World Health Organization defines stress as ‘a state of worry or mental tension caused by a difficult situation’. It’s important to remember that stress is a normal reaction – we all feel a bit stressed from time to time when we have a lot on. In fact, we need a bit of stress to perform at our peak – the boost in hormones that stress brings can help us keep going in a marathon or give off our best in an important presentation.
The science of stress
When you’re stressed, your body produces hormones – chemical messengers which travel around your body, causing a reaction in other parts of the body. These include cortisol, which (among other things) makes more glucose for energy available to your brain and muscles.
Adrenaline, the so-called ‘fight or flight’ hormone, is also produced when you’re under stress. Adrenaline is really helpful if you need to get out of a threatening situation – it makes your heart beat faster and sends more blood to your muscles and brain. You also produce it when you’re excited – which is why dry mouth, clammy palms, racing heart and butterflies in your tummy are common to both fear and excitement.
Adrenaline is both a hormone and a neurotransmitter, which allows nerves to communicate with each other. It’s part of the sympathetic nervous system, which has overall control of your body’s reactions to stress. Your parasympathetic nervous system, by contrast, is sometimes known as your ‘rest and digest’ system – when you’re relaxed, the parasympathetic nervous system allows your body to focus on long-term maintenance, like digesting food.
How can stress affect your health?
Occasional bursts of stress hormones won’t do you any harm. However, for many people, stress tips over to the stage where your body is constantly on high alert. Long-term exposure to these stress hormones can disrupt almost all your body processes. Of course there are the mental effects – anxiety, sleep problems, poor concentration, low mood.
But too much stress can affect your physical health too – It’s linked with an increased risk of headache, high blood pressure, heart attack, stroke, weight gain, type two diabetes and more.
The gut-brain connection
Your brain contains no fewer than 100 billion nerve cells (called neurons). That sounds impressive, but then, the brain is all about nerve cells. After all, the main role of the brain is to transmit messages between nerve cells.
Few of us connect the gut with nerve messages – yet there are 500 million neurons in your gut nervous system (also called the enteric nervous system). These nerve cells connect to your brain via the gut-brain axis.
The release of adrenaline as a result of stress can stimulate unhealthy bacteria to reproduce.
Research has shown that your gut microbiota – the billions of bacteria (as well as viruses and fungi) that live in your gut – has a fundamental impact on your body’s immune system, which fights off invaders. In fact, 70-80% of your body’s immune cells are located in your gut. The lining of your gut is just a single cell thick – that’s all that stands between the food (and accompanying germs) that you take in and your inner body.
This community of gut bacteria can affect levels of inflammation, which in turn may affect your risk of dementia, stroke, gut conditions such as Crohn’s disease and ulcerative colitis.
The gut-brain axis works both ways, with millions of messages sent from gut to brain and from your brain to your gut. Your gut nervous system is closely linked to both your sympathetic and parasympathetic nervous systems.
How your gut microbiota can influence your mood
The first real proof of the power of the gut microbiota on the brain came from animal studies. In 2011, a group of researchers changed the gut bacteria make-up of a group of typically shy mice: their behaviour changed completely.
Later, the same scientists carried out gut bacteria swaps between two groups of mice – one naturally anxious, one naturally bold. This single step of changing their gut microbiota caused the two groups to switch behaviour, with the timid mice becoming more brave and active.
Gut microbes play a role in producing many of the neurotransmitters that influence your brain’s function. For instance, the bacteria in your gut make about 95% of your body’s serotonin, which plays a major part in mood. Having more healthy microbes in your gut can help them crowd out harmful bacteria.
How does stress impact the gut?
Your gut and your brain are closely linked – far more closely than we realised just a few decades ago. This communication system is known as the gut-brain axis. The connections come about through a variety of direct nerve links and hormones. Interestingly, hormones released in the gut play a role in the cross-talk, meaning your gut can affect your brain as well as the other way round.Stress can have a major impact on your gut microbiota. It can also affect blood flow and absorption of nutrients from the gut; the rate your body produces digestive enzymes and other secretions; and how efficiently your gut moves food through your digestive tract.
And there’s now good evidence that your gut microbiota can affect both the release of gut hormones and how they work.
So where does stress fit in? Well, anyone who has ever had ‘butterflies in their tummy’ or felt ‘sick with anxiety’ knows exactly how much your brain can affect your gut. Being off your food, or feeling endlessly hungry, are common symptoms of depression.
The close connection between your gut microbiota and your physical and mental health is why it’s so important to maintain a healthy gut microbiota. There’s now clear evidence that stress can affect the make-up of the bacteria in your gut. A study that looked at frontline healthcare workers during the pandemic showed that:
- Going through repeated stressful experiences disrupts the balance of gut bacteria – so-called ‘dysbiosis’.
- Gut dysbiosis persists for many months after the stress has settled.
- Some of the bacteria affected are closely linked with mental health problems.
How do you fight stress?
Given how closely your gut and the rest of your body are linked, it’s hardly surprising that being kind to yourself will also benefit your gut. Tried and tested solutions include:
1. Take time out to be kind to yourself
This doesn’t need to involve expensive spa days. Just carve out some ‘me time’ – whether it’s half an hour on your own with a good book, or a regular date with a warm bath, some candles and soothing music.
