Intermittent fasting
Intermittent fasting

How to do intermittent fasting for weight loss?

How to do intermittent fasting for weight loss? Is it efficient or healthy? Does fasting create a yo-yo effect that will place us right where we started once we start eating like before?

In this article we will focus on finding out what the science behind fasting is and what are its health benefits.

What is fasting?

Fasting has been around from the beginning of time, and it became a staple of religious practice, as there are different fasts throughout the year in all religions.

Using fasting as a diet is a different approach that implies not consuming any calories for a number of hours.

The fasting periods range between 12 to 16 hours, and the caloric intake during a day can be very different too.

The purpose is to deplete the body’s glucose reserves, and to stop it from focusing on digestion by giving the digestive system a well deserved break.

How does fasting work?

To understand how fasting works, we need to first learn a bit about how our digestive system works.

We covered this information extensively in this article, but we will summarize it here too.

Our cells need energy in order for us to function properly. We obtain this energy through food.

When we eat, the food is broken down to nutrients with the help of digestive acids and enzymes. Later, the broken down nutrients are absorbed through the small intestine into the bloodstream.

The nutrients that can be transformed in energy are: glucose, proteins and fat. Our cells prefer glucose because it burns fast, and it takes little work to process.

For glucose to enter a cell, it needs insulin. Insulin is produced by the pancreas and the production is based on request.

This means that the pancreas will not produce insulin if we don’t eat anything that is transformed in glucose.

While we fast, the pancreas takes a break and the cells don’t receive any new glucose.

This is important because it changes us in a few very important ways:

  • It helps lower glucose sensitivity – fighting glucose resistance;
  • Diabetes can be prevented or even controlled;
  • The “hunger hormones” can be regulated;
  • We begin to use other resources like fat, to produce energy – thus promoting weight loss.

Fasting vs. Intermittent Fasting

A few centuries ago, when our society wasn’t evolved enough for humans to have access to food all the time, fasting was a way of life.

People ate when they had to and if they had food. The rest of the time was spent outside, working to get food. We were hunters-gatherers and everything we did revolved around obtaining calories and shelter.

Now, we have too much access to food, and we are constantly snacking while sitting.

While fasting for long periods of time (days, or even weeks) can be done, it requires medical supervision, as it can be dangerous.

Even if we want to lose weight, we still need nutrients like vitamins and minerals. So, scientist began to study intermittent fasting.

This type of fast was studied by many researchers and it was found to be effective and most importantly safe.

Health benefits of fasting

It is interesting to note the fact that a few decades ago medicine looked more at how it can offer patients more nutrients and now it finds that too many nutrients are actually bad for us. It turns out that you really can have too much of a good thing.

There are many health benefits that intermittent fasting has to offer. And, surprisingly, they aren’t related only to weight loss. It affects the brain too, and in a very positive way.

Intermittent fasting was found to:

  • Lower blood glucose levels, and on the long term glucose tolerance and Hba1C[i] levels.
  • Be healthy for the heart by preventing many risks for the cardiovascular system like high cholesterol and hypertension[ii].
  • It’s a great option for those who suffer from type 2 diabetes and other metabolic disorders[iii];
  • Weight loss is as efficient as in a typical diet where caloric restriction happens all the time;[iv]
  • It improves memory and cognition. I have to say, that this is one of the most interesting “side-effects” because hunger might have helped us evolve. We needed to become smarter to be able to find more food, and feeling hungry was our motivation;
  • Maybe the most impressive result of fasting is the fact that it can increase lifespan[v].

Furthermore, fasting seems to have an influence on cancer cells. It starves them, because they don’t have adaptation mechanisms like normal cells do.

Intermittent fasting was proven to be efficient in people who undergo chemotherapy, by helping it kill cancer cells, thus improving the outcome of the patients. You can read more on the implications of fasting in cancer treatment and prevention in this study[vi].

Why aren’t more people practicing intermittent fasting?

Most people aren’t aware of these facts, and this is probably why intermittent fasting doesn’t have as many fans as it should. But with the emergence of new information on the subject, and with the intense publicity that it got during the past few years, it is bound to catch-up.

Intermittent fasting is also difficult in the beginning. It takes time for the body to get used to the new conditions, and it tends to protest by exhibiting excessive hunger, fatigue and headaches.

Most people get over the initial symptoms in a maximum of three weeks. Like all habits, once they form, they become the norm and eating habits don’t differ much.

There is also the problem that for generations humans were exposed to some form of starvation. Even when we were children we were told to finish everything from our plate because of our history with lack of food.

This registered in our subconscious mind, and we find it difficult to let it go as we always view hunger as something bad.

How to do intermittent fasting for weight loss?

There are many forms of intermittent fasting.

One of them is the diet 5:2 which can be adapted to become 5:3.

This diet uses a small number of calories for 2 or 3 inconsecutive days a week, and a normal diet during the rest of the week.

During the fasting days of this diet women should eat a maximum of 500 calories and men up to 600 calories. This seems extremely restrictive, and it truly is. But it was shown that it does not have a yo-yo effect and it is very efficient in weight loss.

Furthermore, scientists believed that subjects would eat enough calories during the rest of the week, to compensate for the lost ones. This didn’t happen in clinical trials and a constant weight loss was observed[vii].

Those who find it too difficult to eat such a restricted diet can fast for a number of hours in a day. This approach makes it much easier because 8 of those hours are spent sleeping.

An interval of time between 12 and 18 hours of fasting, in a day, brings all the incredible benefits that we talked about. With an 18 hours fast being the most efficient.

However, animal experiments showed that the best results were achieved when the subjects fasted during a time that was proper for their circadian rhythm. These subjects were the ones that lived longer.

The mechanism through which fasting works well with the circadian rhythm isn’t yet understood. Scientists believe that there is a connection between the free radical neutralization that happens during sleep and the metabolic changes that happen while we eat.

What does this mean?

It means that if you want to try intermittent fasting, it is better to eat late in the morning and at lunch, and to fast in the evening and during the night.

Going to bed on an empty stomach might sound like a punishment, but your stomach will love you for it. And not just your stomach – your pancreas is building you a statue just for thinking about it.

You can read more about the circadian rhythm in one of our sleep related articles. This will help you better understand what goes on when you sleep.

Fasting was a way of life through our evolution as a species. We learned to adapt to it so much that our body now needs it. It is a pause that allows our other important functions to work uninterrupted and we should try to convince our brain that it’s a good idea to skip a meal.


[i] A blood test that reflects the evolution of the blood glucose levels over the past few months. It’s a blood test that diabetics and pre-diabetic people take.

[ii] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7415631/

[iii] https://spectrum.diabetesjournals.org/content/33/2/143

[iv] https://pubmed.ncbi.nlm.nih.gov/26384657/

[v] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7230387/

[vi] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6938162/

[vii] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/

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