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Fasting for weight loss

A few days “Yom Kipur” was observed. It is a day when Jewish people traditionally fast and refrain from working, driving, and using electronic devices. Almost everyone in Israel respects this day- during Yom Kipur you can take a walk on the high way and not see any car driving.

I’m not Jewish but since I live in Israel and I’m not really an athlete anymore, I decided to join the tradition and didn’t eat or drink for 26 hours. During this period I did nothing but resting and lost over a kilo. It was the first time ever I did something like this, because when I was cutting weight before a competition I never stopped drinking and eating completely. The fast was not that difficult, but I did experience some symptoms of dehydration like a mild headache, having problems to concentrate and having a dry mouth. Fasting is a popular weight loss method, so let’s talk about it.

Where did this kilo go?

I didn’t lose much fat and this kilo came back the next day. What exactly did I lose? We’ll get to this question in a second.

But people do fast to lose weight, right?

Yes. There are actually a few types of fasting diets. Intermittent fasting is a method in which people fast once a week, every second day, or every once in a while, whichever fits them best. It can be a full fast or a consumption of extremely low amounts of calories (typically less than 500 kcal a day). Another popular method is to eat only during a certain daily time window (for example- eat only between 14 – 18 pm). All of these diets allow you to drink as much water as you want, which is not the case in a religious fast.

People who choose to do intermittent fasting and keep this regime for long enough, end up losing weight because they reduce their overall energy balance. One fast will not be enough to see results, but over time there will be fat loss due to a negative energy balance.

Are there other health benefits?

It’s no secret that fasting once in a while can be good for your health and has often a spiritual touch.
There are other health benefits:

  • Lower blood cholesterol
  • Lower blood pressure
  • Increased fat burn especially at the end of the fast
  • Improved control over blood sugar, which can be beneficial against diabetes type 2
  • Reduced fear of hunger

(Still, don’t start a fasting diet without consulting a professional)

Okay. Sounds good. Should I fast?

Not if you’re an athlete. Like I stated in the beginning of the article, I’m not an athlete anymore. I would never do this if I still was.

The biggest share of my weight loss was from dehydration. The rest of the weight loss was mainly due to loss of glycogen. Glycogen is the stored sugar in your muscles and liver. It’s the main energy source during fights and crucial for trainings. The difference between full glycogen stores and empty once can be a change of about 2 kilo on the scale.

The disappearing of glycogen in the muscles during a fast is the main reason why I wouldn’t recommend athletes to fast, especially not when they’re in an intense training period. Glycogen stores won’t fill up again after eating one big meal. Those energy stores are refilled at a rate of about 2-5% per hour so it can take up to 2 days of optimal refeeding to completely recover and rebuild the stores. A professional athlete can push quite a lot into 2 days, for me it meant 2-5 ruined training sessions.

Fasting is a commonly used method for weight cutting, but there are better, less destructive ways. If you do choose to fast in order to make weight, you need to make sure you have enough time to eat properly and correctly and recover your glycogen stores. If there is not enough recovery time, choose for other methods.


More about weight cutting, glycogen and everything else you can find in my book ‘Making Weight & Everything Else’


6 thoughts on “Fasting for weight loss

    1. Depends what kind of level you are. Fasting is not recommended for athletes that train hard on a daily basis, because recovery and training adaptation will be put on the line. However if you’re an athletes that trains 2-3 times a week, fasting is not going to harm your performance if you schedule it right.

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