It happens like clockwork. Every few months, hundreds of videos promising to boost your gut health flood TikTok. Shots of olive oil, stewed apple and sweet potato soup have all gone into the algorithmic blender with the promise of feeding your microbiome.
But with the line between experience and evidence as blurry as your Christmas party camera roll, it can feel hard to separate the recipes for good gut health from the recipes for a messy kitchen. So when we heard there was an evidence-based gut health hack that didn’t involve dirty dishes, we were all ears.
Exercise is being talked about in gut-health circles with the kind of enthusiasm usually reserved for stool samples. Not only can a sweat session support your microbiome, suggests the research, but the relationship works both ways – with a healthier gut, in turn, making you feel more motivated to exercise (which then improves your gut health…you get the idea).
‘When performed with correct form, exercise has been shown to improve both the diversity and strain of your gut microbiota,’ says Dr Stacy Sims, a female physiologist and nutrition scientist who specialises in female performance.
‘We also know that a greater gut diversity is associated with a dominant strain of microbiota – small microorganisms that live in your microbiome, in your digestive tract – known as Bacteroidete, which is responsible for increasing lean muscle mass and reducing body fat.’ And if you’ve just taken the trouble of learning to pronounce ‘Bacteroidete’, this bit of bacteria is just the beginning.
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How are your gut, cortisol and fitness related?
That a well-functioning gut can help curb your cortisol (your stress hormone) isn’t news; the mind-gut connection has earned more headlines than Harry and Meghan and there are now whole food groups dedicated to boosting your brain via your gut (see: kombucha and co). But if managing your stress can make you kinder to your colleagues, it can also make you fitter. ‘Healthy gut microbiota help modulate oxidative and inflammatory stress,’ says Dr Sims, on the mechanism behind the mind-gut connection.
This matters, since keeping a lid on cortisol is a precursor to exercise adaptation – the technical term for your body’s physiological response to training. ‘Cortisol signals to your blood vessels to constrict, restricting blood flow to your muscles and depriving them of the oxygen and nutrients they need to refuel,’ adds Dr Sims. ‘So when your cortisol levels are too high, your muscles can’t repair themselves, which they need to do in order to grow.’
Does gut health increase motivation to exercise?
But perhaps the most powerful piece of evidence for the gut-muscle connection is that it can influence your desire to get up and do a workout in the first place.
A study published by the University of Pennsylvania School of Medicine found that ‘good’ gut microbiome creates molecules called metabolites; these metabolites are thought to act as your body’s very own Mr Motivator, stimulating the sensory nerves in your gut responsible for enhancing activity in the part of your brain that controls drive.
Thought to, because the research wasn’t conducted on humans. But both Dr Sims and Shrushti Shah, a PhD candidate in Kinesiology – whose study ‘How fit is your gut microbiome?‘ was published last March – point out that metabolites aren’t the only motivating force you gut is responsible for: 90% of your serotonin – a neurotransmitter that plays a big part in motivation to exercise – is created in your gut.
‘If your gut is a healthy microenvironment for these neurotransmitters to inhabit – characterised by a diverse and rich range of gut microbiota, which exercise can help you achieve –you are more likely to have the desire to exercise.’
Of course, much like the festive fake tan, the ‘too much of a good thing’ adage applies. ‘Exhausting or long-lasting training can actually have a negative impact on your intestinal microbiota,’ adds Dr Sims. ‘The subsequent “dysbiosis” – or imbalance – this creates could then lead to an impaired immune response.’ Meaning your gut will be less able to protect itself from bugs.
The culprit? Our old friend, cortisol. The increase in cortisol levels that overtraining delivers can cause intestinal permeability, also known as ‘leaky gut’. While your gut is semi-permeable to allow micronutrients to pass through your intestinal walls and into your bloodstream, cortisol breaks these walls apart, allowing toxins, microbes and undigested food particles to invade your bloodstream. Cue an onslaught of undesirables in the form of bloating, gas or diarrhoea.
Exercise isn’t everything, of course. The make-up of your microbiome is influenced by everything from the food you put on your plate to the number of candles on your cake, but as interventions go, it’s among the most accessible. While conducting her research, Shah found that ‘moderate exercise’ increased both the richness and diversity of gut microbiome in adults, irrespective of their body weight; walking and cycling count, but hoovering and gardening do, too.
What is the best exercise for gut health?
Here’s the thing: knowing what type of exercise to do, for how long – and how often – can make the difference between a gut that powers you towards your goals and a gut that leaves you running towards the toilet. With that in mind, we read the research and recruited the health of salaried gut health professionals to bring you a guide to making your microbiome work for you.
What it does: The bigger question with strength training is what it doesn’t do. Now, to a list of mind-body benefits that includes bone-strengthening, memory-enhancing and skin-supporting (yes, really), you can add microbiome-boosting.
A 2021 study published in the journal Frontiers in Immunology found that strength training can increase both the abundance and diversity of your gut microbiota, while enriching the bacteria responsible for producing (anti-inflammatory, neuroprotective, immunity-supporting) short chain fatty acids.
Strength training also improves your ratio of the two main strains of gut bacteria: Bacteroidetes and Firmicutes; the former responsible for developing your lean muscle mass, the latter responsible for extracting and storing fat from the food you eat, increasing your body fat in the process.
How to do it: Dr Sims suggests performing a series of four to eight full-body resistance exercises using either your bodyweight, free weights or gym machines (think: chest press, lunges and deadbugs). Shoot for six to 10 reps of each exercise and take 20 seconds of rest between each set. Once you’ve completed a circuit, repeat it up to four times for a workout lasting between 45 and 60 minutes. Ideally, you’ll repeat this circuit – or a version of – two or three times a week.
What it does: In research which gives new meaning to ‘the runs’, researchers found that the stool samples (them again) of marathon runners contain higher levels of the gut-derived bacteria Veillonella, compared with non-runners.
In the 2019 study, published in the journal Nature Medicine, the concentration of this microbe was higher after workouts, but particularly so after completing a marathon.
Veillonella performs a special kind of magic: not only does it ‘eat’ lactate (also known as lactic acid) – the stuff you produce during a tough workout which can cause the dreaded DOMS; it then turns lactate into a short chain fatty acid called propionate, which is responsible for energy. Credit also goes to Veillonella for keeping you going: the longer you exercise, the more Veillonella you will trigger and the more energy you will generate.
Oh, and if you won’t run for Veillonella, will you do it for BDNF? ‘Endurance training increases brain-derived neurotrophic factor (BDNF) production by producing three types of bacteria in your gut,’ adds Dr Sims. Another over-achiever, BDNF regulates glucose metabolism, increases cardiac muscle contractions and improves circulation – all of which will improve your body composition and speed up muscle recovery post-workout.
How to do it: Here’s the good news: you don’t have a run a marathon to reap the gut health gains associated with endurance training. Dr Sims suggests performing 30 to 45 minutes of continuous jogging, running, cycling, rowing, cross training or swimming once or twice a week. ‘Take it at a challenging pace, but one that you can maintain for the duration of your workout,’ she explains.
3. Moderate aerobic exercise
What it does: Like strength training, moderate aerobic exercise (walking, cycling, yoga) is the health gift that keeps on giving. Shah’s research found that any kind of moderate aerobic activity – the kind you can perform while holding a conversation – reduces gut inflammation via the production of anti-inflammatory metabolites, like butyrate.
In contrast to extended bouts of intense exercise, whereby the majority of your blood flows to your muscles, her research also found that moderate movement directs more blood to your gut.
‘This helps with nutrient absorption, repairing your gut tissue and regulating your immune system via Gut-Associated Lymphoid Tissue (GALT)’, she explains, referring to the tissue containing about 70% of your body’s immune cells that resides in your small and large intestines.
Moderate exercise ensures this tissue stays strong by suppressing pro-inflammatory cytokines and upregulating both anti-inflammatory cytokines and antioxidant enzymes, both of which bolster your immune system and make you less susceptible to catching bugs or viruses.
How to do it: Remember: exercise is moderate when you can hold a conversation. If you have a fitness watch, aim to maintain a heart rate of between 50 and 70% of your max. If you don’t, Google the Rate of Perceived Exertion scale; anything moderate would be graded between a five and eight out of ten. Dr Sims suggests doing a 45-minute walk, cycle, jog or yoga session two or three rimes a week, ensuring you never get too breathless.