Weight loss and fat loss are huge topics in the world of fitness, and with health and well-being being even more important to women now than ever before, there is a lot of talk about the best and fastest way to burn achieve this. With 45% of British women admitting to trying to lose weight at any given time, we thought we’d debunk a common question related to this. Is it better to work out fasted (on an empty stomach), or after having something to eat (non-fasted, or ‘fed’)?

In this article, you will hear from our fitness expert, Sport and Exercise Scientist Louise. She’ll talk you through the difference between working out on an empty stomach versus having eaten, and whether exercising fasted burns more fat or calories. Louise will explore the facts and figure out if eating before exercise helps women burn fat more effectively, and share why she thinks hitting the gym with some fuel in your tank might just be the way to go.


Fasted vs Fed – What is the difference?

We use the term fasted when we describe not having eaten for 8 hours or more. 

An example of training fasted could be when you wake up from your night’s sleep and head straight to the gym for a workout, having not eaten anything whatsoever. (Drinking water is acceptable within this fasted definition, but nothing else)

The term fed is used to describe when we have eaten something within the last few hours. The time frame is slightly different to fasted, however. Anything within the last 2-3 hours would be considered fed. 

An example of a fed workout would be having a snack like a banana on the way home from work, before grabbing your workout kit and heading out the door as soon as you’re back. Or, doing some exercise in the evening time, where you have eaten your usual 3 meals throughout the day. 

Now, let’s get a little into the juicy stuff!

What is Fasted Training?

We’ve just found out that fasted training refers to the approach of engaging in physical activity, or exercise, before consuming any amount of food after a period of fasting. 

You’re probably familiar with the term fasting, but did you know that fasting comes in many forms:

  • Intermittent Fasting – A deliberate and decided period of time that you do not consume any food but with a period of time where you are allowed to eat following. There are various forms of intermittent fasting, which you can read about here.
  • Ramadan – Ramadan is the 9th month in the Islamic calendar, which is a holy month of the year. During this holy month, Muslim’s will fast from sunrise to sunset and will only break their fast when the sun has set. Fasting must begin again when the sun has risen. The fasting during this special time is one of the five pillars of Islam.
  • Natural Fasting – This isn’t actually a thing, but is worth mentioning. When we sleep, we are technically fasting. Those weekend lie ins are extra long fasting periods!

Exercising when you are fasted (any of the above), or fasted cardio, is popular because of the belief that exercising on an empty stomach will force the body to burn the fat that is stored, in order to fuel your workout.

It is a common belief that fasted exercise forces the body to use fat as its primary energy source, potentially enhancing fat oxidation, and therefore making the process of burning fat and losing weight faster, or more efficient.

Fat oxidation is the process by which your body breaks down fat to use it as energy

What is Fed (or non-fasted) Training?

Fed exercise, or training after eating provides the body with energy directly from the food that you have just consumed. Let’s say on a weekend, you like to have your lunch and then exercise in the early afternoon, that workout will be powered by the lunch you have just eaten (and also your breakfast, too).

It is thought that this approach improves overall performance, and endurance, and may contribute to burning more energy overall. 

This approach differs from its counterpart, because the fat oxidisation may not be maximised initially like it could be when you are in a fasted state. Yet with the energy from being ‘fed’ and able to perform better during your workout and the amount of energy and calories you burn will actually increase. 

After all, for the average woman, losing weight and fat loss is about striking the right balance of energy expenditure…to achieve this, you must consume less and move more (lower energy intake, and larger energy expenditure).

The science behind how we burn energy whilst exercising

When you start any exercise or movement, your body is incredibly smart and immediately shifts into gear to support this; burning energy to keep this exercise or movement going!

There are two paths in particular that the body will go down, in order to keep burning energy and allowing you to continue exercising.

The first path that the body goes down is burning glucose, and by that we mean, burning the glucose in your blood. So whatever you have eaten that day, or before your exercise – this is what it will use.

This is pretty short-lived, and soon enough the body switches to burning the glucose (glucose being the energy source) stored in your muscles and liver.

Glucose that is stored in the muscles or liver is called glycogen

During the early stages of exercise, and particularly in short but intense bouts of exercise, this is the body’s preferred energy source; it is quicker and easier to convert to produce the energy that you need. This is the energy that fuels exercise that lasts anywhere from 10 seconds to 1 hour and 30 minutes.

(Think HIIT, an hour of resistance training, a spin class, yoga, interval training etc…)

This is an oddly specific time frame, you may be thinking. 

If you continue to exercise past this time frame, your glycogen stores begin to deplete and are quickly running out. So, the body needs to switch it up and do something new in order to keep burning energy and keep this show on the road!

To do that, the source of energy changes. 

To put it very simply, the energy source changes from glucose available within the blood or muscle, to burning fat. 

The body taps into the fat stores and fat molecules are released into the bloodstream to be used for energy.


How does this relate to fasted or fed exercise?

