Intermittent Fasting – check out how it works!

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The IF diet is becoming increasingly popular. It raises a lot of controversy and contradictions between dieters. Her supporters praise her very much, the opponents have hundreds of arguments against its use. I will try to explain what it is and who it can apply to.


  1. IF diet – what is it?
  2. Why should you eat this way?
  3. Who can use IF diet?
  4. Disadvantages of IF
  5. Summary


  1. IF diet – what is it?

Intermittent fasting (abbreviated as IF) is a way of eating, which consists in taking food only for a certain period of time during a day or week, while for the rest of the time we deliberately refrain from eating. There are different versions of the intermittent post. The most popular is 16/8, where we fast for 16 hours, and meals are eaten in an 8-hour nutritional window. In practice, this means that in the morning we leave breakfast, the first meal we eat only at noon, and the last one at the latest at 20.00. The duration of the nutritional window should be adjusted individually so that it can accommodate the amount of food that will satisfy our need for energy and nutrients. Those who approach this issue more rigorously shorten window time, e.g. up to 4 hours.

Another method called 5/2 is a substantial caloric restriction for 2 consecutive days a week, and for the remaining 5 days we use our usual diet. It should be noted that whatever kind of fasting we choose, the quality of the products we eat is also important. They should be low-processed, full of vitamins and minerals. You should avoid fast food, sugar, shop snacks, alcohol, etc. When you avoid meals, you can not forget about proper hydration. In addition to mineral water in smaller amounts, you can drink unsweetened black coffee or tea. It is also acceptable to chew sugarless chewing gum.

  1. Why should you eat this way?

Fasting is something natural for mammals. The human body is perfectly adapted to the difficult access of food. During fasting, when the glucose stores in the body are exhausted, alternative energy recovery routes are activated. In the liver, so-called ketone bodies, which are the fuel for body cells. This is due to the activation of glucagon, or antagonistic hormone to insulin. Insulin, in turn, is mainly responsible for increasing body weight, both muscle and fat.

In people with low physical activity, excess insulin results in the accumulation of unnecessary kilograms in adipose tissue. By reducing the amount of secreted resting insulin, the sensitivity of cells to this hormone is increased, fasting blood glucose is improved and release of stored fat stores is also possible. Intermittent fasting is therefore a very helpful tool in the prevention of diabetes and in the fight against insulin resistance.

Many people are afraid that reducing the amount of meals will result in the opposite effect, that is, slowing down metabolism and weight gain. That’s wrong! However, studies have shown that the metabolic rate is identical, no matter how we divide the amount of calories consumed during the day. Short-term fasting (lasting up to 48 hours) may even increase resting metabolism from 3.6% to 14% due to a higher level of noradrenaline in the blood. However, above this time the effect will be reversed, therefore the periodic post is a better solution. Apart from energy balance, other aspects are also important, first of all to what extent nutrients are absorbed in our intestines. It is related to, among others with the condition of the intestinal microflora. IF helps in weight reduction also by regulating the hormones responsible for the feeling of hunger and satiety – ghrelin and leptin.

Research shows that periodic fasting has a cardioprotective effect. First, it lowers the levels of homocysteine, triglycerides and LDL cholesterol in the blood that contribute to the development of atherosclerosis. Secondly, cyclical fasting helps reduce blood pressure, reduces oxidative stress in cells and markers of inflammation – interleukin 6 (IL-6), CRP and TNF-alpha.

Another advantage of intermittent fasting is better regeneration of the body. Autophagy processes, i.e. destruction of old used cells, are intensifying. Many people using this system improve the functioning of the brain, there is a better quality of sleep, memory, concentration and general energy level. What’s more, studies on both animals and humans show that periodic fasting can act anti-cancer and prolong life by activating sirtuins, or longevity genes.

  1. Who can use IF diet?

Periodic fasting may be a good solution for people with glucose and insulin disorders as well as obesity. By  suppressing appetite, slimming is much easier. In addition, it can contribute to the improvement of health in people at high risk of atherosclerosis, diabetes and heart disease, and inflammation.

People using a ketogenic diet at the same time can quickly get the appropriate level of ketone bodies in the blood thanks to fasting. Shift workers will also benefit greatly as IF helps regulate the circadian rhythm. An additional advantage of reducing the amount of food is to save time. You do not need to make several meals a day, which is important especially for those who travel frequently.

  1. Disadvantages of IF

Periodic fasting is not an ideal diet for everyone!. For some it is very difficult to endure many hours without food, especially at the beginning. Dizziness and fatigue may occur during the adaptation period. Before the brain starts to use ketones effectively, it will demand “glucose” in the form of glucose, making it easier to indulge in sweets and other snacks. There is also a greater risk that you will be tempted to compensate for your hunger strike. This may result in excess calories and not very healthy dishes. IF is also not recommended for patients with reactive hypoglycemia. Such people should increase the frequency of food intake throughout the day to prevent the blood sugar level from falling too drastically.

Skipping meals may disturb the production of digestive enzymes. If for most of the day the digestive system is “dormant” and then forced to process a large portion of food, digestive problems may arise. This is not the rule, because some (for example those suffering from gastro-oesophageal reflux) often have a noticeable improvement. If you are in doubt about your health condition, consult your doctor before starting your diet.

Each body is different, so it’s difficult to predict all reactions to change the way of eating. One of the negative reactions may be increasing the feeling of stress, because our body is at first exposed to several hours of hunger and sometimes to overeating. Therefore, people with dysregulated adrenal glands should approach IF with caution.

Too large caloric restrictions, which often accompany periodic fasts, contribute to the dysregulation of women’s hormones, which leads to the halting of ovulation. Therefore, IF may not be a good idea especially for women with low body fat. It is important that women who use this system do not reduce the time of the nutritional window too much. It is best if it lasts 8 or even 10 hours.

Another problem is the difficulty in covering all-day energy needs and all nutrients in only 1-2 meals a day. An obese patient who is on a reducing diet should remain on a caloric deficit. However, if you are dealing with a person who is doing heavy physical work or intensely training at the gym, the matter looks completely different. Of course, this is not the rule either. Many sportsmen appreciate IF because it facilitates the growth of pure muscle mass while maintaining low body fat levels. What’s more, research has shown that during fasting increases the level of growth hormone (somatotropin) in the blood.

Periodic fasting can be problematic if we have been eating meals with family or friends so far and when our work requires frequent business meetings during lunch. Think about whether we have a strong will to refuse a meal together. In addition, intermittent fasting should not be used by children, pregnant women and people who do heavy physical work.

  1. Summary

Periodic fasting can be a great way to lose unnecessary kilograms, improve well-being, prevent or cure certain diseases. It is particularly well-suited for people with metabolic syndrome. However, like other eating models, it also has its drawbacks. Before we decide on an intermittent post, one should consider what is our mode of work, what is our daily physical activity looks like and what goals we want to achieve. The diet should always be selected individually for our needs and state of health, so that it can bring as many benefits as possible.


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