<aside> <img src="/icons/light-bulb_blue.svg" alt="/icons/light-bulb_blue.svg" width="40px" /> The human body has evolved to store energy as glycogen and body fat and to use it when required.

So, when you require energy in the absence of incoming food, your body will naturally use these two pathways that are designed to supply you with just that.

Muscle tissue, on the other hand, is not designed to supply you with energy; it’s vital functional tissue that the body acts to preserve.

Still not quite convinced? A real-world study showed that alternate day fasting, only eating every other day, for 70 days caused an 11.4% decrease in fat mass, whilst lean mass (muscle and bone) didn’t change at all.

Like I’ve said previously, in the absence of food, your body processes and prioritises, discarding what is least vital. Your lean muscle is vital, hence why your body has systems in place primed to protect it.

How does this happen? There are a number of physiological responses that seem to make this possible, including a rise in counter-regulatory hormones, such as human growth hormone (HGH).[7]

Nørrelund and colleagues put this idea to the test in a 2001 study, where fasted subjects took an HGH suppressant to see the subsequent outcome on muscle breakdown. Suppressing HGH led to a staggering 50% increase in muscle breakdown, highly suggesting that human growth hormone plays a critical role in the preservation of muscle during fasting.[16]

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