What’s Up with Fasted Cardio?


I used to believe that I couldn’t train without having something light in my stomach.

My pre-workout snack in my 20s used to be as simple as a banana or slice of whole grain toast with peanut butter. (And if I was feeling fancy and wasn’t pressed for time, I’d drizzle some honey on top of my toast for a bit of extra sweetness.) 

But then I started training first thing in the morning before heading in to work, fuelled by just a cup of black coffee — and I felt great. Much to my initial surprise, I had enough energy to power through the workout and felt energized to tackle the day after class had wrapped up.

Fasted cardio refers to cardiorespiratory exercise performed in a fasted state.

Here’s the deal: When exercising, your body uses two main sources of fuel — carbohydrates (stored in your liver and muscles as glycogen) and fats. If you eat a snack before your workout, your body will use the food you’ve just ingested as the first source of energy.

But if you train first thing in the morning on an empty stomach, your body is going to turn to its reservoirs of glycogen and body fat to fuel your workout — meaning you’ll be burning stored fuel, not the food in sitting in your digestive system.

Some research has shown that when you perform cardio in the morning on an empty stomach, you can burn more fat. A study published in the British Journal of Nutrition found that when subjects were fasted during morning cardio they burned 20% more fat than when they had a meal beforehand. 

Now I’m not suggesting that you go HAM the first time you attempt to train on an empty stomach or exercise when feeling light-headed and go hurt yourself. ALWAYS listen to your body and if it’s telling you to eat, then eat.

Instead, treat the suggestion to train in a fasted state as an experiment — how does it feel the first time you attempt it? Consider giving it a go a few times a week, then break your fast with a wholesome, nutrient-dense post-workout meal. Ideally aim to consume a good quality protein as soon as your workout wraps up in order to best aid the recovery process.

As with most things in life, whether you prefer to train fasted or with a bit of food in your stomach, it all boils down to what works for you. Training in a fasted state isn’t for everyone, but it works for us.

We’ve found that with the training we do most mornings (typically 60mins of yoga, strength training, HIIT or a CrossFit class), we’ve had no issues with training on an empty stomach. We tend to refuel with a plant-based protein shake after our morning training session comes to a close and we feel great. And for us, fasted cardio, coupled with intermittent fasting, has allowed us to reap the rewards of maintaining a lean physique into our 30s.*

A word of caution: If you’re planning to train for longer than 60mins AND at a high intensity, then you may need to incorporate a light pre-workout snack or an easily digestible energy gel or chew within your workout so you can keep going.

*In the spirit of transparency, we don’t weigh ourselves regularly, nor do we own a scale. We gauge a ‘healthy’ weight by how our clothes feel and how comfortable we feel in our own skin. While I’ve never had an eating disorder or officially been diagnosed as having OCD, I know that I’m the type of person who could take weighing myself regularly to an extreme. I have come to learn that stepping on a scale, counting calories or even counting macros could be a potential trigger for me, I don’t like the idea of assigning a number to my self-worth, so I choose to abstain from these activities. Obviously there are situations (like going for a check-up with your GP) where learning your weight is unavoidable, but these instances have served more as opportunities to gauge where I’m at with my weight with a simple data point versus a number to measure my self-worth against. x

MovementKatie Carroll