Physiology of fasting


Fasting is always is always an eye-opening experience! And since Christina is now starting her master series with a 2-day water fast, I decided to join her and I am so keen to share with you more!

If you haven’t gone through any type of fasting, reading about it must raise an eybrow, but I hope once you are done you will have a different opinion.

The fasting phases

Life is a cycle continuous cycle, a continious balance and in the same we need to balance between feasting and fasting. This way of living was always an intergral prart of most societies and cultures. The transition from the fed state to the fasted state occurs in several stages.

  1. Feeding – During meals, insulin allows the absoption of glucose into tissues such as the muscle or brain for energy. Excess glucose is stored as glycogen in the liver.
  2. The adaptation phase – Between 6 to 24 hours after starting your last meal glycogen (the liver) releases glucose for energy. These stores last for 24 hours.
  3. Gluconeogenesis – after 24 hours and for around 2 days, the liver creates new glucose from proteins in a process called “gluconeogenesis”. This is translated as “making new glucose”.
  4. Ketosis – After 2 to 3 days into the fast, lipolysis starts, which is the breakdown of fat for energy. Fat, known as triglycerides, is broken into the glycerol and three fatty acid chains. Glycerol is used for gluconeogenesis and the fatty acids directly for energy.
  5. Protein conservation phase – After 5 days of fasting the high levels of growth hormone will maintain muscle mass and lean tissues. The energy for maintenance of basal metabolism is almost entirely met by the use of free fatty acids and ketones.

Many people are aftraid that they will lose their muscle while fasting but this is not the case. During this period, excess proteins are indeed broken down for glucose. But this is not necessarily muscle. There are connective tissue, skin, old cells and other junky cell parts that can be destroyed. This is the magic process of autophagy!

The body will then proceed into rebuilding any necessary proteins that were used up. This completes the cellular renewal cycle. It’s like cleaning your closet. You can’t simply put more clothes if the closet is full. You first need to remove to the old ones. Breakdown of old protein is necessary for renewal of cells.

Hormone regulation

  1. Insulin – Blood glucose levels remain normal, as the body begins to switch over to burning fat for energy. Regular fasting, in addition to lowering insulin levels, improves insulin sensitivity. This is the key in the weight-loss puzzle. Most diets reduce calories and do not address the insulin resistance issue. Eating frequently keeps the body insulin resistance As already discussed intermittent fasting is an efficient method of fixing this.
  2. Growth Hormone – Human growth hormone is key for so many functions. It gets released during fasting periods (e.g during sleep) and can increase up to 400% after a 1-2 day fast! It helps to preserve muscle mass and bone density and is a key anti-aging hormone
  3. Metabolism – Although one could expect that once in a fasted state, the body will start slowing down and will reduce the metabolism to prevent weight loss actually the exact opposite happens. The metabolism boost is up-to 4%, which is the effect we want!

What to expect?

Everyone is different and in different adaptation phases, but having done already a few fasts I can say that most if not all people would benefit from a couple of days of fasting once or twice a year. However it is not easy. It can be a challenge mainly for the mind, and for this reason I believe once done you will feel stronger and more disciplined.

Ketones after 26-hours fasting
Glucose after 26-hours fasting
  • Hunger will probably be an issue if you if you are not keto adapted. However, being in ketosis already before the fast will allow your body to tap into fat for energy effortlessly. Of-course meal timing is a very strong habit triggered by hormones (e.g Grehlin), so expect the first day your body to remind you to eat! But this signalling will go away after an hour.
  • Water retention – Expect your body to get rid of excess salt and water. Insulin causes salt and water retention in the kidney. Especially if you a beginner with fasting expect less bloating, and feeling ‘lighter’.
  • Energy – Expect to be full of energy, and focused like a lion hunting down it’s prey. Ketones are the preferred energy of the body and not burdening your body with having to digest food will take your energy to the next level. From an evolutionary perspective this makes totally sense. If you are hungry you need to be alert and at your best to ensure you can hunt.
  • Body temperature – Eating can raise the body temperature up-to 2 degrees Celcius. When not diverting energy into digestion the body temperature will drop and will also help you sleep better and deeper.
  • Weight loss – Expect some serious weight loss! I lost around 2kilos in 2 days.

There are many more areas that fasting will help such as inflammation, auto-immune issues but we will discuss these separetely.

How to best implement a 2-3 day fast

  • Prepare yourself by doing a low-carb diet for a week and intermittent fast.
  • Drink a couple of black of espressos during the day or when you feel hungry. Coffee is a hunger suppressor so it will definetely help.
  • If you feel a bit weak, drink some sparkling water and add some salt and lemon. Sparkling water has some essential electrolytes (magnesium, calcium) while salt and lemon have sodium and potassium which are key for hydration and energy.
  • Take it easy and sleep plenty. Fasting is stressor so you dont want to go over the top
  • When breaking your fast start with a soup or a broth and after an hour eat something light. Even after a couple of days of fasting your body might be sensitive to spices or a heavy meal.

Key Takeaway

  • Fasting is key for health and longevity and should be incoporated periodically into everyones life!

Further reading


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