The Truth About Fasted Cardio
You may think you need food to fuel your workouts, but you are wrong. For years now the advice has been to load up on carbohydrates before exercise, but more recently this has been questioned. Consuming carbohydrates before exercise can increase performance in certain fields like sprinting and sports that use power movements, but it also stops the body from using stored body fat for energy which means you are less likely to reap the reported fat burning benefits.
I have trained fasted for four years now, and for three of those I was a competitive sprinter, competing nationally in the 100m, 200m and 400m. I hate the feeling of training with food in my stomach; I feel heavy, bloated and lethargic. When competing I followed the ‘train-hard, race-easy’ principle. I trained fasted, allowing my body to become as efficient as possible at maximising energy reserves and then at competitions I raced with high carbohydrate stores to maximise performance.
What does fasted mean?
Over the course of the day you go in and out of fed and fasted states. The fed state lasts for about four to six hours after your last meal. Insulin is released to lower your blood sugar, proteins and fats are absorbed by the digestive system and glucose is transported to the muscles to be used as energy (glycogen).
Six hours after eating you enter the fasted state. Glucagon is released to keep your blood sugar at normal levels. Your body starts to break down adipose (fat) tissue into free fatty acids, which can then be converted into a form of energy known as ketone bodies. Insulin inhibits the breakdown of fatty acids into usable energy, so essentially when you start eating again your body stops its fat-burning mechanism.
This makes perfect evolutionary sense; when food wasn’t as readily available as it is today, holding on to stored body fat was crucial for our survival. Now food is in almost constant supply but our bodies are still physiologically the same as they were tens of thousands of years ago. If we eat all day, we never tap into our bodies’ natural ability to burn stored body fat for energy. Fasted exercise is a way of maximising this potential.
Fasting cardio can help you to become more metabolically efficient
Studies demonstrate that a bout of aerobic exercise performed in the fasted state as compared with non-fasted state increases the reliance on fat and subsequently reduces the reliance on carbohydrate as fuel during exercise, with several publications showing that fasted exercise oxidises (burns) around 20-30% more fat.
Being less dependent on carbohydrates for energy is a good thing, you will end up feeling less hungry because your body knows how to tap into fat reserves for energy, rather than being dependant on the food you eat. Not craving high energy foods all day can be a big help when you are trying to lose weight and be healthier.
Long term dependence on carbohydrates can lead to Insulin resistance which is one of they are driving factors in metabolic disease and type 2 diabetes.
How to implement fasted cardio
I suggest starting your fasted training with less intense aerobic activities, such as walking, jogging, swimming or cycling.
Initially, your workouts will feel a lot harder than usual when you train in a fasted state, but quite quickly your body will become more efficient as your muscles learn to use less glycogen, which means you will use fatty acids for fuel instead.
Once you get used to it you could start incorporating fasted strength training into your routine, I particularly enjoy fasted strength training – I find it very difficult to train properly with a full stomach and I find my abdominal activation seems to improve with an empty stomach.
Additionally, it is important to mix it up don’t do all your workouts fasted. If you know the workout is going to be more intense and cardiovascular based, I suggest consuming carbohydrates beforehand to help with performance and to prevent low blood sugar which can cause dizziness and nausea.
Equally, the time of day is important. If you are reaching the end of your 16 hour fast, it might be better to top up your glycogen stores before training, unless you are going to do slow, steady state cardio.
Starting an intermittent fasting method like The 2 Meal Day can teach your body to become fat adapted, meaning your fasted training sessions will become effortless.
Common Problems with Fasted Exercise
Issues can arise with fasted training when combined with very low carb diets. The problem with combining fasted training and low carb diets is that you can decrease the body’s ability to utilise carbohydrate. Ultimately, the goal should be ‘metabolic flexibility’ – that is, to prime the body to use both carbs and fat as and when required.
Don’t try and do everything at once, slowly incorporate fasted training into your less intense sessions, and be strategic with your carbohydrate intake. You should be eating more carbohydrates on your training days and less on your rest days.
“Can I have anything before a workout?”
I like to have a strong green tea or black coffee right before my workout. I use caffeine as a performance enhancer, meaning I am very sensitive to its effects. I don’t generally consume it at any other time. I have recently stated experimenting with Form Nutritions “Boost” which I absolutely love!
Fasted cardio is not a magic pill for weight loss, nor is it going to solve all your problems.
It can be an effective tool to implement into your training schedule to improve the efficiency of your body’s ability to use fat for energy – long term this can mean a reduced risk of diabetes, heart disease and obesity.