Dr Aidin Rawshani

Intermittent fasting and periodic fasting


Intermittent fasting and periodic fasting: effects on weight loss and health

What is periodic fasting and intermittent fasting?

Just over 100 years ago, there was a shortage of food and drink on Earth. Today the situation is the reverse. There is a huge abundance of food and drink (at least in Sweden and other high-income countries). One can undoubtedly say that the supply of food and drink far exceeds human needs. Fasting means abstaining from eating one or more meals.

You can fasten both shorter and longer periods, depending on the purpose of fasting and the conditions for fasting. To refrain from meals means that you refrain from calories and the body can instead use the calories that are stored. The purpose of fasting in most cases is to start burning the energy stored in our fat.

We have fat under the skin (subcutaneous fat) as well as around our organs. When we fasten we also consume the sugar (glucose) stored in the liver and muscles. The human body is adapted to fasting, which allows it to be done without any risk to health (at least in the short term and provided that fasting is not too extreme).

Today, fasting has become popular because many believe there are health-improving effects of fasting. People with overweight, obesity, diabetes type 2 and others are able to fast to lose weight quickly. There is no doubt that one can lose weight quickly by fasting. However, it is difficult to maintain weight loss if you lose weight by fasting (see picture below). People with type 1 diabetes should not fast.

This article is about intermittent fasting and periodic fasting, which involves eating all your calories for a shorter period of the hours of the day. This type of fasting involves fasting for periods and today this has become very popular, even among perfectly healthy individuals.

To fasting leads to changes in metabolism

In the course of evolution, man has adapted to fasting. The body does not take harm by abstaining from meals, at least not if the fasting is short-term or periodic. The body’s biological processes continue even though we are fasting and in order to function, as usual, the body must (in solid) begin to burn energy stored in our fat.

Fat breaks down to extract the energy of the fat. Then you lose weight. The most common reason for fasting is burning fat. Most people fasting to burn fat do it through so-called intermittent fasting, which means fasting in batches.

Why do you lose weight when fasting?

When we eat food, the pancreas (pancreas) releases the hormone insulin. This hormone is necessary for the cells of the body to absorb sugar (glucose) from the blood. When fasting, insulin levels in the blood decrease and this starts processes that lead to the body starting to consume sugar stored in the muscles and in the liver, in addition, the body begins to break down fat so that the energy in the fat can be used as a fuel.

Studies show that people who apply intermittent fasting or caloric restriction usually lose 2.5 to 9.9% of their body weight within a few weeks. Read more about carbohydrates and metabolism.

Recommended reading: Why it is difficult to lose weight, but easy to gain weight.

Are there different ways of fasting?

There are several types of fasting:

  • Intermittent fasting means fasting a maximum of 16 hours.
  • Periodic fasting involves fasting for more than 16 hours.
  • Therapeutic fasting involves fasting for more than 2 days.

Effects of fasting

Fasting can bring several beneficial health effects. There are scientific studies that suggest that fasting can be good in countering the development of cancer; fasting leads to weight loss which is good for those who are overweight or have type 2 diabetes; fasting can improve some functions of the heart and blood vessels; fasting can prevent development of risk factors contributing to cardiovascular disease; fasting can improve physical performance.

The effects of fasting can be enhanced if fasting is combined with physical activity, but most people find it difficult to fasting and exercise, for obvious reasons. However, it should be mentioned that only the effect on weight loss and the improvement of cardiovascular risk factors has been investigated in clinical studies. Other effects may be seen as speculation in anticipation of better scientific evidence.

For whom will fit intermittent fasting?

Periodic fasting works for most people and probably fasting is especially good for people with overweight, metabolic syndrome, type 2 diabetes. People with type 1 diabetes, eating disorders, abnormal vision of their body (dysmorphophobia), fatigue syndrome or stress-related diseases should not fast. Those who play a lot of sports can have difficulty fasting because physical activity increases the need for calories.

How to fasten?

You can fasten between 8 hours and 60 hours, but most fasten less than 48 hours. Periodic fasting is as simple as skipping a meal. For example, you can skip breakfast and eat the first meal at lunch instead. Others prefer to skip lunch instead. Replacing a meal with fruit means a lighter form of fasting.

The 16:8 method involves fasting 16 hours and eating food for 8 hours (so you have 8 hours to eat food and this is called “eating window”). Strength training has a good effect on metabolic disorders if performed during fasting. Combining low-carbohydrate foods (LCHF) or Paleo with periodic fasting can accelerate weight loss. Of course, there are several other variants of periodic fasting in which the person himself determines the “fasting window” (ie, the number of hours you want to fast). In the case of periodic fasting, choose for yourself how long you want to fast.

The 5:2 method is a variant of intermittent fasting that involves eating normally for five days and eating a maximum of 500 kcal for two days.

It is completely okay to repeat fasting daily or a couple of days a week. You can evaluate the effect of periodic fasting only after 4 weeks, allowing the body to adapt to the new conditions. In combination with training, the results are seen earlier. Periodic fasting reduces the concentration of the hunger hormone ghrelin, while the satiety hormone leptin increases; many therefore believe that fasting can actually lead to increased satiety.

Several find it difficult to train and apply periodic or intermittent fasting. Most often the body gets used to the new conditions. Symptoms such as irritation, headache and fatigue cease already after a few days. Fasting leads to the release of cortisol, a stress hormone that, among other things, triggers fat burning but the hormone also makes the body more alert, awake and alert. Probably this has been an evolutionary advantage because an alert and awake individual has better conditions for finding food.

If you combine fasting with exercise, you should end fasting with a workout because you need to eat after the workout. For those who plan to apply periodic fasting, we recommend that you set up a schedule of days that you plan to fast, the number of hours and also the diet that you intend to eat under the “eating window”.

