How long should you fast? That depends on which health benefits you’re trying to tap into. The longer you do fast however, the more the health benefits begin to add up.
This does not mean that long fasts are for everybody. It depends. As an example, if you’re just trying to increase ketone levels for sustained energy and improved cognitive performance, then a 17 or 18 hour fast (which can be performed daily) might be enough. However, if you’re trying to reduce chronic inflammation or metabolic disorder then stretching it out to about 72 hours could stimulate the appropriate physiological response.
Here are the benefits of fasting broken down by the number of hours fasted:
13-16 hour fast
A 13-16 hour fast is considered to be intermittent fasting and can be conducted daily. At 13 hours of fasting, the digestive system down regulates (goes to sleep) and your body will begin to secrete more human growth hormone (HGH). The HGH assists in a variety of processes including the maintenance of lean mass, burning fat and slowing down the ageing process.
At this point, the body is transitioning to the use of stored body fat for immediate energy.
16 hour fast
This is when most people begin to produce additional ketones. Ketones are a sign that the liver has transitioned from burning glucose (sugar) to burning fats for energy. In addition, ketones are neuro-protective and will move into the brain, giving you energy and a greater mental clarity.
Also, HGH production continues to increase and the body begins to accelerate the fat burning process.
18-24 hour fast
At 18 hours, the body will begin to stimulate autophagy. What this means is your cells internal intelligence has been switched on and they are able to repair themselves by cleaning out old and / or damaged cells.
At 24 hours, your intestinal cells reboot and GABA production increases. GABA is the neurotransmitter known to relax the brain and help with anxiety.
At this point in time, the body would have depleted its liver glycogen stores and would now be operating primarily on ketones (from the break down of fatty acids) for energy.
36 hour fast
The longer you fast, the more it forces your body to deplete glycogen stores, and release stored energy in the form of body fat (an evolutionary adaption in response to not having a constant food source). As the body breaks down stored body fat and converts it to usable energy, the body also releases toxins that have also been stored within the fat cells. Proper hydration and even supplementation with a binder, such as charcoal may help the body to eliminate toxins during periods of fasting.
36-48 hour fasts is where to start to see an increase in stem cell regeneration, fat loss, greater anti-ageing benefits, and an increase in dopamine levels.
At this point, autophagy increases by approx. 300%.
48 hour fast
At 48 hours, cellular regeneration commences and inflammation begins to decrease. Autophagy continues to increase and the body begins to reset dopamine receptor sites.
72 hour fast
This is where autophagy peaks.
+ 72 hour fasting
Although longer fasts can be beneficial, fasting for periods greater than 72 hours should only be conducted under medical supervision or with consultation.