One of the fastest ways to trigger a heated debate in the gym? Just mention fasted cardio. Everyone has their opinions, but what does the research actually tell us?
Research does show that fasted exercise increases fat oxidation (1). What this means is that, during aerobic exercise, it increases our body's ability to utilise fat stores for fuel. To provide energy to our muscles our aerobic system breaks down body fat into fatty acids. Fasted exercise increases the rate at which this is done compared to glycogen breakdown. This evidence is often used to support the use of fasted cardio for weight loss. Yet, research into the relationship between fasted exercise and weight loss shows otherwise.
Schoenfeld et al. (2014) compared fat loss of a 'fed' group (meal before training) and 'fasted' group (fasted overnight, trained in the morning and then had a meal post-training). Both groups were in a calorie deficit and both displayed significant weight loss at the end of the programme. However, there were no significant differences between the two groups' results (2).
Zouhal et al's (2020) literature review has similar findings: fasted training does equate to increased weight loss compared to 'fed' training (3). This study also shows that the effect it has on performance is often either negative or none at all. They recommend that high-intensity exercise is avoided whilst fasted to maximise recovery particularly when approaching a competition.
A study that indicates that fasted cardio could have a negative impact on weight loss is that of Paoli et al. (2011). Their research suggests, when looking over a 24 hour period, fat burning is slightly higher with fed cardio when compared to fasting (4). Hence, they advise that physical activity is performed after a light meal. As Zouhal et al. (2020) highlighted, consuming food pre-workout will also benefit performance during exercise.
According to research by Escalante and Barakat (2020), not only does fasted exercise have little benefit for weight loss but also poses an increased risk of muscle wastage when exercising in a fasted state. This is a result of muscle protein breakdown (loss of muscle) being in far greater excess to muscle protein synthesis (building muscle). Hence, we can assume that fasted exercise certainly isn't desirable for those looking to build or sustain muscle mass.
Altogether, this brief summary of the literature shows that fasted exercise is not desirable for performance or building/sustaining muscle mass, nor does it have any additional benefits for weight loss. Remember, food is fuel. It provides our body with the energy we need to both exercise and go about our everyday lives. So why not utilise that fuel to improve our performance whilst we train?
What should I eat before I workout?
If you train later in the day, e.g. 4pm, whatever you eat for your lunch will be great fuel for a workout. A mixed meal containing complex carbohydrates, a source of protein and some unsaturated fats is ideal.
60-90 mins pre-workout
Even if you have utilised your lunch/breakfast a couple of hours beforehand, a small snack before your session is always a great idea. You want to be aiming for around 1g of carbs/kg of bodyweight. Ideally this will be a snack comprising of simple carbohydrates which combine fructose and glucose. Fibre and fat wants to be low to increase the speed of digestion.
- A bagel and banana/jam.
- 2 crumpets with honey/biscoff spread.
- 2 slices of soreen and a banana.
- 2 slices of white bread with jam/honey/biscoff spread.
- 4 scotch pancakes with jam.