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Origin and benefits of fasting

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Fasting has emerged as one of the most talked-about topics in nutrition and health. Let’s take a look at what fasting is, what effects it has on our bodies, how to do it, and why it has taken on such prominence as of late.

Fasting is a break in the ingestion of food that allows our bodies to do some overall fine-tuning.

At the end of the page, you can find links to the bibliographic studies supporting the references found throughout this post.

Purification and fasting are natural behaviors common across many species: those of you who have pet cats and dogs have probably noticed the way they stop eating and purge when they have consumed something toxic; most animals stop eating while healing from injuries or wounds; migratory birds stop eating for long periods of time; and bears fast during hibernation.

Human beings do so as well. Humans have adapted to periods of scarcity and naturally, we too fast when we are ill.

Detox diets and fasting have been present throughout human history (16). Data on these practices is available in Babylon, China, India, Greece, Palestine, Persia and Rome. Fasting was practiced and recommended to treat and prevent diseases by the ancient doctors Hippocrates and Galen. It was the practice of great thinkers such as Aristotle, Plato and Socrates, as well as of religious teachers like Moses, Buddha, Jesus Christ and Mohammed.

There are a multitude of examples of fasting being used for the preparation of religious celebrations. Easter, a period of purification of body and soul practiced by Christians during Lent, was inspired by one of the most famous fasts in history: the 40-day period that Jesus Christ spent in the desert without eating or drinking. Ramadan for Muslims is a period in which food and drink are restricted during sunlight hours as a way of promoting introspection and detaching from the ego. Hindus practice fasting regularly.

In the 20th century, therapeutic fasting reappeared in the West (USA and Europe) with a reclaiming of its medical applications. Currently it is one of the most relevant topics related to food and health (15).

Why is fasting so important?

With today’s over-eating, processed food consumption, and sedentary lifestyles we are surpassing our natural capacity for toxin elimination.

Our bodies are equipped with chemical and physical mechanisms that absorb nutrients and eliminate toxins. We have large organs such as the intestine, liver, kidneys, skin and lungs which function to keep our bodies clean.

Fasting facilitates the body’s detoxification and purification process.
  • Toxins are derived from both outside or inside the body. From the environment around us we are exposed to chemicals in the form of pollution, in food, household products, pesticides, herbicides, fungicides, bisphenols, phthalates, parabens, aluminum, lead, and so on.
  • Toxins also emerge from within the body via metabolic processes such as urea- a result of protein metabolization, and free radicals from metabolic processes of energy production. Fasting helps us to flush these toxins out of our bodies.

If we are not able to flush the toxins out, we also have defense mechanisms that protect us from their damaging effects such as fluid retention (oedema), fat binding (cellulite), or crystal deposits in joints, tissues or vascular walls.

Fasting facilitates the body’s detoxification and purification process:

  • When a person fasts, they don’t spend energy digesting and absorbing nutrients, giving those cells and organs a chance to rest.
  • This energy can then be used for elimination and cleansing processes: damaged cells, cellular detritus, micro-tumors, diseased tissues and altered proteins are eradicated during fasting.

Fasting physiology: what happens when we fast?

  • During the first 24 hours of fasting, we get energy from carbohydrate reserves, like the glycogen stored in our liver and muscles (20).
  • We get energy from fats for up to 40 days.
  • Very little protein is consumed. At first, proteins are consumed to provide the brain with glucose, but at one point the we begin using ketone bodies as fuel.
  • Fats are released into the bloodstream in the form of fatty acids. Some of these fatty acids are used as a source of heat and energy, and some are metabolized by the liver into ketone bodies.
  • Ketone bodies then become the new fuel source for our cells. These ketone bodies are much more efficient than glucose.

