Paracelsus, the famous Renaissance physician and philosopher, already considered fasting to be the greatest of all remedies in his time, without having a research laboratory. So, what clues in this direction does modern science provide us with?

Fasting is used for its dietary and therapeutic benefits. A moderate fasting period would regenerate the body: The liver and intestinal walls regenerate, the pancreas and stomach are rested, the intestinal flora is rebalanced, The immune system does its housework, the blood sugar is controlled, and the skin is purified. It also boosts brain function and prevents neurodegenerative disorders.

The Way We’re Eating Now is Not How Our Bodies Are Intended To Work

The emperor penguin is an expert on fasting. It can last up to five months of the year without eating any fish, surviving on its fat reserves and losing up to half its 33 lbs (15 kg) weight in temperatures of minus 140 degrees Fahrenheit (60° Celsius).

We don’t have much in common with him. We eat almost all the time, except when we sleep. The three daily meals have been so deeply rooted in our consciousness for generations that it is absolutely unthinkable for a majority of people to give them up.

To which we add snacks, soft drinks (often sweetened), and to finish the day, a glass of wine or a beer with a small bag of salty snacks.

The food industry rubs its hands together, while our bodies show despair. “We are an abundance society, food is always available, and at the same time we barely move,” says Dieter Melchart, professor of complementary medicine at the Technical University of Munich, Bavaria.

This leaves behind traces in the form of overweight, diabetes, hypertension, stroke, myocardial infarction, and Alzheimer’s disease.

A look at the emperor penguin, and at the nature to which we belong despite our mobile phones, hot dogs, and over-equipped kitchens, reveals an interesting fact as Melchart points out:

“Life on Earth has developed at the rhythm of days and nights, cold and heat, excess and lack. And we would probably be well advised to accept some deprivation from time to time, and, for once, to go against the continuous engulfment that forms the backdrop of our lives.”

Why Fast: 6 Reasons You Should Clearly Start Fasting

1. Less Food, Less Health Problems

One thing is for sure: excess food damages the body, and even the brain.

The Western-style diet, rich in fatty and industrially processed products, has shown the extent of its damage to our physical and mental health. And everyone who has ever experienced the positive effects of a temporary food restriction on our brain knows about it.

“Once the difficult first three days are over, two-thirds of the patients studied experience a marked improvement in their mood,” reports naturopath Andreas Michalsen of Berlin’s Immanuel Hospital, a place where about 800 patients fast voluntarily each year to improve their health.

2. Our Bodies Are Made For Fasting

From the point of view of evolutionary biology, it seems quite logical that a feeling of well-being should appear after a brief state of hunger.

“If, living in a natural environment, you have not eaten anything for three days and go to bed in your cave, you have every chance of dying,” Michalsen notes.

This is why a fasting adaptation program would have been in place for hundreds of thousands of years in our body. As soon as the supply of food resources becomes scarce, the brain sets in motion a euphoric mode that makes the individual become more active and oriented towards his environment, and does not withdraw into himself, which would be fatal to him. For this reason, fasting acts like an antidepressant.

When fasting, our mood changes in this way:

  1. The body acquires less tryptophan, an amino acid present in our diet that is necessary to synthesize the neurotransmitter serotonin.
    Serotonin improves mood, appetite, digestion, sleep, memory, and sexual desire and function.

  2. The brain also reduces the number of its serotonin carriers in its synapses. These are the molecules that limit the concentration of serotonin in the synapses.

Therefore, as in antidepressant treatment, the effect of which is to reduce the action of these serotonin carriers, the final result is that the concentration, permanence, and effect of serotonin is improved.

3. More Stable Glucose Metabolism

Three star-researchers on the fasting scene confirm the benefits of fasting:

  • According to American cell biologist Valter Longo of the University of Southern California at Los Angeles, fasting slows down aging processes and could have positive effects in the treatment of cancer.

  • Italian gerontologist and biologist Luigi Fontana at the Institute for Public Health at the University of Washington in Saint Louis is examining the effects of voluntary caloric restriction on the cardiovascular system.

  • Finally, for Mark Mattson of the National Institute of Aging in Baltimore, fasting is good for the brain. Both by optimizing the functioning of our neurons and by protecting against neurodegenerative diseases.

Many biologists and doctors share this view. However, the effect of fasting on the different organs of the body has long been studied only in animals.

The laboratories of researchers interested in this theme mainly host yeasts, nematodes, and flies. And of course, mice and rats.

In cages regularly supplied with abundant food, these rodents quickly look like sluggish hangover college students watching TV on their couch.

And as soon as their caloric intake is reduced, beneficial effects are felt: the more they are forced to settle for low rations, the longer they live, and moreover, in better health than their over-fed companions.

Animals that are fasted some of the time actually have a more stable and spread out glucose metabolism; blood markers of inflammation decrease, as do blood pressure and resting pulse.

