Do you prefer to train fasted or not? We go into the difference between either method on a physiological level and reveal some of the potential benefits. To provide an umbrella to this concept, both ways are fine to implement, it is how you feel with using either method that will influence what is best for you.
Training fasted means you have not consumed anything of caloric value prior to training. However, there is some debate whether you can consume minimal calories (e.g. 20) and still be fasted. It just depends how much energy you can ingest before your body recognises it as food and commences your metabolic pathways and digestion. Some food items that contain little to no caloric value that are fine to have while fasted are black coffee, tea (with no sugar or milk) and some BCAA’s (if it’s of very low caloric value).
The idea behind training fasted is that you’re forcing your body to use the stored glycogen i.e. the stored energy you have. As carbohydrates are generally your body's preferred source of fuel, once you’ve used that during your training session - if it's intense enough - then it will use fat as its next fuel source. It's then thought you might be burning more fat as a fuel source because you’ve used all of the glycogen i.e. stored carbohydrate. Another benefit of fasting pre workout is that it might be easier on your gastrointestinal tract i.e. your tummy, as there will be less volume in there, lessening the chance for potential discomfort.
A potential disadvantage to this method is that you may feel lethargic or tired as you haven’t had any food to fuel up for the session. This may mean that you might not be lifting as heavy as you potentially could in a functional session or may not be able to run that 500m buy-out as quickly as you liked because you don’t have anything left in the tank.
Eating before training has a few purposes. As carbohydrate is the preferred source of fuel for the exercising muscle, consuming carbohydrates before a workout can fuel up your muscles for performance.
A benefit to this is that your muscles have more capacity to work. This may translate to more output such as doing a few extra reps or lifting slightly heavier. You may also feel like your performance improves with your brain having a perceived increase in capacity via the carbohydrate. Therefore, the train of thought is that if you had an increased capacity to do more work, you may burn more energy (calories) compared to training fasted.
Ultimately, it’s a matter of personal preference to train fasted or not. Trial and error is a great way to see which style best suits you and your training schedule.