Fasting has been with us throughout human history. Our prehistoric ancestors had to fast for several day, if not weeks (!), especially during winter when food sources have become scarce. Yet the human race did not die out from a few days without food, because our bodies are perfectly adapted to be able to cope with a few days of fasting.

Over the last few thousand years fasting became more voluntarily. Indeed, it is practiced by all major religions as a process of cleansing, rejuvenating, and self-improvement.

Even for the atheist, fasting is well and truly a cleansing and rejuvenating process for body and mind.

As for metabolic health, the abstinence of calories should be done with plenty of fluid intake.

There are several types of fasting:

• Intermitted fasting = regular cycle between eating and fasting. The most popular version is 8:16 (8 hrs eating window, 16hrs fasting) other schedules can be 6:18, or 4:20
• OMAD = One meal a day, with 23 hrs fasting
• Alternate day fasting = food is consumed every other day, with approximate 36 – 48 hrs of fasting
• 3 day fast = no food for 3 days, just fluids
• 5:2 Fasts = eating normally for 5 days, and fast for 2 days per week
• Spontaneous meal skipping = meals are just skipped, without a structured fasting regime

Once we stop eating, our bodies use up glucose and glycogen (the storage form of glucose) as fuel. Once depleted, our body switches to fat burning for fuel.

This fuel switch can only happen when the nutrient sensors, insulin and mTOR, are low. The low levels signal the body to find internal fuel sources.

During a fast our bodies will maintain proper functioning through the following processes:

Autophagy starts after about 18 hrs of fasting. It is a process triggered by low mTOR levels, by which the body utilises fuel in the form of old dysfunctional cell organelles, or old enzymes and proteins. The body can also utilise the old fragments to build new proteins.

Increased Metabolism occurs after approximately 16 – 20 hrs of fasting; stress hormone levels, like cortisol, adrenaline and noradrenaline, rise to maintain metabolism. The resting energy expenditure during fasting rises by 10-12%, so we are more alert and energised.

Growth Hormones (GH) are produced as a result of low glucose levels and elevated stress hormones. They promote muscle growth, tissue repair, and further boost the metabolism. After 3 days of fasting GH is 300% elevated.

Stem Cell activation occurs after approximately 24 hours of fasting. The body mobilizes stem cells (undifferentiated cells) that can become any cell that the bodies needs. Maximum stem cell mobilization occurs after 3 days of fasting.

Ketone bodies are molecule that are produced from the burning of fat. Ketones are a very clean type of fuel which can be used by every cell, especially the brain. They also suppress hunger, and are highly anti-inflammatory.

Activation of BDNF is triggered by elevated Ketone bodies. BDNF (Brain Derived Neurotropic factor), promotes the survival, maturation, and maintenance of brain and nerve cells. BDNF rises significantly after approximately 24 – 30 hrs of fasting.

So fasting truly is a rejuvenating and cleansing process!

Important: If you have any medical conditions or are on medications please consult with your Low Carb Practitioner or Low Carb dietitian to manage fasting safely. You should not fast longer than 24 hrs if you are pregnant, breast feeding, or a child / teenager.