Intermittent fasting

Intermittent fasting (IF) has become extremely popular lately. But is it really healthy to go several hours a day without eating? Are there any benefits or is it actually harmful? And what types of IF are there?

What is IF?

Intermittent fasting is a diet plan based on eating only over a specific, time-restricted part of the day (eating window) while fasting for the rest of the day (fasting window).

Intermittent fasting is not about any modifications of the intake of calories or macronutrients. It is based on the very same calorie intake, only all the calories and macronutrients need to be eaten over a specific time. The only change when switching to IF is shortening the part of the day during which you can eat and creating a systematic time window for fasting.

When fasting, you need to drink enough water, unsweetened tea (ideally black and green) or black coffee. However, you should avoid anything which contains calories and could be a strain to your digestive tract (i.e. interrupts fasting and starts digestion). Also, avoid bubble gum, candy, flavoured beverages, sweetened tea and coffee with milk.

History of Intermittent Fasting

If you stop to think about intermittent fasting, you’ll realize that fasting used to be absolutely natural. Our ancestors never ate over the whole day every two hours like we do today. A group of cavemen spent several hours hunting and made a lot of effort to kill, process and eat a mammoth. If their hunt wasn’t successful, they had to fast or eat roots or fruits. They would hunt and gather only once in a while.

Today, unfortunately, people sit in front of a television, then take five steps to hunt for something in the fridge, grab a piece of well-processed ham, and five minutes later return for some cheese and a sausage because everything is comfortably within reach.

Wherever you go you are told to eat every three hours, eat most of your calories before lunch and avoid feeling hungry. That’s why lots of people force themselves to have breakfast even when they are not hungry in the morning, quickly grab a granola bar full of fast-acting sugars at work just because they hear that it’s necessary to snack and three meals a day are not enough, and have a salad with some salad for dinner because you should give your dinner to your enemy, as the calories consumed in the evening immediately get stored as fat. How much does this diet match the one people used to follow hundreds of years ago?

Types of IF

The various types of IF are based on the duration of the fasting.

The most well-known type, as well as an option for tough guys, is called the Warrior Diet. Here, people fast for 20 hours and have only a four-hour eating window.

Other common types:
18-hour fasting / 6-hour eating window
16-hour fasting / 8-hour eating window
14-hour fasting / 10-hour eating window
12-hour fasting / 12-hour eating window

Taking a look at the last type (12/12), we can see it’s what some people stick to without even calling it intermittent fasting. They have breakfast at 8 am and dinner before 8 pm.
Today, however, lots of people eat over a period longer than 12 hours, due to stressful lives, too much work, etc. They have breakfast as early as 5 am and dinner as late as 10 pm.
Our digestive tract then has no time to rest, as it’s continuously being given food to process, which may cause a lot of problems (not only digestive).


Experts claim that IF has various benefits. As usual, however, each study shows different results. In general, these are the most frequent ones:

  • Increased insulin sensitivity and decreased insulin resistance
  • Stabilized level of ghrelin (hunger hormone)
  • Higher level of growth hormone
  • Lower level of cortisol
  • Burning fat with no calorie restriction while maintaining muscle mass
  • Positively supported brain activity
  • Improved sports performance
  • Faster regeneration
  • Lower fatigue, more energy during the day, better sleep
  • Saved time (previously spent eating and preparing meals or thinking about what to eat)

I’d Like to Try It. How Do I Begin?

Measure the duration of your current fasting window, e.g. you have breakfast at 7 am and dinner at 9 pm? Your current fasting window is 10 hours.

Prolong your fasting. Start with prolonging your fasting window by two hours. For some people it’s better to have dinner earlier to start fasting earlier, but most people find it easier to have breakfast later. Gradually work your way towards a 16-hour fasting window. Don’t take any huge steps; prolong the window only when you’re comfortable with your current one and have no problems sticking to it.

Be consistent and regular. If possible, start and end the fasting window at the same time every day, e.g. always have breakfast at 10 am and dinner at 6 pm. If there’s a delay of several minutes or you can’t stick to your regime for some reason (party, business trip, vacation, etc.), it’s ok; just remember that your regime will be a bit disrupted for the next few days.

Don’t be afraid to feel hungry. Yes, you’ll be hungry at the beginning. It’s important to keep going for the first several days to let your body get used to the new regime. Drink a lot, have a cup of coffee, clench your teeth, and don’t give up. It’ll get better in a few days.

Make no restrictions in terms of calories. Leave cutting down on calories or macronutrients for when you’re fully used to IF. Cut down on calories one month after setting a new time schedule for your fasting, at the earliest.

Is IF Suitable for Women?

Of course. Unlike for men, there are several recommendations worth reading for women, though.

Women should remember much more than men that they should start to fast very slowly and gradually. The fasting window should be prolonged by a single hour per week, so that the body has some time to adapt. It’s because women are naturally more sensitive to changes and starting too quickly could be exceptionally difficult and discouraging.

Also, because of the menstrual cycle, women may need to consume more energy and calories and may be hungrier at certain periods during the month (mainly during the secretory and menstrual phases). The fasting window thus needs to be shortened. This is why it’s good to listen to your body and adjust the fasting window as needed around the time of menstruation.


Just like any other diet, the IF has its pros and cons and isn’t suitable for everyone. Some will discover it’s a true treasure, while others won’t like it at all. However, if time management is your everyday problem, as you start working early in the morning or it’s a problem for you to have breakfast, give IF a chance. Who knows, you may be pleasantly surprised.


Autorka: Andrea Skolková (@zezivotaandie)