During fasting, no calories should be consumed either in liquid or solid form. Drink water, tea or coffee, but nothing containing calories.

Many who apply intermittent fasting believe that coffee, tea and water are preferable under the “fasting window”. Try to minimize the fat content in the coffee.

Effects of intermittent fasting

Intermittent fasting or calorie restriction (that is, eating fewer calories) has several positive physiological effects. Scientific studies have shown that these diets increase the life expectancy of rodents, monkeys and, possibly, people. The studies show that the sensitivity to the hormone insulin improves (increased insulin sensitivity), sugar levels in the blood decrease, and also the concentrations of insulin decreased in the blood.

Proteins, lipids and DNA have been shown to be in better condition in fasting people, probably because cells are exposed to less oxidative stress. Oxidative stress is called the biochemical process in which reactive oxygen radicals increase, these are dangerous for the body.

How does fasting affect the cardiovascular system?

Studies in rats and mice show that in case of intermittent fasting and caloric restriction the heart’s resting heart rate decreases, low rest heart rate is considered positive in cardiovascular terms. Also, blood pressure decreases, which is positive.

Even in people, it has been seen that the pulse becomes lower by fasting and calorie restriction. The blood vessels of overweight work better if you apply periodic fasting.

It is not proved that metabolism (metabolism) drops during short-term fasting. With longer fasting, as with therapeutic fasting (2 days), metabolism may decrease, which is actually a physiological response to changing conditions. When metabolism drops, you do not lose weight as fast as the body tries to save energy by reducing how fast you burn energy.

Intermittent or periodic fasting does not break down muscle mass. It is also possible to increase muscle mass while fasting, provided you eat right and exercise.

Mice and monkeys treated with calorie restriction or intermittent fasting have better insulin sensitivity, which reduces their risk of diabetes and cardiovascular disease.

High levels of harmful lipids (low-density lipoprotein cholesterol, LDL-C) and low levels of good blood lipids (high-density lipoprotein cholesterol, HDL-C) are associated with an increased risk of death and cardiovascular disease. Intermittent fasting and calorie restriction reduce the concentrations of LDL-C while increasing HDL-C, this is positive.

High blood pressure (hypertension) is a serious risk factor for cardiovascular diseases, especially for stroke and acute myocardial infarction. Animal studies show that intermittent fasting and calorie restriction reduce blood pressure (both excess pressure and suppression decrease). Similar changes have been observed in humans; for example, one study has investigated obese women in which 8 weeks of intermittent fasting resulted in extensive decreases in both systolic and diastolic blood pressure, LDL cholesterol and triglycerides. These positive changes are expected to reduce the risk of cardiovascular diseases.

What does calorie restriction mean?

Intermittent and periodic fasting usually involves eating all your calories for a shorter period of the hours of the day. Intermittent fasting is not quite the same as skipping breakfast because you lack appetite in the morning. Fasting requires more structure and planning. Sporadic fasting is quite simple, but in structured fasting it is more difficult to adapt to the new physiological conditions, to implement training, eat low-carbohydrate foods (LCHF) or Paleo. Although sporadic fasting is not as effective as structured fasting, it is not wrong to skip a meal occasionally.

Intermittent fasting does not mean necessarily eating fewer calories. A person who, on average, eats 2500 kcal per day divided into several meals can instead eat the same amount of calories during his eating window, i.e. 8 hours if you follow the 16:8 diet. But in practice, intermittent fasting means that the person eats less than 2,000 kcal, which is probably the most important explanation for losing weight!

Calorie restriction (calorie restriction) means eating fewer calories per day, which means losing weight.

Which meal is most important? Breakfast, lunch, dinner or snack?

It is usually said that breakfast is the most important meal of the day. The truth is that there is no science behind this. There is no one who can answer which meal is most important. It is rather a tradition and culture that govern this view. You will have to decide which approach suits you best. The important thing is that you manage to implement the diet.

Therapeutic fasting

Therapeutic fasting can be defined slightly differently, but usually, fasting lasts over 2 days and in principle, no carbohydrate intake is allowed. The hypothesis is that the stored sugar in the body’s cells is emptied after 2 days and the body then turns to burn more fat. Therapeutic fasting means a sharp calorie restriction, which is likely to explain why you lose weight quickly.

Caloric restriction compared with intermittent fasting

A study conducted in the USA in 2018, examined whether calorie restriction was better than fasting in terms of body weight, maintenance of weight loss and risk factors for cardiovascular disease. The study included people aged 18 to 64 and lasted for 12 months. The researchers did not find any differences between the two diets. The effects on blood pressure, heart rate (resting heart rate), blood lipids, blood sugar, insulin levels and inflammatory markers (CRP and homocysteine) were similar. After the study period, no difference in weight loss or improvement in cardiovascular risk factors was observed.

How long can you fasten?

  • If you are fasting without reducing your calorie intake, then you can fast for a long time. This only means that you eat for fewer hours of the day.
  • If you fasten and reduce your calorie intake, you will lose fast and a lot of weight. However, this diet can not continue indefinitely because, after some time you consume the body’s stocks of nutrients, minerals, vitamins, proteins, etc., combining fasting with caloric restriction is good for losing weight quickly but after some time you have to eat normally again and then get man struggle to maintain his weight loss.


1. Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. May 2003:1-5.

2. Halberg N, Henriksen M, Söderhamn N, et al. Effect of intermittent fasting and refeeding on insulin action in healthy men. J Appl Physiol. 2005;99(6):2128-2136. doi:10.1152/japplphysiol.00683.2005.

3. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults. JAMA Intern Med. 2017;177(7):930-939. doi:10.1001/jamainternmed.2017.0936.

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