Does Fasted Cardio Really Cut More Fat?

Does Fasted Cardio Really Cut More Fat?

This next piece was brought to you by the one and only Aja Reinhart of Aja Rose Fitness.

An important topic about wether to do cardio in a fasted state or eat your way to victory.


Fasted cardio has been debated in the fitness industry for years

and there are many different opinions on how effective this method is for fat loss.

Fasted cardio is doing cardiovascular exercises after not eating for a period of time (typically after you sleep). Some people believe that fasting before a workout will increase fat loss production and burn more calories during the workout. The rationale behind this is based on glycogen (carbohydrates) and fat storage – our bodies 2 main sources of energy. When the glycogen storage is all used up, the body would need to draw energy from the fat cells, i.e. why many believe fasted cardio aids in fat loss.

Energy has to come from somewhere in the body, drawing on those fat cells would be beneficial for creating a lean and toned body. Some believe it is not that simple, however.

First, we have to understand how the body coverts fat into energy.

There are 2 steps, the first is called ‘lipolysis’. This occurs in our adiposities, (our fat cells) where the body stores fats called triglycerides. Triglycerides are a compound of 1 glycerol (an alcohol) and 3 fatty acids. Cellular energy is created by the breaking down of the fatty acids to access the carbon in its molecular make up. These Triglycerides are broken down and the fatty acids enter the blood stream.  

Secondly, fat oxidation occurs and those fatty acids get taken up by a metabolizing cells. The metabolizing cells duty is to carry energy (the fatty acids) around the body to tissues that need it. For example, a muscle cell. This is where the cell  would further break down the fatty acid in ATP production (energy).

When arguing against fasted cardio there are 2 main points:

1) lower insulin levels in a fasted state


2) lower glycogen levels stored in the muscle as they deplete overnight.

1. Lower insulin levels in a fasted state

Insulin is a hormone produced by the pancreas. It’s main duty is to regulate all the glucose in your body and is a key player in controlling your metabolic rate. When fasting, the body does not need as much insulin to regulate the glucose in the body and this will inhibit the lipolysis process. When inhibited, there will be less fatty acids to use for energy and the breaking down of fat will slow down or stop. When we eat, our insulin levels go back up but then our bodies will use the available carbs as energy instead.

In one study, a fasted group of people were compared to a fed group of people while looking at the insulin levels. The fasted group did burn more fat but by very slim margins. It was concluded that this was due to the limited access the body had to the fat storage to use as energy, though, it was still able to use some fat for metabolic production.

2. Lower glycogen levels stored in the muscle as they deplete overnight  

Another study showed that glycogen levels (which come from carbs) take much longer to deplete in the body overnight if the person has sufficient rest and nutrition. Waking up from a night of rest and going right into fasted cardio, the muscles will still turn to those reserved glycogen stores for energy rather than taking from your body’s fat stores. So if you’re keeping in track with your diet and sleep, fasted cardio may not access your fat storages.

What about after the training session when we then have to eat again?! What happens to the body then and does it still store fat once it’s been used?

It’s important to look at what occurs in the long term to see if this is sustainable for more than just the hour you are training.

Going back to how fat is broken down into energy, other studies have shown that fat oxidation levels were higher in individuals that ate before doing cardio vs. those who fasted for the rest of day. This would advocate for eating before cardio as a method to burn more fat than fasting when looking at the fat loss during an entire day. So even when burning fat was greater fasting before a session, eating before cardio seemed to produce equal loss in fat in a 24 hour period.

Another study analyzed the EPOC (Excess post-exercise oxygen consumption) levels after a workout and found that levels were higher when the subject of the study ate before a workout, as opposed to fasting. This would create a greater ability for the body to perform fat oxidization.  

In the long term, what was the greater benefit to losing fat? Over a two week period, researchers found that there were no statistical differences between fasting before vs. eating before a training session. Both groups lost fat, and very similar fat loss percentage at that.

My conclusion: Do what makes you feel best! Be it fasting before a session as not to feel nauseas or eating a healthy meal so you increase your carbohydrate accessibility, giving you a sense of more energy for the session. Either way, you will lose fat when sticking to the proper nutrition and exercise regime.

- Coach Aja


Daniel Bednarski

Owner and operator of Revival Fitness.

daniel@revivalfitnessonline.com778 533 3285