There are also changes in their brains: neural stem cells produce more nerve cells, especially in a crucial area for memory, the hippocampus. The connections within neural networks are also changing; neurons are making more contact with each other.

Also, laboratory animals do much better in the memory and learning tests they receive.

After fasting, mice neurons genetically modified to be vulnerable to diseases such as epilepsy, Parkinson’s or Alzheimer’s, are becoming more robust.

4. Improved Defence Mechanisms of The Body

According to Michalsen, these animal experiments reveal two main possible mechanisms of fasting action:

  1. Signals that adversely affect the brain and cause nerve cell loss, such as high and persistent levels of insulin or inflammation mediators, tend to decrease.

  2. On the other hand, the lack of food is a stress for the body, which triggers defense mechanisms. For example, cells produce more enzymes that are specialized in protecting against free radicals or in DNA repair, resulting in animals living longer.

In this way, a dietary restriction would increase our ability to resist a little like sport does. This type of effect, in which a priority hostile threat produce beneficial effects, is known as hormesis, a term derived from the Greek meaning stimulation or impulse.

5. Stronger Neuronal Structure in The Brain

At the cellular and molecular level, fasting seems to have a beneficial effect on the brain through four main factors: ketones, BDNF, mitochondria, and autophagy. Which deserves some explanation.

Ketones, such as beta-hydroxybutyric acid produced by the liver and involved in fat breakdown, cross the blood-brain barrier, and serve as an energy source for nerve cells, just like glucose.

A diet rich in ketones produces a decrease in the level of beta-amyloid peptide and tau protein in the laboratory mouse brain, which are characteristic of Alzheimer’s disease according to a research published by Mark Mattson’s team in 2013.Mice become more capable of learning and less anxious.

At the same time, ketones released under fasting conditions stimulate the production of neuronal growth factors such as BDNF (Brain-Derived Growth Factor), which stimulates the growth of neurons and their self-defense mechanisms.

In both humans and animals, the production of this growth factor tends to decline with age, but also in cases of overeating, lack of physical activity, or in people with neurodegenerative diseases such as Parkinson’s or Alzheimer’s disease.

But then, wouldn’t the most obvious solution be to simply administer BDNF to patients in order to protect their neurons from dementia?

No, this would not work. Growth Factor is released according to the activity of each neuron individually, at the cellular level, and has a very targeted action at the level of each synapse.

This very finely regulated system cannot therefore be put into action directly, only indirectly by playing sports for example, eating less, and potentially through regular and varied cognitive stimulation.

6. The Body Becomes More Energy Efficient And Gets Rid of More Waste

Caloric restriction also has a positive effect on cell power plants, the mitochondria. In fasting conditions, they produce their energy more efficiently, and new ones are formed!

In addition, food deprivation accelerates recycling processes in nerve tissue: anything that is not used (e.g., macromolecules or damaged organelles) is digested.

Through this cell cleaning program called autophagy (which earned its discoverer, cell biologist Yoshinori Ohsumi, the 2016 Nobel Prize in Medicine and Physiology), cells get rid of the waste that could constitute a hazardous material for them, and which, once reprocessed, can serve as a raw material for the body.

Very Promising Benefits, But…

Thanks to all these effects, fasting seems to oppose processes that, gradually with aging or rapidly in neurodegenerative diseases such as Alzheimer’s, tend to erode the brain’s performance.

Food seems to influence the structure of the brain and the functioning of neural networks in laboratory animals. But what exactly is the situation in humans? Are the facts observed in mice also valid for Homo sapiens?

As observations in patients with chronic pain, rheumatism, hypertension, or overweight indicate, fasting reduces the symptoms associated with these conditions.

Also, it reduces important risk factors associated with the development of diseases or dementia, such as oxidative stress, markers of inflammation, and insulin concentration.

In 2013, Lucia Kerti and her colleagues at the Charité Hospital in Berlin discovered another clue which follows the same pattern: excessive and persistent blood sugar levels in both men and women alter the structure of the hippocampus, which is so important for memory. Moreover, people high blood sugar score lower on memory tests than people with lower blood sugar.

But there are still limits to the transposition of the molecular effects of fasting from animals to humans. Mice and men are – wait for it – different.

In particular, the production of new nerve cells in the hippocampus declines faster in mice than in humans. It is therefore possible that the positive effects observed in the neurogenesis of animals in a food-restricted situation may not be found to the same extent in human patients.

Another example is ghrelin, a peptide involved in regulating appetite and alternating wakefulness and sleep, which enhances memory and learning abilities in mice. But in 2016, a research team led by Martin Dresler at the Max-Planck Institute of Psychiatry in Munich did not observe similar effects in human volunteers.

“Mark Mattson has demonstrated, through countless experiments, that fasting reduces the onset and development of neurodegenerative diseases in animals,” says Michalsen. “But here we are in the middle of the ford.”

What looks very promising in laboratory mice must now be clearly established through human tests. There is still a lack of controlled studies that have analyzed brain volume, synaptic plasticity, cognitive performance in patients before, during, and after a fasting phase.