2. Concentrate on the things you can control
Make a list of all the biggest stresses in your life. Then break them down into elements you can control and elements you can’t. Set yourself goals for the aspects you can make a difference to – whether it’s ensuring you book a holiday or saying no when someone tries to take advantage.
3. Get moving
Physical activity is one of the most proven ways to reduce stress. Your body produces natural feel-good hormones, called endorphins, when you exercise.
4. Be mindful
Mindfulness is all about focusing on the here and now – being ‘fully present’ rather than letting your mind dart from worry to worry. It takes time and practice, but there’s good evidence that it can help reduce stress.
5. Take breaks and breathe
Even a couple of minutes every hour to stop, breathe in slowly through your nose and out through your mouth can help you rebalance.
6. Give alcohol a miss
Don’t be tempted to numb the pain with alcohol. It may feel as if alcohol makes it easier to cope. But alcohol is actually a depressant, and it’s easy to become dependent. If this happens, your levels of anxiety will increase as your blood alcohol levels come down, leading to a vicious cycle.
7. Be good to your gut
This aspect is so important that we have a whole section on it!
How to reduce stress and improve gut health
Given what we know about the impact of your gut on stress, and vice versa, it’s hardly surprising that getting your gut in good shape is key to reducing (and coping with) stress.
The media is full of headlines about rising levels of stress and mental health problems. While there are lots of factors at play, diet undoubtedly plays a part. The wider the variety of foods you eat, the healthier your gut microbiota. Ultra-processed food, and a limited diet, play a particular part in reducing gut health. In the last 50 years, the rise of processed foods and industrial farming practices have meant that that 75% of the world's food originates from just twelve plants and five animals.
Vegetables and fruits all contain different chemicals, nutrients and types of fibre. Each of these supports and encourages different microbes. Try and aim for 30 different types of fruit, veg, nuts, seeds, pulses and legumes in your diet every week.
Prebiotics are foods that healthy bacteria thrive on. Good diet sources include onions, leeks, garlic, mushrooms, savoy cabbage, oats, barley, asparagus, flax seeds, apples and bananas.
Probiotics contain large quantities of healthy microbes, which can tip the balance of your gut microbiota to a more positive state. So-called probiotic foods include sauerkraut, live yoghurt, kefir, kombucha, miso, tempeh, kimchi and sourdough bread.
Taking a regular probiotic supplement can be a really effective way to top up your good bacteria. However, it’s important to remember that not all foods marketed as probiotic have the same evidence behind them.
References
Stress and glucocorticoid receptor-dependent mechanisms in long-term memory: from adaptive responses to psychopathologies
Charles Finsterwald and Cristina M. Alberini*
Physiology, Cortisol
Lauren Thau; Jayashree Gandhi; Sandeep Sharma
Adrenal hormones
Neuroanatomy, Sympathetic Nervous System
Mark N. Alshak; Joe M Das.
Prolonged Stress Leads to Serious Health Problems: Preventive Approaches
Naila Rasheed
The human stress response
Georgina Russell 1, Stafford Lightman 2
The Human Brain in Numbers: A Linearly Scaled-up Primate Brain
Suzana Herculano-Houzel1,*
Nonruminant Nutrition Symposium: Involvement of gut neural and endocrine systems in pathological disorders of the digestive tract
J B Furness 1, D P Poole
Gut hormones in microbiota-gut-brain cross-talk
Li-Juan Sun,1,2 Jing-Nan Li,3 and Yong-Zhan Nie1
Gut microbiota, metabolites and host immunity
Michelle G Rooks 1, Wendy S Garrett 1 2 3 4
Gut feelings: the emerging biology of gut–brain communication
Emeran A. Mayer
The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems
Marilia Carabotti,a Annunziata Scirocco,a Maria Antonietta Maselli,b and Carola Severia
The intestinal microbiota affect central levels of brain-derived neurotropic factor and behavior in mice
That gut feeling
Dr. Siri Carpenter
Gut hormones in microbiota-gut-brain cross-talk
Li-Juan Sun,1,2 Jing-Nan Li,3 and Yong-Zhan Nie1
Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options
Peter C Konturek 1, T Brzozowski, S J Konturek
Gut hormones in microbiota-gut-brain cross-talk
Li-Juan Sun,1,2 Jing-Nan Li,3 and Yong-Zhan Nie1
Stressful events induce long-term gut microbiota dysbiosis and associated post-traumatic stress symptoms in healthcare workers fighting against COVID-19
Fengjie Gao,a,b,c,1 Ruijin Guo,d,1 Qingyan Ma,a,b,c Yening Li,a Wei Wang,a,b,c Yajuan Fan,a Yanmei Ju,d Binbin Zhao,a Yuan Gao,a Li Qian,a Zai Yang,a Xiaoyan He,a Xiaoying Jin,a Yixin Liu,a Yuan Peng,a Ce Chen,a Yunchun Chen,a Chengge Gao,a Feng Zhu,a,b,c,e,⁎ and Xiancang Maa,b,c,⁎
