Fasting ‘F’isiology: October 16

⚔ Fasting-myth-bustin' ⚔

This week’s newsletter will be short ‘n sweet focusing on one of my favorite topics, FASTING 👏 !

Despite its rising mainstream popularity (largely in the form of intermittent fasting), there are still lots of confused peeps out there giving it a bad rap, so today we’ll tackle three of the most common myths around fasting… and maybe by the end of it, you’ll become a convert, too 🤓

Myth 1: “Fasting is dangerous because it elevates cortisol or adrenaline”

Actually: There is a distinction between chronic versus transient increases in hormones

  • For example, exercise is a stressor that elevates stress hormones like cortisol, yet we all generally agree that it’s good for us to exercise regularly... Fasting is a similar acute stressor. The way fasting works physiologically is through the elevation of certain hormones which allow the body to continue fueling itself.

  • The physiology of fasting: As insulin falls, there is a counter-regulatory hormone surge (as the body increases sympathetic tone and produces adrenaline, noradrenaline, growth hormone, and cortisol). This lets the body first break down glycogen (glucose chains stored in the liver) for fuel. Then, there is a period of gluneogenesis (where the body creates glucose from protein). Finally, it gets to burning fat for fuel.

Myth 2: “Fasting is bad because it slows your metabolism down (which will later make you gain weight despite eating and working out the same as before)”

Actually: Fasting works in a way that maintains metabolic rate

  • In a non-fasted state, insulin stops the body from burning fat for fuel (by blocking lipolysis and signaling the body to store fat). So in this situation, since the body doesn’t have access to fat fuel, its metabolic rate is limited to the food calories consumed. Said otherwise, if you consume 2,000 calories and your body has no access to fat fuel due to elevated insulin, then your body can only burn just the 2,000 calories coming from food.

  • In the fasting state, insulin drops and the body can then switch from burning food cals to burning stored fat. So, if you have been fasting and therefore have 0 food cals coming in, then the body will start tapping into stored fat tissue. Assuming there is plenty of fat (and yes, the vast majority of us have plenty), the body does not need to slow down its metabolic rate! So, with fasting, your metabolism stays the same AND you have the added benefit of shedding body fat. You can eat your 🎂 and have it too!

  • NB: should you wish to dive deeper on how insulin resistance makes us fat

Myth 3: “Fasting makes you lose all your (muscle) #gainz” 😱

Actually: This is just how re-building works -- the body needs to first break down excess protein in order to allow for building new protein

  • An analogy: for remodeling a bathroom, Jane Doe has to first remove all the old avocado-green 1970s stuff before she can put in all the new upgraded stuff

  • As explained above in the ‘physiology’ bullet, if you continue fasting past the glycogen-burning phase, the body will then “burn protein.” This “protein” though, is not necessarily just muscle. There is a lot of excess connective tissue and fat that also gets chewed up (visual e.g., the excess skin in people who used to be obese and then lost weight).

  • This process is also part of autophagy (from Greek, meaning ‘self-eating’), when the body deep-cleans and rids of its defective / degraded proteins (i.e. cancer cells and beta-amyloid plaques, which are aggregated proteins in the brain and related to Alzheimer’s and other neurodegenerative disease).

  • Growth Hormone: The body isn’t stupid enough to continue breaking down muscle tissue forever and ever until you turn into a 👻 and vanish into thin air ... You will eventually break your fast and eat again, at which point you body will re-build protein, but in a newly improved and upgraded version thanks to the boost in growth hormone.

Et voilà, myths busted 🥊, hi-yah! If you’ve been converted and want to try fasting, you can find actionable tips & tricks here.

Disclaimer&Such: I never took a science class after high school 🤫

Source: Really just the first 8 minutes of HIH Podcast Ep. with Jason Fung, MD