Should you try fasted training?

What is fasted training and how can you try it safely?

Posted by for Strength

Fasted training: a fitness trend or a great way to increase your endurance? We asked three experts about the benefits of fasted training, and how to do it safely.  

Over the first lockdown, I got into a habit of taking a morning 7km walk. I’ve never been a morning person and so always felt sluggish and lethargic hauling myself out of bed, and even worse once I’d wolfed down whatever quick-fix breakfast was at hand before hitting the pavement.

When I complained to my boyfriend that I was sick of cereal sloshing around in my stomach and toast that just made me hungrier, he suggested trying fasted walking: not eating anything at all before exercising.

Packing just our water bottles and a protein bar in case we got ravenous on the way, we set out for our first fasted walk. I wasn’t tired or even hungry. In fact, I was surprised at how much more energised I felt. My mind seemed clear and focussed, and the endorphin high set me up for the rest of the day. 

Fasted training – and cardio in particular – has become a popular fitness world training trend. But there’s actually a lot of science to it. And it seems it is still increasing in popularity. 

Alex Ruani, a doctoral researcher in nutrition science and chief science educator at The Health Sciences Academy tells Stylist that the academy currently teaches a dedicated fasted training course as part of their 15 certifications.

However, undertaking any fasted exercise is something I’ve always been – rightfully– cautious of. I know how important fuelling and nourishing my body before and after exercise is, so I consulted three experts on how to fasted train safely. 

What happens to your body during fasted training?

“When your body is in a fasted state, your blood glucose (sugar) levels drop,” explains Dr Naveen Puri, associate clinical director at Bupa Health Clinics. “The main way the body produces energy is by using blood glucose, which comes from carbohydrates. If you have no blood glucose in your system, your body enters a ketogenic state.”

This ketogenic state occurs when your body uses ketones - chemicals produced in the liver when breaking down fats - for energy to fuel your workout instead of carbs. As a result, your body burns stored fat.

What kind of training is fasted training suited to?

“Fasted training is better suited to lower intensity exercise that keeps your heart rate at a steady pace,” Dr Puri says, such as walking, swimming and cycling. According to Dr Puri, this is because the decrease of blood glucose levels during a fasted state can cause fatigue, a decline in cognitive function and in some cases, fainting.

Therefore, it probably isn’t best to take on a heavy lifting session if you haven’t eaten yet, but a moderate cardio class or bodyweight workout would be fine. 

What are the benefits of fasted training?

A study in the British Journal of Nutrition showed up to a 20% increase of fat burned in a fasted cardio workout. Other research supports increased endurance when performing cardio in a fasted state.

However, while endurance can improve in fasted steady state cardio workouts, high intensity and other interval training can be less effective. “These types of exercises require carbs for optimal performance – so intense exercise like HIIT will feel more difficult even at a lower intensity level, and likely impact performance,” explains Myprotein’s resident dietician Claire Muszalsk.

What should you be mindful of when fasted training?

Optimal performance is often seen when you consume some carbohydrates one to two hours before your workout. “Therefore, when fasted training, the drop in blood sugar levels may trigger existing health conditions and lead to unwanted complications arising,” says Dr Puri.

Many other factors, such as menstruation, dehydration and even drinking too much the night before fasted training, can also affect how your body responds to the decrease in blood sugar levels.

“We always advise a sustainable exercise approach that you can apply safely in the long term, rather than delving into exercise plans that offer a quick fix, where the longer-term impacts are not as well understood,” says Dr Puri.

Muszalsk also points out another potential drawback: muscle loss. “When glucose isn’t available as fuel, we hope our bodies will use fat for energy – but there is also the potential for muscle breakdown as well,” she says.

To prevent this, she advises ensuring at least 30% of your daily calories come from protein, and re-fuelling after a fasted workout with at least 15 to 30 grams of high-quality protein in a meal or shake. 

How can you recover properly from fasted training?

It’s important to tailor your nutrition and recovery to the type of training you’ve undertaken, Ruani says. “If you’ve completed a fasted strength training session for over an hour, you will need both carbs and protein in your recovery meal. For every gram of protein, you should aim for about three to four grams of carbohydrates to refuel.” She recommends eggs, yoghurts, oats and berries to help with muscle repair and recovery

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Images: Getty

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