When I first began looking into Intermittent Fasting (‘IF’), my first question was ‘but does it cause muscle loss’, but what the evidence I found, and the results I experienced, show that IF does not have to mean muscle loss.
The concern stems from the fact that the health and fitness industry often talk about ‘breaking down muscle’ in order to re-build it – which is actually happening regardless of whether you’re fasting and is a normal mechanism in the body. People also reference the fact that our muscles store energy which is used by the body during a fast, as a reason why fasting leads to muscle loss.
But, there’s a BIG difference between the energy which your muscle store being used as energy versus the muscle itself being used for energy. And, in order of preference, your body will use sugar from your blood first (blood glucose), then stored sugar from your muscles and liver (stored glucose), before moving onto stored body fat (which most us have plenty of, and is exactly what we want to tap into during IF). Not until all of these preferred energy sources have been depleted will your body even think about breaking down your muscle for energy.
In fact, when done properly, IF can help DECREASE the loss of lean-muscle mass whilst chasing a fat-loss goal. A 2016 study discovered that after 8 weeks, alternative day fasting (ADF – a form of IF) and calorie restriction (CR), both saw a significant and comparable difference in overall weight-loss - indicating that both models are a viable weight-loss intervention.
However, when the researchers followed up 24 weeks later (a total of 32 weeks), they discovered that even though the weight re-gain in both groups were similar in total weight, the re-gain in the CR group was mostly fat whilst the ADF actually lost some fat and gained more muscle. This could be attributed to the positive changes to the resting metabolic rate of the ADF group.
For most of you who are fasting for a few extra hours a day beyond your natural sleeping habits, muscle loss is definitely nothing to worry about. Just remember that training and exercise is always beneficial and should be maintained whilst fasting, plus, since intermittent fasting decreases your overall caloric intake there’s no need to reduce your intake any further during your eating hours.
In fact, growth hormone (which is pivotal for long-term health as well as muscle growth) is significantly INCREASED during a longer fast (16 hours +), which could result in an increase in lean muscle as well as fat-loss, compared to CR since food increases the secretion of insulin which decreases the secretion of growth hormone.
I’d love to know what you think and to see your IF results, so please reach out below. Don’t forget, if you want to learn more about how to fast PROPERLY to maximise results and minimise risk of ‘falling off the wagon’, see my Fasting E-Book [here] for everything you need to know before you get started.
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JC and The Nutri-Team