What is fasted cardio?

The fitness industry is guilty of constantly peddling “tricks”, “hacks”, and “shortcuts” to us lowly consumers because we want results and we want them right now. One of the supposed optimal fat loss methods that has gained popularity in recent years, is fasted cardio. This is where you would opt out of eating breakfast before your morning run with the idea that it would accelerate fat loss. On the surface, this seems to make a lot of sense, because after sleeping for 8 hours, your glycogen/carb storages that you use for energy are low, and thus, you would turn to stored fat to use as fuel resulting in quicker fat loss. Also, your insulin levels are typically low in the morning since you don’t have many carbs in your system. When insulin levels are high, it impedes fat loss, so the lower levels will help make fat loss easier. So, is there merit to this? Is it better than training at a fed state? Let’s look into what the latest research has shown

Does fasted cardio work?

In 2017, two researchers, Daniel Hackett and Amanda D. Hagstrom, conducted a meta-analysis of fasted vs. fed cardio and its effects on fat loss. In full transparency, it only reviewed five studies, and there is still a lot more research to be done before we can be completely confident in their effects.

What they found was that DURING exercise, yes, you burn fat at a higher rate, but, over the course of a day and several weeks, the total amount of fat you lose was the same as people who were fed given that the calories are equated and they are in a deficit. The reason being is that it has been shown that if you use a particular fuel source during a bout of exercise such as carbs or fat, you will burn less of that substrate over the course of the rest of the day. So, when you are burning large amounts of fat during a fasted cardio session, you are going to burn fat at a much slower rate over the rest of the day after the session. Conversely, if you ate an apple to ingest carbs before your workout as a fuel source, then the rest of the day you would be burning carbs at a slower rate than during your training.

In addition to the substrate explanation, after completing your fasted training session, you are now going to be consuming your food for the day and if that amount is equal to what you would be having the day of a fed session, then it would have the same net result. So even though you are burning more fat acutely during your fasted session, it seems to have the same overall effect. The most important factor for fat loss still remains to be the overall caloric amount over a given day.

Should you do fasted cardio?

Ya know, sometimes I don’t feel like waking up an extra 30 minutes earlier to make breakfast. That’s a perfectly valid reason to do fasted cardio. Maybe it makes you feel better. Maybe you are completely comfortable with your appetite that training fasted doesn’t bother you. Hey go for it! It’s awesome that you’re moving in the first place! However, it is not better for fat loss compared to those who eat breakfast. So, per usual, do what you enjoy and can stick to and with patience and consistently, you’ll see awesome results, breakfast or not!


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  1. https://www.mdpi.com/2411-5142/2/4/43/htm
  2. https://www.ncbi.nlm.nih.gov/pubmed/21411835