Health benefits of fasting

  • Reduced mitochondrial oxidative stress (9, 10, 19). This means that the function and health of our mitochondria, the source of energy present in our cells, is optimized.
  • The autophagy of damaged cells and tissues is activated (2): the body’s purifying capacity is enhanced, the extracellular matrix is cleansed, and inflammation mediators are eliminated.
  • There is a decrease in diseases associated with aging (4, 8, 9).
  • There is an increase in the production of neurotrophic factors which promote the formation of new neurons in specific regions of the brain, as well as in the synaptic connections between those neurons which already exist.
  • It has been observed that fasting alters hormone secretion and neuroendocrine patterns, thus decreasing stress hormone levels.
  • Fasting also helps to improve both mood and emotional balance. This occurs because intense and poorly managed emotions also act as toxins which flood our bodies and brains with neurotransmitters and hormones, which can be swept away during a fast.

Incorporating the practice of fasting is a good investment in health and well-being. It improves digestion and intestinal health (12), increases the sense of physical well-being and mental clarity (6), helps in weight control (3), increases defenses (5) and enhances feelings of vitality.

But, as always, it is important to be cautious and not get carried away by trends, marketing, or what has worked for others. It is necessary to use common sense and to make personalized decisions according to your own characteristics. Though uncommon, some people are intolerant to fasting- those who suffer from metabolic disorders and are unable to function in the absence of food, for example. Before beginning a fast, it is important that you understand your body well, and that you draw on that knowledge and apply common sense in deciding what and how you would like to progress.

Be cautious, apply common sense and don’t get carried away by trends or marketing.

How is fasting done?

There are several telling indicators that now would be the right moment for a cleanse: headaches, bad breath, dry mouth, a white coating on the tongue, heavy digestion, gas, eczema or acne, oedemas or swelling, cellulite, mental exhaustion, indecisiveness, nervousness, negativity….

Prepare well before starting a fast. Create clear objectives. Determine when you are going to begin, how long it will last, and how to see it through to the end.

Fasting is a self-care process, so it is best to plan it for a day when you can be relaxed and will have time to take a walk, read, or meditate.

Fasts can be short, medium or long:

  • A short fast can be a lengthened period of physiological cleansing which occurs while you sleep. Simply by skipping dinner or breakfast you should be able to prolong the the length of time that your stomach remains empty to roughly 14-16 hours. This type of fast can be fairly easy to include in your day-to-day. It can be carried out every day, every other day, or from Monday to Friday (giving yourself a break on the weekends).
  • An example of a medium fast is a 24-hour fast that is done once a week. In these 24 hours it is important to drink plenty of water in order to help your body flush away the toxins. Herbal tea and vegetable broth are also good alternatives to water.
  • An example of a long fast would be anywhere from 1 to 5 days at the changing of the seasons. Or, a 7 to 10 day fast that you commit to doing twice a year. It is crucial that you go into a long fast well-prepared. Give yourself time to enter the fasting state gradually, empty the pantry of all foods that you cannot eat, leave only those that you have decided to allow such as vegetables, herbal teas or shakes. Some fruits and vegetables can be good considerations for complete or partial fasts. The exit from a long fast should also be gradual. Food should be reintroduced in this order: fruits, vegetables, algae, good fats (avocado, coconut oil, nuts), grains, vegetable protein, and finally, animal protein.

During fasting, phlegm, dry mouth, a white or yellow tinged tongue, odorous perspiration, odorous urine, headaches and/or weakness may occur. These are signs of detoxification. Symptoms may worsen if you have an illness or medical condition, so be aware. Weight loss is also possible, especially in the first days of fasting, as retained water and toxins are being flushed out of your system.

Drinking plenty of water is important as it aids your body in the elimination of toxins. You can drink water with lemon, herbal teas, vegetable broths or seawater to replenish the necessary mineral salts.

Eating is often linked to emotions (it is common to eat more when feeling sad, anxious, frustrated, angry, etc). When you stop eating, some unpleasant or repressed emotions may come out. Fasting can be a good opportunity to recognize the relationship you have with food. It is one step further in your self-awareness.