But no one is required to wait until the results of such studies are published and lead to prevention strategies before testing them in practice.

The great thing about fasting – but also about any balanced diet or adequate sports activities – is that everyone can participate.

Acctually, How Long Can You Survive Without Eating?

After 24 hours, the glycogen stored in the liver is consumed. Then the brain asks for sugar at all costs and must change the way our metabolism works.

Processes such as gluconeogenesis are initiated. In other words, the body produces glucose from other energy sources. Body fats are broken down to produce fatty acids that most tissues can use to meet their energy needs.

The brain derives its own energy from newly synthesized glucose and also from ketones – produced in the liver from fatty acids. Through this mechanism, a man or woman can survive 30 days or more, depending on their body type, without the provision of solid food.

How To Fast Correctly: Tips For Healthier And Efficient Practice

“Those who fast regularly can more easily manage their eating behavior the rest of the time, and thus, lead a longer and healthier life,” says fasting expert Dieter Melchart from the Technical University of Munich.

One of the most recommended methods of fasting is the following, developed by doctor Hellmut Lützner: Deprive yourself of solid food for a week, allowing only vegetable soups, tea, fruit, and vegetable juices. It is also advisable to be accompanied by experienced specialists.

But fasting does not have to mean a week of vegetable juice. There are several variants of this practice, which can be integrated into everyday life according to each situation and each personal health status.

This means that you can eat normally for five days of the week and fast for two days, as proposed by British food scientist Michelle Harvie from the University of Manchester.

According to current research, regularly offering our bodies long periods without eating seems beneficial to our overall health.

Andreas Michalsen, a naturopathic professor at Berlin’s La Charité Hospital, strives to maintain a daily 16-hour window without food, with an evening meal around 6 pm and a late breakfast the next morning at 10 am.

This gives the intestine time to really rest, insulin levels to drop back down over a long period of time, and neural growth factor (NGF) concentrations to rise.

If you wish to fast, you should talk to your doctor anyway. This practice is not recommended for the elderly, children, pregnant, breastfeeding women, or people with eating disorders.

A Look at Fasting in The World’s Religions

For centuries, large faith communities have associated fasting with religious practice.

Closely linked to contemplation and prayer, the temporary renunciation of food is supposed to broaden consciousness and produce a new understanding of oneself and the universe.

For the believer, he participates in the purification of the soul, in penance, in the rejection of evil, in enlightenment, and even in absolution.

Each religion focuses on a particular aspect. What they have in common is a focus on the central purpose: the search for God.


Judaism has different ritual fasting dates; the main feast of reconciliation and fasting is Yom Kippur. On the tenth day of the seventh month of the Jewish calendar year, the faithful fast as a sign of repentance.

Fasting lasts 25 hours; eating, drinking, working, washing, or having sexual activities is prohibited. Almost all this time is dedicated to participation in religious service.


In the early days of Christianity, two long periods of fasting were practiced: 40 days during Advent before Christmas, starting on November 11 (St. Martin’s Day), and 40 days before Easter.

These were restrictions on the consumption of meat, fish, and eggs. Since then, the Advent fast has fallen into disuse (except in the Orthodox church).

Christians see fasting as a means of abstinence, penance, spiritual elevation, preparation for important decisions or events, and an encounter with God. It must be accompanied by prayers and gifts, or commitment to the poor and needy.


Religious fasting is also one of the five main pillars of Islam, prescribed to Muslims by the Koran.

Fasting during Ramadan (the ninth month in the Islamic calendar) is a sign of devotion to God. From sunrise to sunset, no one should eat, drink, or smoke.

Hinduism and Buddhism

Hinduism and Buddhism do not have a fasting period. But the faithful regularly use it for purification purposes. Some Buddhist monks and nuns do not eat anything from noon until the next day – because it is better to meditate on an empty stomach.

In Summary

We are used to eating several times a day, when we are not snacking.
However, this does not reflect the natural functioning of our body. Our body is rather made to go through periods of fasting, from which all our organs benefit, including our brain.

We should, therefore, allow our bodies some time without food, so it could rebalance and restore some of the natural processes that food abundance came to disrupt.

Even today, the men and women of the primitive tribes, who developed apart from Western civilization for millennia, are not likely to develop large bellies, diabetes or Alzheimer’s disease – and it is the same with the emperor penguin on its Antarctic island.


Jim Miller

Jim spent his twenties trying tounderstand how our primitive minds get in the way of self-growth. He has a lot of interesting ideas about human psychology that he doesn't hesitate to share when opportunity presents itself.

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Related Articles


Jim Miller

Jim spent his twenties trying tounderstand how our primitive minds get in the way of self-growth. He has a lot of interesting ideas about human psychology that he doesn't hesitate to share when opportunity presents itself.

Subscribe to our newsletter

Be the first to receive the latest articles and exclusive offers on our products directly in your inbox

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