Does fasted cardio help with weight loss?


You may have heard or read that fasted cardio is superior for losing weight and fat and therefore wondered whether this is true. This article provides the science behind fasted cardio and some need to knows and top tips for optimising your benefits from fasted cardio.

Where did the theory of fasted cardio come from?

The idea that avoiding carbs or fasting prior to cardio was borne from research in the 1970s showing that if you fuel your body with more carbohydrate’s pre-exercise, then during exercise you will predominantly utilise carbs for fuel, rather than fat (Alborg and Felix, 1976). It is important to note that the preferential use of carbs or fat for fuel does not determine fat loss – what is always required for fat loss, is a create a calorie deficit.

Additionally, it has been shown that if you do utilise more fat for energy during a cardio session, then post exercise session you will subsequently utilise more carbs for energy over the next 24 hours – and vice versa (Paoli et al. 2011). Implying, that overall, the net difference between utilising fat or carbs for fuel is zero!

Is fasted cardio superior for weight loss?

In a nutshell, no! A review of five different studies concluded that fasted cardio does not increase weight loss and fat mass loss (Hackett and Hagstrom 2017). When calories were matched, there were no significant differences in body or fat mass between the groups that did their cardio fasted or fed.

Will I improve my weight loss from fasted cardio?

This will come down to you as an individual. Firstly, it is important to note that mechanistically, fasted cardio is not superior for weight loss and fat loss. However, if you find that doing your cardio fasted facilitates you being in a calorie deficit, then obviously it will improve your weight loss. For instance, if you do not start eating until a later time and this results in your eating less overall, then it will contribute to you being in a calorie deficit.

However, if you find that doing cardio in a fasted state reduces your capacity to work out properly and you feel fatigued, then this may be detrimental to your weight loss and fat loss since your overall energy output may be decreased.

Is fasted cardio right for you?

Some individuals prefer to do cardio in a fasted state. They may feel more energised, preferring not to eat pre workout, or it may simply not fit with their schedule. For example, if you exercise first thing in the morning after waking, you may find that it is not possible to fit a meal into your schedule. If any of these reasons or similar resonate with you, or you simply prefer to do your cardio fasted, and it is not at your detriment, then go for it!

However, if you find that you do not enjoy doing your cardio fasted and/or the level of your training suffers because of it, there are always solutions! For example, you might try options such as some amino acids and/or some fruit 30 mins pre training. Steve has formulated a pre-training formula called PFORM Active, which he utilises with many of his clients prior to exercise to support performance.

You also want to consider your individual situation, which will be discussed more below.

Are there any risks to doing fasted cardio?

Fasted cardio may be a risk, if it is not suitable for you. For example, if you are pregnant, fasted cardio would not be recommended and if you have any health indication, you would be advised to speak with your doctor first.

Additionally, if you are especially lean, have issues with hypoglycemia (low blood sugar) or are type 1 diabetic fasted cardio may be detrimental.

Essentially any risks will depend upon you as an individual, your health, weight, daily energy intake, training volume, overall lifestyle and the length of fasting you are undertaking pre cardio.

For example, if you are very overweight and go for a walk fasted upon waking, this is not comparable to someone very lean, doing a high intensity training session, who at their last meal 18 hours ago. If you are unsure whether fasted cardio poses a risk for you, we are happy to support you with our team of clinicians.

Top tips for optimising fasted cardio

1. Practise being fasted first:
If you have never experienced going longer periods without meals, then it would be helpful to trial a few sessions of extending periods without food to see how it feels. For example, you could try a 12 hour window of fasting – have your last meal completed by 8pm and not eat your breakfast until 8am the following day. This will allow you to see how your body feels being in this state and your levels of energy.

2. Gain a grounding in fitness first:
If exercising hasn’t been your thing, why not make it your thing? You could start by introducing some daily walking and try a free online class of your fancy. If you already do some walking, why not try upping your step count and introducing something new.

3. Follow a nourishing diet
Consuming a nutrient dense diet is one of the most important factors in your status of health. Whatever your situation, if there are benefits that you can potentially gain from fasted cardio, being at your healthiest will help you reap them!

4. Choose low intensity exercise:
Fat is the preferred fuel for generating energy at lower intensities of exercise. Trial a fasted morning walk, or some light yoga first thing in the morning before breakfast. Depending on your level of fitness and you as an individual, a light jog or cycle could also work.

5. Listen to how you feel:
Do you feel energised and strong doing your morning run on an empty stomach? Or is it a struggle to get out there and do you not perform at your best? Tune into what works for you.

6. Avoid stress:
As mentioned, both fasting and exercise are stressors, so consider your whole situation and lifestyle. If fasted cardio is a must for you and stress is something you need to be aware of, then consider other places in your life that you can reduce stress.

7. Don’t be afraid to adapt:
If you have been doing fasted cardio for a while and it works well for you, don’t be afraid to throw in a few sessions with some food beforehand and see how your body responds. Likewise, if you’ve always wondered what it would be like to try an exercise session fasted, then throw one in!

8. More isn’t necessarily better:
When it comes to fasting and exercise, both separately and combined, more is not necessarily better. The dopamine high from fasting may mislead you to think otherwise! So be mindful of the volume that you are doing of them and whether this is optimal for your health goals.

Key takeaways:

Fasted cardio is not inherently superior for weight/fat loss: therefore, if you find that doing your cardio fasted results in you having an overall reduced energy intake, then go for it. However, if it decreases your energy output, then it is not going to aid your weight loss success.

Creating a calorie deficit through your nutrition is the most important factor for weight loss: so, utilise the exercise as an add on and prioritise doing it for overall health, enjoyment and long-term weight loss maintenance. It is much more possible to create a meaningful calorie deficit from the food that you eat.

Personalising your nutrition and exercise program is key for long-term weight loss success: because your program has to be right for you – not for your best friend. Once you have got a nutrition, lifestyle and exercise plan that suits you and meets your needs, you will be able to adhere to it more readily. Consistency and adherence are the must haves for long term weight loss success and maintenance.

Work with a weight loss specialist

Our clinicians specialise in weight loss. All qualified nutrition professionals have backgrounds in the exercise industries and a vast amount of experience coaching clients towards their goals.

Check out our weight loss specialist page, where you can learn more about our services, clinicians and the support and programs that we offer.

If you would like to enquire to work with one of our practitioners, please click the button below: