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An Explanation of Fasting and its Effects on the Body

Updated on January 31, 2016

Fasting is practiced by religious people around the globe. Recent studies show that fasting is actually good for your health by exposing cells to mild stress, improving hormone composition and reducing bodyfat, while giving your digestive system a healthy break. There are people who swear on fasting to lose body fat and improve general health. But what actually happens inside your body during a fast?

Body fat and Glycogen

During the fast you lose a lot of water, even if you drink during the fast, you can lose more than a liter of water per day. This is caused by the metabolism of glycogen. When the body is deprived of food it will burn its own energy stores. The body has 3 main energy stores: Adipose tissue (body fat), glycogen (stored carbohydrates) and amino acids (muscle tissue). The first energy store your body will burn is glycogen. Glycogen is a carbohydrate that is stored in the liver and in small amounts in the muscles. When your body burns 1 gram of glycogen for energy, it also uses 2,8 grams of water. Because of this you will rapidly lose (water)weight when fasting. While the glycogen storage is gradually depleting, the body will burn relatively more body fat. When the glycogen stores are depleted, the body will run entirely on body fat. The body will also use some amino acids during the entire fast. 2-3 grams of amino acids will provide the body with 1 gram of glucose. because this is not very efficient the body will try to save amino acids as much as possible. Resistance training has been shown to reduce the use of amino acids significantly.


When the body is completely reliant on body fat as an energy store, which happens when all the stores of glycogen are depleted(48-72h), it will gradually shift from lipolysis(glucose) to ketosis(ketones). From a metabolic perspective this is more efficient. Your body will now use ketones as an energy source instead of glucose. The brain still needs glucose to function properly however. The glucose that the brain needs will be made from amino acids.

Growth Hormone spike

During a 24-hour fast, HGH levels increased an average of 1300 percent in women, and nearly 2000 percent in men. When HGH levels are this high it means the body will try to save muscle tissue. The preferred source of energy will be fats and carbohydrates. As you can see on the picture, your body will secrete more and more HGH the longer you fast and the amount of free fatty acids that are available increase significantly. This shows that the body wants to keep as much lean tissue as possible while burning adipose tissue for energy.

Health benefits

Fasting has been linked to:

  • Increased Growth hormone levels
  • Improved insulin sensitivity
  • Reduced blood pressure
  • Increased HDL (good cholestorol) levels
  • Reduced body fat levels
  • Increased longevity

Do you fast?

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My personal experience

I fast every week on sunday which i have been doing for about 2 months now. For 24 hours i eat nothing. I only drink water and green tea. I usually feel my stomach growling throughout the mornings, but the hunger slowly subsides after a period of time.

It is recommended that you have something to do, so you wont be thinking about food all the time. Thinking about food usually makes me hungry. It is also hard to decline food that is offered to you. People will usually tell you that you are crazy while they eat their french fries and pizza. Actually, most people think you will drop dead if you don't eat for some time.

The breakfast on the next day usually tastes amazing, and it doesn't even matter what it is! Fasting really resets your taste. Food tastes at least twice as good after a day of fasting. I believe fasting once a week is great for fat loss and health. I usually feel more energetic after a day of fasting. I highly recommend fasting one day of the week, especially if other methods don't work for you.

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    • profile image


      4 years ago

      Under the subheading 'Ketosis' it should read "glycolysis" not "lipolysis"

    • CWanamaker profile image


      4 years ago from Arizona

      Awesome Hub. I was planning on writing one about fasting until I read this - Looks like you beat me to it haha. Informative and well researched.

    • andrewreasoner profile image

      Andrew Reasoner 

      4 years ago from Ewing, NJ

      I have been fasting for 18 to 24 hours twice a week for a few months now and I feel great. I even have more energy during my workouts while I fast.

    • profile image


      5 years ago

      Fasting 24 hrs 3 days in a row.surprised how easy its been.hope to weigh in on sat.hope to see at least two pound s.stop for wkend.start again on Mon.

    • Boefie profile imageAUTHOR


      5 years ago from Germany

      wow, going 6 days without food has to be incredibly hard!

    • profile image


      5 years ago

      I am on my 6 th day of water fasting

    • discopig profile image


      5 years ago from USA

      Great article.

    • RachaelLefler profile image

      Rachael Lefler 

      5 years ago from Illinois

      Interesting. I think it's cool that I came across this. What I'm trying right now is a daily fast where no food is eaten during daylight hours (and almost all food would be consumed during just one meal taken at sundown). Do you know how effective this might be as a dieting strategy?

    • profile image


      6 years ago

      The article is more informative and good


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