Fasted cardio is either heralded as the best method for dropping fat fast or an activity that’s going to burn through all of your muscle and leave you looking like walking spaghetti. What does the research really say?
Firstly, let’s take a look at why fasted cardio is supposed to be beneficial for fat loss. The theory is that because all of the food you’ve eaten has been fully digested and dealt with, then your body has no choice but to turn to its fat stores for energy. The combination of having lower insulin and glycogen coupled with elevated cortisol and epinephrine (adrenaline) results in greater fat oxidation.
The idea is good, but does it actually hold up?
So far, the research seems to suggest that fasted cardio does actually involve more fatty acids, but doesn’t have a significant impact on the long term results.
A 2012 study looked at the effects of a 60 minute treadmill session on appetite, calorie intake, and resting metabolic rate. It compared both fasted and fed exercise sessions using twelve healthy males between 20 and 26. The results showed that exercise after eating ‘suppressed appetite to a greater extent than fasted exercise’ but there was no significant effect on overall calorie intake or resting metabolic rate.
There are various other studies which conflict whether fat metabolism is greater in a fasted or fed state which makes it hard to draw a definitive conclusion. However, it’s safe to say that whichever does result in more fax oxidation, the difference is going to be minimal.
In terms of performance, a 2010 study found that a fasted state may work better for improving VO2 max, but another study found there to be no statistical difference.
There also seems to be very little difference in terms of muscle breakdown, too. Whilst aerobic activity does enhance muscle protein breakdown acutely due to the body’s desire for amino acids, but according to the non-biased nutritional website examine.com:
“Studies that assess lean mass over time and compare fed to fasted aerobic training really do not note any differences in muscle mass chronically”
The Final Word
With the research available to us currently, it seems like the best course of action is to fit in your cardio sessions whenever suits you best. If you want to go for an early morning run, then so be it. If you’d rather wait until the evening, then go for it. As long as you’re getting the sessions in, it doesn’t really matter when exactly you do them.
It’s not how much fat you burn in a given session, but overall. Just because you do a session in the morning opposed to in the evening doesn’t mean you’re going to lose twice the amount of weight. Fat loss is a lifestyle, not just for a single meal or training session.
My personal suggestion would be to do them when you’re feeling the best and have the most energy. Most people see the best results when they train in the afternoon after their second meal of the day. Though, it’ll depend on your lifestyle and your individual preferences.
If you’re looking to get the best results with your health and fitness goal, then contact me on my website so we can work together for a happier, healthier you.
Author: Alex Reader MSc