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Shocking simulation shows exactly what happens to your body when you fast for 72 hours

Home> News> Health

Published 13:46 4 Jun 2025 GMT+1

Shocking simulation shows exactly what happens to your body when you fast for 72 hours

Abstaining from food for 72 hours has a surprising impact on a person

Niamh Shackleton

Niamh Shackleton

Featured Image Credit: YouTube/5MinRaw

Topics: Health, YouTube, Food and Drink

Niamh Shackleton
Niamh Shackleton

Niamh Shackleton is an experienced journalist for UNILAD, specialising in topics including mental health and showbiz, as well as anything Henry Cavill and cat related. She has previously worked for OK! Magazine, Caters and Kennedy.

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@niamhshackleton

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A simulation has shown the process your body goes through when you fast for 72 hours.

There are both pros and cons to fasting, and the negatives of it probably won't come as a surprise to you.

Without fuelling your body with food, you might experience things like fatigue and low energy; hunger pains; dizziness; dehydration; and bad breath - and that's just a handful of how you might feel while fasting.

While fasting isn't for the faint of heart, there are some health benefits to it.

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A simulation shared to YouTube broke down the interesting process of what happens to your body the longer you go without eating.

After eight hours without food, the food already in the digestive tract is consumed for fuel and glucagon is released by the pancreas which triggers the liver to release glucose.

Fasting is growing in popularity for its reported health benefits (Getty Stock Image)
Fasting is growing in popularity for its reported health benefits (Getty Stock Image)

As this happens, ghrelin (an appetite-stimulating hormone) is excreted causing you to want to eat.

When you hit 12 hours of fasting, the human growth hormone (HGH), also known as somatotropin, is released from pituitary gland which is located in the base of the brain. This then stops the breakdown of muscle tissue.

Per the YouTube video, it's at this point that you'll also experience a decrease in body temperature and the body turns to its fat stores for energy.

Next you'll experience autophagy. Cleveland Clinic describes this as 'a natural cleaning out process that begins when your cells are stressed or deprived of nutrients'.

"Autophagy allows your body to break down and reuse old cell parts so your cells can operate more efficiently," it adds.

When you eventually arrive at the 36 hour mark, fat will become the body's main source of energy (mental and physical).

For those of you who struggle with the feeling of being hungry, it's apparently not until 48 hours into a fast that the feeling subsides. With this in mind, your mood and alertness improve.

When - or should I say if - you hit 72 hours of fasting, you can start 'gently resuming eating' as your body resets. It's said that the benefits you experienced during the fast will continue for the days that follow after you begin eating again.

A lot of people swear by fasting, Sharon Osbourne included. Speaking on her podcast back in 2023, the former X Factor judge said that she goes 'at least three days without eating' on a weekly basis.

While there may be some health benefits to fasting, people are urged to seek out medical advice before planning on going long periods without food.

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