This may come as a shock to you… but in terms of weight loss and fat loss, there is no difference in training fasted versus fed. 

The explanation of how we burn energy may have got you to thinking that you need to exercise fasted, or for long periods of time in order to burn fat (disclaimer: please don’t do that!), but you’d be wrong. 

Research does not support fasted exercise, and especially not for burning fat or losing weight faster.

One study found that exercising fasted made no difference to weight loss or fat loss in comparison to exercising fed, and other research shows that it doesn’t matter if you fast, or if you are fed, the very results are the same over relatively short period of time. 


Louise’s Verdict

As a Sport and Exercise Scientist and Personal Trainer, I certainly have some thoughts on this!

We know that there is no difference in the outcome of losing weight faster, or burning more fat whether you exercise having eaten or not. So the argument of exercising fasted versus fed slightly changes. 

The question then becomes, how do you feel when you exercise fasted, and fed? Which one makes you feel better throughout your exercise?

From my experience, most women prefer to exercise fed. A pre-workout snack or meal goes a hell of a long way in terms of how women experience the exercise. 

The better you feel throughout exercise, the better the outcome you will get. 

Think of your body like a car. Without fuel, it isn’t going anywhere fast. Eating before your workout is like filling up your tank and giving you the energy boost that you need to push harder, and for longer. 

It doesn’t matter whether you are trying to lift more weight, run a little longer, or squeeze in some extra laps in the pool, having that energy reserve from food increases your intensity, quality, and efficiency. 

It is also my belief that women should avoid fasted exercise completely because of the impact that fasted exercise has on hormone balance; but that is a subject for another time!

As a Sport and Exercise Scientist and Women’s Health Specialist, here are my tips:

  • Find out what works for you. Try exercising fasted, and on another day exercising when fed. Note down the differences and make a decision as to which works best for you.
  • Prepare ahead. Have a snack or something prepared that is easy for you to grab or take on the go. Whether you’re a first-thing-in-the-morning exerciser or a straight after-work kind of person, have something prepared to make your life easier. 
  • Time it right. Wherever possible, try to eat at least 1 and a half hours before exercising. Anything sooner may impact your digestion and how you feel throughout the exercise. 
  • Hormones and exercise. If hormone balance is something you struggle with or are concerned about, avoid training fasted completely. 
  • Include carbohydrates. Carbohydrates are the main macronutrient for energy burning. So be sure to include some carbohydrates in your pre-workout snack and meals across the day to fuel your exercise efficiently.

Wondering how to create the perfect pre-workout snack? Find out HERE

“I always train fed. Typically I don’t need a pre-workout snack, however, if I did, my go-to would be a banana dipped in some almond butter”

Why you shouldn’t train fasted

Be mindful of your muscle

Your body needs a constant supply of energy. This is why we need to eat meals across the day. Your muscles need a supply of glucose (a type of sugar that your body makes from the food you eat), to prevent them from breaking down. 

If you exercise on an empty stomach, you run the risk of your body breaking down muscle mass for energy, which is something we want to avoid! 

By eating before you exercise, you are ensuring that your body and your muscles have enough energy to power you through your workout, without impacting any other functions. 


Ensuring that you are exercising fed (having eaten something before going to the gym for example), can help your metabolism beyond simply burning calories. 

It can improve how your body responds to insulin, which helps with blood sugar management. Plus, your body may get better at using the nutrients that you eat for energy, rather than storing them. 

By avoiding fasted exercise, and focusing on fuelling your body for your workout, you’re also helping your body to get better at handling the food that you eat throughout a normal day.


Before you go

There you have it.

Fasted training, fasted cardio, fasted exercise, whatever you’d like to name it, isn’t going to get you to your weight loss or fat loss goal any quicker. 

When it comes to exercising fasted or fed, you’re better off being fed and fuelled and ready to give your all to your workout!

And don’t listen to anyone who tells you otherwise!


The scientific resources behind this article

El-Zayat, S. R., Sibaii, H., & El-Shamy, K. A. (2019). Physiological process of fat loss. Bulletin of the National Research Centre, 43(1), 1-15.

Hackett, D., & Hagstrom, A. D. (2017). Effect of overnight fasted exercise on weight loss and body composition: A systematic review and meta-analysis. Journal of Functional Morphology and Kinesiology, 2(4), 43.

Muscella A, Stefàno E, Lunetti P, Capobianco L, Marsigliante S. The Regulation of Fat Metabolism During Aerobic Exercise. Biomolecules. 2020 Dec 21;10(12):1699. doi: 10.3390/biom10121699. PMID: 33371437; PMCID: PMC7767423.

Rothschild, J. A., Kilding, A. E., & Plews, D. J. (2020). What should I eat before exercise? Pre-exercise nutrition and the response to endurance exercise: current prospective and future directions. Nutrients, 12(11), 3473.

Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014 Nov 18;11(1):54. doi: 10.1186/s12970-014-0054-7. PMID: 25429252; PMCID: PMC4242477.

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