Can fasted cardio improve our gut health?

Tend to get bloated during or after a run? It might be time to take a leaf out of the fasted cardio playbook – unless you’re willing to get to grips with FODMAPs.

For many of us who run first thing in the morning, fasted cardio is a necessity rather than an active choice. If it’s a toss-up between getting up an hour earlier to force down a nut buttery bagel or sleeping until the very last minute before you’ve got to get dressed for a 5k, we’re very much in the latter camp.

Fasted cardio has long been thought to offer benefits aside from the extra hour’s kip. Some studies have found that forgoing a meal before shorter cardio workouts results in a higher metabolic performance. If you’re running having last eaten at, say, 8pm, your glycogen stores will be slightly depleted. That means that within a few minutes of running, your body will begin to use fat as fuel.

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Research has confirmed that we tap into our fat stores as fuel sooner if we run fasted. If we eat breakfast beforehand, we’d be using carbs (unless we ate a keto breakfast, but that’s another story). That’s not a good or bad thing, per se – it just depends on your own specific fitness goals. 

The question we’re interested in is: how does running on empty impact our gut health. Running in itself can lead to queasy-feeling stomachs, and anyone who lives with bloating knows only too well how uncomfortable it can be to move around the office – let alone go for a run. 

Fasting is fine – if you eat fibre later

I grew up running before breakfast and it took a great deal of effort to force down a bowl of overnight oats when I started to run longer. But my stomach is very sensitive; by mid-afternoon, I’m often bloated. Is that because of the fasted cardio?

Dr Megan Rossi, aka The Gut Health Doctor tells Stylist that when it comes to gut health and fasted cardio, “there’s no right or wrong in terms of whether you eat pre- or post-exercise for gut health, as long as you’re getting enough of the nutrients your gut needs.” And when it comes to gut health, one of the key nutrients worth concentrating on is dietary fibre, which tends to come from plant-based foods.

“That means even if you are doing a fasting regime, you’re still getting at least 30g of fibre across the day,” Dr Rossi explains. In other words, run fasted if you like, but make sure you up your fibre intake at lunch and dinner. And that’s not a bad way to look at the day, as loading up on fibre pre-workout probably isn’t a good idea, Dr Rossi warns. 

Keep fibrous breakfasts for non-run days

Fibre tends to sit in the gut, so if you’re planning on running over 5k, you might end up feeling heavy, bloated or needing to make an emergency stop at some point in your session. What you eat before or after a morning run is going to depend on the distance but it’s important to remember that the longer you run, the more blood will move away from the gut and again, that slows down the rate at which that fibre will move.

If you know that you have a sensitive gut and want to avoid feeling like a balloon that needs popping, Dr Rossi suggests thinking about reducing the amount of FODMAP in your diet 24-48 hours before a medium-to-long run. FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols) are types of carbs found in certain foods that are resistant to digestion. Instead of being absorbed into the bloodstream, they go into your intestine where they fuel gut bacteria – producing hydrogen. 

That’s all well and good, but for people with IBS or general sensitivity, that means experiencing digestive symptoms like gas, bloating and diarrhoea.While you definitely don’t want to cut FODMAPs out of your diet unless your GP recommends it, Dr Rossi does suggest that reducing the amount you eat before a run may reduce discomfort.

“FODMAPS are actually beneficial to the gut,” she explains. “They’re prebiotics so they feed the good gut bacteria but it’s not a good idea to load up pre-run on them.” Instead, fill up on fruits and grains when you come back from your run to refuel.

Choosing low-fodmap meals around runs

Common FODMAPs include fructose (fruits and veggies), lactose (milk and yoghurt), fructans (grains like wheat and barley), galactans (beans) and polyols (sweeteners). A low-FODMAP pre-run breakfast could be a chia pudding or bowl of overnight oats made with oat or almond milk, or some kind of egg situation.

If running on an empty stomach works for you, fab. You’re not doing your gut any damage by skipping breakfast so long as you make an effort to get that dietary fibre in throughout the day. But if you do need fuel to run and you experience symptoms of bloating or discomfort, then experimenting with low-FODMAP breakfasts and snacks may help. 

Of course, if you think you have IBS, then it’s worth chatting with your GP. If you want to know more about FODMAPS and where to find them, check out Dr Rossi’s first book Eat Yourself Healthy. 

Check out our Run It By Megan Q&A with Dr Megan Rossi over on the Strong Women Instagram page (@StrongWomen).

Images: Getty

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