Fasted Cardio is a hot topic of debate- some believe it is the best way to get rid of the stubborn fat on your body, others completely dismiss it as unhelpful for fat loss, whilst others believe it can actually be detrimental to your lean body mass (the muscle on your body) and potential muscle gains.
Fasted Cardio is the aerobic exercise you would perform first thing in the morning prior to breakfast. Now some do this completely fasted- i.e. the last meal they had was the night before, whereas others take a protein source just before (usually a protein shake and BCAA supplement tablets) in the aim of preserving muscle.
I used to do fasted cardio 1-2 years ago. I would usually do a morning 45minute spinning class at around 6.30am before going to Uni. After the class i would immediately drink a protein shake and on my way out of the gym buy a Starbucks Porridge (there was a Starbucks inside my gym). Now during that time i didn't lift weights- i was more of a cardio girl. I was not too concerned about gaining muscle, as my main priority was losing fat. I mean now i understand that ideally you want to do BOTH (achieved by lifting weights and adding in cardio to suit your goals), but anyway that was what i did. I didn't find that i was low in energy. If i was tired i would drink a coffee in a flask on the way to the gym. I had enough energy to make "personal bests" in terms of km on the spin bike. I also found that because my uni degree was so demanding, waking up early and getting my gym session done at a time where i would usually be in bed worked for me.
Now, 1-2 years later, i have reviewed a lot of the science data that is out there, and listened to a few podcasts by well respected scientists, phd/master graduates and notorious industry figures. Here are some facts I gathered:
- your glycogen stores deplete 50% just from sleeping (overnight fast). Glycogen is a fuel source, and one that will typically be used during aerobic exercise.
-Those that say fasted cardio burns the muscle is stemmed from the idea that if your glycogen level is low, the body will want to preserve it and so will use the fats as fuel instead.
-To burn fat on your body it required liberation of Fatty Acids from the fat tissues which are then transported to the muscle, liver and heart where they are oxidised for energy.
-The critics say that this fat-burning process which requires liberation and oxidation occurs over DAYS and not hours. They therefore say that just by having an overnight fast it would not lead to the body using fats as an alternate source.
-Science studies have shown that as a general rule, if you burn carbohydrates during a workout then you inevitably burn more fast in the post-exercise period. Thus over 24 hours, the ones who exercise in a fed state burn more fat than those that exercise in a fasted state.
-True fat loss boils down to diet as opposed to trying to trick the body to utilise its fat stores. You must review your macronutrient intake of protein, carbohydrates and fats during the day.
-Pre workout and Post workout are the 2 more essential meal times in terms of optimising muscle gains. To lose the pre workout window can be detrimental.
-Studies have shown a greater Nitrogen Loss when fasted. Nitrogen is a molecule which makes up Protein, and so this is evidence or potential detrimental catabolism (breaking down) of muscle.
-If you are still keen on fasted cardio, the recommendation is to keep heart rate between 60-65% max and to ideally take a protein shake or BCAA supplement tablets just before.
-Food is not going to stop you from breaking down fat. It isn't as simple as "i wont eat, then i'll exercise and then i'll lose fat". In fact, when you food there is a "thermic effect" whereby energy is used to break it down, and this creates an afterburn. The afterburn is thus higher when exercising in a fed state, leading to an overall greater caloric burn.
-If you don't have enough energy in the morning to really go hard in your exercise routine then it is not going to really be beneficial.
Hope this helps!