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To eat or not to eat before a workout?

A common question amongst the athletic population is whether to consume breakfast before or after an early morning workout. Exercising before breakfast is also known as being in a fasted state, where no food is to be consumed for at least 8 hours (for example, when you wake up after an overnight sleep).

The answer to the above question is quite complex and in fact, the correct answer, like most aspects when it comes to nutrition is…well it depends!

Whether or not to consume breakfast will depend on the duration and intensity of the workouts as well as your individual goal when it comes to both body composition and performance.

It is important to note that carbohydrates are king when it comes to exercise. Carbohydrates are our main energy supply for day to day living and more importantly, to exercise. When carbohydrates are consumed, they are converted into a form called glycogen and stored in limited amounts in both the liver and muscles (1).

Goal: Performance

Recently, it has been suggested that deliberately training with a reduced carbohydrate availability (training low – low glycogen) can enhance aerobic adaptations in the muscles (2). Ultimately, undertaking specific sessions in a fasted state may translate into mitochondrial adaptations where you increase the number and volume of mitochondria in the muscle cells and consequently increased performance (3). However, the evidence regarding whether this translates into a performance benefit is lacking (2).

Nonetheless, undertaking exercise in a fasted state means that glycogen levels are low and therefore performance markers such as power, speed and distance may suffer. Due to a lack of breakfast and depending on the activity/nutritional makeup of the meal the evening before, blood glucose may be reduced, with the lack of muscle glycogen leading to performance decrements.

This is especially important, as on race day, it is vital to consume a high carbohydrate diet before the race itself in order to maximise performance for most people.

Goal: Weight loss

Training fasted has also been utilised as a weight loss strategy. The theory behind this is thought that the body burns more fat for fuel. In reality, yes, you may burn more dietary fat as less carbohydrates are being consumed, however this doesn’t necessarily relate to body fat loss. To lose body weight/body fat, a calorie deficit is required where energy expenditure is greater than energy intake.

Training fasted may leave you feeling overly hungry post workout and therefore you might consume more food than you usually would anyway! Or the lack of food/energy in the training session may cause you to fatigue quickly leading to a lower intensity workout or shortened session where overall energy expenditure is reduced anyway.

So what is best?

A little bit of both.

If you prefer training fasted (such as before work/first thing), aim for the low intensity/ short workout such as a 30 minute recovery run, walk or easy cycle to benefit from metabolic adaptations of training low – burning more fat.

If you have a high intensity interval session or long ride ahead, ensure a moderate to high carbohydrate meal is consumed beforehand for optimal performance and to practice race day fuelling to see what works best for yourself. Additionally, in-race fuelling strategies can also be practiced before race day.

More importantly, if exercising before breakfast, a dose of caffeine such as a standard coffee before a workout is great for a boost. Training fasted may lead to muscle protein breakdown and impaired immune function (4) and therefore it may be worth consuming a source of protein such as a couple of eggs or a protein shake before exercise to protect muscle mass.

In summary, training fasted all the time is unlikely to lead to positive effects for both your health and performance and may in fact lead to adverse harmful effects. Perhaps, choose one to two sessions a week (short and low intensity) to undertake fasted if preferred. Nutrition is individualised, play around with it and see what works best for you.

Thank you to this week's guest blog writer Molly Wisbey.

Molly has recently finished her Masters degree in Sports Nutrition at Liverpool John Moores University after undertaking my BSc in Nutrition at Oxford Brookes University.

Molly shares "I have currently set up my own Performance Nutrition freelance services where I support and coach a variety of clients online. If you are looking for some nutrition help regarding performance or general health, I am currently taking on new clients so please get in touch on any of my social media channels (website in progress). Also, I work for a local football team as their performance nutrition support".

You can find Molly on social media:

Instagram: @fuellingperformancewith_mol Sharing evidence-based nutrition information and recipes.

Twitter: @wisbey_molly


(1) Burke, L., Hawley, J., Wong, S and Jeukendrup, A. (2011). Carbohydrates and training for competition. Journal of Sport Sciences. 29 (Supp 1), S17 – S27.

(2) Impey, S., Hearris, M., Hammond, K., Bartlett, J., Louis, J., Close, G and Morton, J. (2018). Fuel for the work required: A theoretical framework for carbohydrate periodisation and the glycogen threshold hypothesis. Sports Medicine. 48, pp: 1031-1048.

(3) Van Proeyen, K., Szlufcik, K., Nielens, H., Ramaekers, M., Hespel, P. (2011). ‘Beneficial metabolic adaptations due to endurance exercise training in the fasted state’. Journal of Applied Physiology. 110, pp: 236–45

(4) Hulston, C., Wolsk, E., Grøndahl, T., Yfanti, C., Van Hall, G. (2011). Protein intake does not increase vastus lateralis muscle protein synthesis during cycling. Medicine and Science in Sports and Exercise. 43 (9), pp: 1635-1642.

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