For how long should I fast?

Written by Liz Withyman
February 19, 2024

For how long should I fast?

This is a question I am frequently asked and there is no simple answer, because it depends on your objectives.

Different fasts achieve different results

Here is a run down of the principle benefits from different fasting periods.

Length category #1: 16 hours fasting / 8 hours eating ~ the 16:8

This is a common Intermittent Fasting pattern (although some people do 14:10 and see benefits too).

With this pattern you will likely

  • Switch into the fat burning system, so you will start to make ketones
  • Ketones trigger the production of a neurotransmitter called GABA, which has a calming effect, so you’ll feel calm
  • The brain loves ketones so you’ll feel mentally sharp and clear
  • Ketones suppress hunger so you’ll feel less hungry once your body gets used to this pattern
  • Blood glucose levels are steadied, so you won’t get energy slumps
  • Insulin resistance is reduced – great for your metabolic health
  • Triglycerides are reduced – as above
  • Inflammation goes down – as above
  • Growth hormone increases – which keeps you youthful
  • You get some Autophagy, though more if you fast longer

Length category #2: 17- 23 hours fasting / 7 – 1 hour (s) eating ~ 17:7 – 23:1

The next length category of IF is 17 – 23 hours of fasting.

With this pattern, you’ll get all the benefits above….AND…the Autophagy will intensify.

Autophagy is a process whereby a cell destroys its own contents by enclosing them in its membranes, and then recycles them.

Another phrase used to describe the process is ‘cellular spring cleaning’.

See my other blog post on this topic here.

With this pattern you will likely get these benefits:

  • Autophagy intensifies
  • Mitochondria are repaired
  • Senescent cells, which are maladaptive and can trigger the development of cancer and increase age-related diseases, are killed off in a process called apoptosis

It’s the most amazing detox with no supplements!

Length category #3: 24 hours fasting

The next length category is the 24 hour fast, which sounds hard, but it’s just teatime to teatime 😉 …once you’re fat-adapted (ie used to IF) this is easy to do!

With this pattern of fasting you’ll get you’ll get all the benefits above….AND…a gut healing method that beats all the probiotics and enzymes you can buy in terms of its efficacy. (And it’s free):

  • A reboot of intestinal stem cells
  • Repair if you have a ‘leaky gut’
  • Improvements in IBS / SIBO (Small intestine bacterial overgrowth) symptoms
  • A gut environment in which good bacteria can thrive

Length category #4: 36 hour fasting (‘The Rishi Sunak’ for UK readers!)

The next length category is a little tougher in my book because you have to go to bed without food on one day…

With this pattern of fasting (on the basis of 36 hours fasting: 12 hours eating, repeatedly) you’ll get you’ll get all the benefits above….AND… you’ll really ramp up your fat burning:

  • Lose weight more rapidly than with shorter fasts
  • Tackle the belly fat, including the dangerous visceral fat
  • Turn white fat into brown (healthy) fat

In my experience most people will get weight loss from less extended fasts than this, but for some people the belly fat is very stubborn and this can be an excellent therapeutic intervention.

However, caution must be applied and if you have any doubt, please consult your doctor.

Length category #5 & #6: 48 – 72 hour fasts

48 – 72 hour fasting are beyond the scope of my programs, but I know that they are extremely therapeutic and I occasionally do these myself.

Hunger disappears.

Peace and calm descends.

Why?

Because more dopamine receptor sites are produced and open up, so you simply get more dopamine rushes in life.

However, again, caution must be applied and if you have any doubt, please consult your doctor.

With a 72 hour (3 day) fast, you get a full immune system re-set – for more information about this, Dr Valter Longo is your man.

Build up gradually

In my Coached IF program, 7 Habits for a Vibrant Life, I encourage my clients to build up their fasting practice gradually from whatever their starting point is to 16:8, and then beyond if they so wish.

What I do not advise anyone to do is jump in with even a 16:8 pattern without building up to it.

Slow and steady wins the race.

 You wouldn’t attempt a marathon without training!

There will be difficult moments (which is why being part of a group is so helpful, for the accountability and support).

But difficult moments are where your growth lies.

And unlike dieting, which sounds easy (nice, neat meal plans) but in reality is really hard; intermittent fasting sounds hard (whaaaat? No food for hours on end?!) but in reality is easy….and trust me, it gets easier and easier.

Liz Withyman

Liz Withyman is an ICF-registered ACC (Associate Certified Coach) who trained with the Coaches Training Institute, the most rigorous and respected coach training in the industry. She runs her online Coached Intermittent Fasting Program 7 Habits for a Vibrant Life several times a year. 

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