What is fasting?
An ancient practice
Humans and animals have always practiced fasting. Often driven by food shortages or illnesses, it is now a voluntary practice.
It is an integral part of many religions such as Christianity, Hinduism, or Islam. Among Christians, for example, fasting is observed during Lent. Fasters alternate between full fasting and lean days for 40 days.
Fasting was notably practiced during Antiquity, among the Greeks and Romans, for medical or spiritual reasons.
Hippocrates, considered the “father of medicine,” already praised its merits: “When the body is burdened with impure humors, make it endure hunger, it dries and purifies“.
Food deprivation was prescribed to prevent or treat various diseases such as epilepsy. It was also recognized for virtues that promote the process of self-healing.
Sick or injured animals that instinctively stop eating are the best example.
A regeneration process
For many, fasting is a mysterious practice, often associated with the idea of hunger, illness, or weakening. However, it is more of a global regeneration process both physically, to purify and cleanse the body, and emotionally and energetically.
Listen to | Our podcast on fasting with Dr. Lionel Coudron, fasting specialist
From a medical standpoint, fasting contributes to the regeneration of certain organs (liver, lungs, skin…) and stem cells, which are the mothers of all cells in the human body.
How does it work?
Glucose deprivation
After 36 hours, the body has exhausted its glucose reserves. This initial phase results in a sensation of hunger, fatigue, or stomach aches.
In response, the body will produce glucose through glycogenolysis. This process breaks down liver glycogen into glucose. It still helps to stabilize blood sugar levels.
The ketosis state
Without sugar reserves, the body now relies on lipids rather than carbohydrates for energy. After 36 to 48 hours, it draws from fat stores and enters a state known as “ketosis.”
Fats are broken down to produce ketones, fuels for the brain and muscles. As ketone levels rise, they replace glucose as the main energy source.
During this phase, you might experience headaches, nausea, and extreme fatigue. These symptoms are characteristic of a crisis of acidosis, a normal phenomenon related to toxin elimination.
Hunger sensation disappears
From the 6th day, the sensation of hunger is less present. This is due to ketones, which are anorexigenic, or “appetite-suppressing” compounds. Simultaneously, they increase the production of neurotransmitters (dopamine, adrenaline, serotonin…), which are involved in appetite regulation.
New physical and mental energy
The disappearance of hunger is accompanied by newfound vitality and mental alertness. Thanks to the stimulation of neurotransmitters, the faster experiences a surge of energy and a sense of well-being or even euphoria. The body stabilizes.
À écouter | Notre podcast sur le jeûne avec le Dr Lionel Coudron, spécialiste du jeûne
Food reintroduction
At the end of the fast, food reintroduction leads to the reuse of glucose by the body. It again draws from sugar reserves to produce energy.
The benefits of fasting
Helps with weight loss
It is often one of the first motivations for fasters. In the absence of calories, and because the body taps into its reserves, weight loss is rapid and begins within the first few days.
As demonstrated by this study, intermittent fasting appears promising for the treatment of obesity.
Regenerates the liver
Even though it remains active during fasting, the liver is less stressed than usual. This period of “rest” allows it to regenerate, gaining vitality and efficiency.
It accelerates detoxification and frees the organ from accumulated toxins. Finally, it can help alleviate certain liver pathologies such as cirrhosis.
Reduces inflammation
As shown in this study, fasting can have beneficial effects on inflammation. This practice could relieve rheumatoid arthritis and chronic inflammatory bowel diseases like Crohn’s disease.
Among the ketones produced during fasting, beta-hydroxybutyric acid is anti-inflammatory.
Stimulates cognitive functions
Fasters often notice a stimulation of their brain activity and an improvement in cognitive functions such as memory and learning. Ketones have a neuroprotective effect and slow down the aging of brain cells.
Moreover, fasting supports neurogenesis, which is the generation of new neurons in the brain. This is why it’s being studied as a potential treatment for neurodegenerative disorders like Alzheimer’s disease.
Potentially anti-cancer
Fasting shows interesting results against cancer. On one hand, it deprives cancer cells of glucose, their main source of nourishment. As a result, they eventually die.
À écouter | Notre podcast sur le jeûne avec le Dr Lionel Coudron, spécialiste du jeûne
On the other hand, it seems to enhance the effectiveness of anti-cancer treatments like chemotherapy. Finally, it reduces their side effects, as shown in this study.
The different forms of fasting
Intermittent fasting
It consists of alternating periods of fasting and normal eating for a determined duration. The digestive rest phases should last between 12 and 16 hours. It can take different forms. Thus, we distinguish:
- 16/8 intermittent fasting: eating only part of the day or skipping a meal (breakfast or dinner)
- 5:2 intermittent fasting: eating 5 days a week and fasting 2 days
- every other day intermittent fasting
Dry fasting
Practiced over a short period of time, it involves abstaining from food but also from liquid.
It can be complete or intermittent, meaning practiced only over a given period of the day.
Ramadan, for example, is a dry and partial fast that takes place from sunrise to sunset.
Water fasting
The practice is based on a diet solely liquid: water, herbal teas, broths… It is no longer possible to eat solid foods during a given period. It can be practiced over several consecutive days or alternated with a day of normal eating.
Side effects and contraindications
Side effects
Stopping food intake and detoxifying the body can cause certain side effects:
- circulatory disorders
- headaches
- mood disorders
- bad breath
- nausea
- dyspepsia
Always practice fasting under medical supervision.
Contraindications
We do not recommend this practice for the following people:
- pregnant and breastfeeding women
- people suffering from liver, kidney, or cerebrovascular insufficiency
- people suffering from eating disorders (anorexia, bulimia…)
- in cases of general weakness or cachexia
- in cases of hyperthyroidism
People on medication should be monitored by a doctor throughout the fasting duration.
Maximum duration
The duration depends on the type of fasting and varies according to weight, fat mass, or the general condition of individuals. It could last up to 40 days.
