How can you improve your health and well-being with intermittent fasting? (Click here for the article in English: “Intermittent Fasting”). There is a lot of talk about intermittent fasting, including to lose weight and improve health. Many studies show that it has a great effect on our body and brain and that it can extend life. But what exactly is intermittent fasting and how does it work? The topic of intermittent fasting is popular and controversial.

This article is based on recent studies on intermittent fasting. It was written by Sonja Vlaar and Jocelyn Vlaar for educational purposes; it does not provide advice from a doctor-patient relationship. If you have specific questions or concerns, we recommend that you consult a physician or health professional who can confirm that you are medically healthy to practice intermittent fasting.

Below we explain:

  • What it is, when not to do it, and how to do it
  • How it affects your cell metabolism and hormonal balance
  • The advantages, recommendations and the disadvantages.

What is Intermittent Fasting?

Intermittent fasting is an eating pattern in which periods of eating and fasting alternate regularly. So it's more about when and how you eat, and not so much about what you eat.

Fasting was common until several centuries ago. Our ancestors sometimes had to fast for days until they shot an animal and then there was food again. Our brain-body system is still adapted to function without food for a longer period of time. In fact, it is more natural to fast than always consuming 3 or 4 (or even more) meals a day.

Moreover, in many countries, fasting is a religious or spiritual ritual. For example, Ramadan prescribes periods of fasting for Muslims.

When NOT to do intermittent fasting

It is better to CANNOT intermittent fasting if you:

  • Pregnant – you desperately need the extra nutrients for yourself and your baby.
  • Wanting to get pregnant – it can negatively affect fertility.
  • Breastfeeding – you need extra nutrients for your baby.
  • Suffer from chronic stress – a small-scale study in women shows that fasting for 72 hours increases the stress hormone cortisol. In chronic stress, the cortisol level is already elevated. (15).
  • Under 18 – you are growing and need extra nutrients to grow.
  • Are underweight (BMI < 18,5) or have an eating disorder such as anorexia.
  • have diabetes; then intermittent fasting can be harmful to you.
  • Taking blood sugar-lowering drugs – you run the risk of hypoglycemia due to low blood glucose levels.
  • Already have low blood sugar or marked blood sugar swings – for the same reason as above.

How do you do it?

You can try whether intermittent fasting is for you.

There are several ways and maybe there is one that suits you:

  • Skipping a meal now and then: Skipping breakfast, lunch, or dinner.
  • The 16/8 method: You only eat for an 8-hour period. For example, you allow yourself to eat from noon to 12.00 p.m. This creates a fasting period of 20.00 hours. Not eating for 16 hours means you're not using anything that contains calories, including milk in your coffee or honey in your tea.
  • 24-hour fasting: This involves eating nothing at all from one time on one day to the next day at the same time, one or two days a week. On the other days you eat normally.
  • One meal a day: Also called “OMAD” or “one meal a day”. This is a daily fast day. During the day you drink herbal tea and/or water, but you should not have milk or creamer in your coffee.
  • Every other day: In this method, you alternate a day of fasting with a day of normal eating. A variant of this is that you do calorie restriction on the day of fasting. You do eat, but you limit it to 500 calories or 1/4 of what you normally eat in calories.
  • Long fasting: for 5 days you eat a reduced calorie intake of 500-600 calories per day and the rest of the month you follow the 16/8 method.


  • 5:2 method: Although some call it intermittent fasting, I don't really consider this a form of intermittent fasting. 5 days a week you eat normally and the other 2 days you eat very little (women 500 kilocalories and men 600 kilocalories per day). The 2 days do not have to be consecutive, so you could do that on Wednesday and Sunday for example.

How Intermittent Fasting Affects Your Body

Eating less occasionally gives your digestive organs some rest and also provides health benefits.

When you fast, everything in your body changes on a cellular and hormonal level. Your body releases hormones that make stored body fat more available to meet energy needs. Important repair processes are also set in motion and the expression of your genes changes.

The following changes take place in your body when you fast:

  • The Human Growth Hormone (HGH): The values ​​of these can be up to 5 times higher than when you are not fasting. HGH promotes the loss of body fat and an increase in muscle mass. (1)
  • Insulin: The insulin sensitivity of your body cells improves, causing a significant drop in insulin levels in the blood. Lower insulin levels make stored body fat more available as an energy source. (2)
  • Cell repair: Fasting initiates all kinds of cellular processes, which ensure that the cells can handle stress better and disease processes are prevented. The cells also start a repair process. The cells eat old and defective parts that accumulate in the cell. This is called autophagy. (3, 4)
  • gene expression: Research shows changes in the function of several genes involved in longevity and protection against disease. (5).

These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.