Fasting is a revolution, for both body and spirit.

Intermittent fasting and caloric restriction are associated with improvements in or the prevention of most chronic inflammatory and degenerative diseases. The ketogenic diet, which is directly linked to fasting as it is a metabolic imitation of what happens in our organism when we fast and has shown significant benefits in: weight control (13, 14), diabetes, neurodegenerative diseases (11), cardiovascular diseases (7), epilepsy, and cancer. Fasting as a complementary treatment to chemotherapy has been shown to increase the benefits of chemotherapy and to reduce its side effects (1,17). It has also been found to halt the progression of certain types of cancer in animals (18).  If you want to know more about the ketogenic diet, have a look here.

Fasting is a very valuable tool for understanding yourself better. It gives you information regarding what you are capable of, and how you hold up to a challenge. In relation to self-improvement, by enduring discomfort or unpleasant emotions you are able to see how your body physically responds to demands. It is said that seeing is believing. Carrying out a fast allows you to progress further in your health-related beliefs.

We know that there are a lot of questions surrounding fasting, so we have prepared an article to answer your most frequently asked questions. Find the answers to all your fasting questions here.


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See references
1 Advising Women Undergoing Treatment for Breast Cancer: A Narrative Review. Lemanne D, Maizes V
2 Lysosomes Mediate Benefits of Intermittent Fasting in Cardiometabolic Disease: The Janitor Is the Undercover Boss. Mani K, Javaheri A
3 Intermittent Fasting: The Choice for a Healthier Lifestyle. Ganesan K, Habboush Y, Sultan S
4 Protein Restriction, Epigenetic Diet, Intermittent Fasting as New Approaches for Preventing Age-associated Diseases. Hanjani NA, Vafa M
5 Intermittent Fasting Confers Protection in CNS Autoimmunity by Altering the Gut Microbiota. Cignarella F, Cantoni C
6 Intermittent fasting uncovers and rescues cognitive phenotypes in PTEN neuronal haploinsufficient mice. Cabral-Costa JV, Andreotti DZ
7 Interventions to promote cardiometabolic health and slow cardiovascular ageing. Fontana L
8 Finally, a Regimen to Extend Human Life Expectancy. Larrick JW, Mendelsohn AR
9 Short-Term, Intermittent Fasting Induces Long-Lasting Gut Health and TOR-Independent Lifespan Extension. Catterson JH, Khericha M
10 Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Sutton EF, Beyl R
11 Effect of intermittent vs. daily calorie restriction on changes in weight and patient-reported outcomes in people with multiple sclerosis. Fitzgerald KC, Vizthum D
12 Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function during Homeostasis and Aging. Mihaylova MM, Cheng CW
13 Intermittent Fasting with or without Exercise Prevents Weight Gain and Improves Lipids in Diet-Induced Obese Mice. Wilson RA, Deasy W
14 Intermittent v. continuous energy restriction: differential effects on postprandial glucose and lipid metabolism following matched weight loss in overweight/obese participants. Antoni R, Johnston KL
15 Metabolic Effects of Intermittent Fasting. Patterson RE, Sears DD
16 Unraveling the metabolic health benefits of fasting related to religious beliefs: A narrative review. Persynaki A, Karras S
17 When less may be more: calorie restriction and response to cancer therapy. O’Flanagan CH, Smith LA
18 Starvation, Stress Resistance, and Cancer. Buono R, Longo VD
19 Marwan Maalouf, Patrick G. Sullivan. Ketones inhibit mitochondrial production of reactive oxygen species production following glutamate excitotxicity by increasing NADH oxidation. Neuroscience. 2007 Mar 2; 145(1): 256–264
20 Takagi, A. et al. Mammalian autophagy is essential for hepatic and renal ketogenesis during starvation. Sci. Rep. 6,18944; doi: 10.1038/srep18944 (2016).
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