Benefits for your health

An increasing number of studies, in both animals and humans, show the many health benefits of intermittent fasting. It is powerful for weight management and for the health of your body and brain. Even the service life can be extended. (6)

An overview of the benefits:

  • Weight loss: Intermittent fasting can help you lose weight and belly fat, if at the same time your calorie intake is lower (18). Because you eat less often, you often get fewer calories. But if you eat more per meal during your eating periods, there is a good chance that you will not lose weight. Especially if you stuff yourself with unhealthy food. You get the best effect with a Mediterranean diet.
  • Insulin resistance: Intermittent fasting can reduce insulin resistance, dropping insulin levels by up to 30% and blood sugar by up to 6%. This protects against type 2 diabetes.6)
  • Inflammation: Some studies show a reduction in markers of inflammation, the leading cause of chronic disease. (7)
  • Heart health: Intermittent fasting can lower “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance — all risk factors for cardiovascular disease. (3, 8)
  • Cancer: Animal Studies Suggest Intermittent Fasting May Prevent Cancer. (9, 10).
  • Brain health: Intermittent fasting increases the brain hormone BDNF and may promote the growth of new nerve cells. It increases synaptic adaptation, promotes neuron growth, improves overall cognitive function and reduces the risk of neurodegenerative diseases. It could also protect against Alzheimer's and Parkinson's disease. (3,11, 12, 16).
  • Anti-aging: Intermittent fasting can extend the life span of rats. Research in humans is still limited. (13)
  • Long term memory: A study in mice shows that intermittent fasting in the form of eating every other day is more effective than daily calorie restriction in improving long-term memory performance. (17)
  • Lifespan: The same study in mice provides evidence that this improvement is associated with increased neurogenesis of adult neurons in the hippocampus and expression of the longevity gene Klotho. (17)


To take advantage of the health effects of intermittent fasting, it is important that you do not eat for at least 12 hours in a row. Because you do both calorie restriction and intermittent fasting and eat differently for a longer period of time, the health effects are much greater. Only then do the glycogen stores (the form in which glucose is stored in the cells) run out in the body's cells. The body then switches to using the body's fat stores and produces ketones (the end product of fat breakdown) which it uses as fuel. According to episode 8 of the documentary series PROVEN About healing breakthroughs backed by scientific research, prolonged fasting gives you an energetic feeling, you don't feel hunger and you can think better once the body has switched from using glycogen to ketones.

After about 12 hours, the glycogen stores – the form of stored energy from carbohydrates/sugars in your body cells – are empty, after which your body starts burning fat and producing ketones. Depending on your lifestyle, your glycogen stores may run out a little later or sooner. It is better if you can stretch it for a few more hours to about 16 hours or more so that you burn fat for a few hours. For example, if you don't eat after 20.00 p.m., you'll have fasted for 16 hours if you eat lunch at noon the next day.

If you are fasting for a longer period of time, it is important not to eat or drink any carbohydrates at all. Also be careful with carbohydrate-rich fruits and vegetables, such as boiled carrots or bananas. This turns on your metabolism: your blood glucose rises, causing your body to produce insulin.

Proteins also trigger a metabolic reaction. The body converts proteins into glucose (also called gluconeogenesis), which produces insulin (14).

And if your body makes insulin, it can't burn fat at the same time. Insulin allows for the storage of sugar in the cell, while the idea of ​​fasting is correct to rid the cells of stored sugar. The consequence of eating carbohydrates and proteins is that you break the fast cycle, so that the effect is much less.

What you can eat, up to a maximum of 500-600 kilocalories, are fruits and raw vegetables with few carbohydrates and fat, such as coconut fat. Coconut fat is a very good source of energy, it has no influence on your blood sugar level and therefore on the production of insulin.

And it is very important to drink plenty of fluids while fasting, such as plenty of water, green tea or black coffee. Caffeine stimulates your metabolism, so it's great to start the day with.

Also, don't use sweeteners. Although they contain no calories, it is unclear what the effect is on insulin production.


Intermittent fasting has many benefits. However, you can also experience less pleasant side effects:

  • hunger is the most common side effect of intermittent fasting. This usually comes in waves and goes away on its own. By drinking a lot you can at least suppress the feeling of hunger better. And it also helps with a rumbling stomach.
  • Constipation occurs regularly, also because you eat less. But if you suddenly eat a lot more fiber than usual, constipation or constipation can result. You can use some Epsom salt (from the drugstore or pharmacy) and take it with a glass of water before going to bed.
  • Headache. It can also prevent you from getting a headache. This usually passes after the first few days of fasting. Taking some extra salt can often help reduce the complaint.
  • You can use dizziness and heartburn to get. In case of dizziness, it helps to drink and take in enough salt. Eating a large meal too soon after fasting can cause heartburn symptoms. Eat slowly and calmly and do not lie down immediately after eating.

Why this article?

Science is constantly evolving and there are many new insights about nutrition. We cannot possibly keep up with all of these developments. Why are we writing this article right now?

When I (Sonja Vlaar) graduated from Wageningen University in 1983 in Human Nutrition and Health, I had never heard of Intermittent Fasting. I learned about it in the spring of 2020, when I took the Neurozone® Enhanced Course for Coaches. In my personal Neurozone® assessment in 2020, intermittent fasting was mentioned as one of the recommendations for promoting my resilience and high performance. That made me so curious that I wanted to know exactly what intermittent fasting is all about. That's how I started this article.

The COVID lockdown has stimulated many people to take a closer look at the well-being rhythms of their own brain-body system. In previous articles I shared my insights about the basic rhythms of exercise and walking, the deep breath and over food and our brain. More than ever we realize how important it is to take good care of these basic rhythms and that we need to adjust our mindset about the functioning of our brain-body systems. The neuro-biological rhythms are the foundations for improving our performance.

Please contact Sonja Vlaar ( or Jocelyn Vlaar ( for more information.