What is fasting?
An ancient practice
Humans and animals have always practiced fasting. Often driven by lack of food or illness, it is today a voluntary practice.
It is an integral part of many religions such as Christianity, Hinduism, or Islam. Among Christians, for example, a fast is practiced during Lent. Fasters alternate complete fasts and lean days for 40 days.
Fasting was notably practiced during Antiquity, among the Greeks and Romans, for medical or spiritual reasons.
Hippocrate, considéré comme le « père de la médecine », vantait déjà ses mérites : « Quand le corps est chargé d’humeurs impures, faites-lui supporter la faim, elle dessèche et purifie ».
On indiquait la privation de nourriture pour prévenir ou traiter diverses maladies comme l’épilepsie. On lui reconnaissait aussi des vertus pour favoriser le processus d’autoguérison.
Sick or injured animals that instinctively stop eating are the best example.
A regenerative process
For many, fasting is a mysterious practice, often associated with hunger, illness, or weakness. But it is more of a global regenerative process, both physically, to purify and cleanse the body, and emotionally and energetically.
To listen | Our podcast on fasting with Dr. Lionel Coudron, a fasting specialist
From a medical perspective, fasting may help regenerate certain organs (liver, lungs, skin…) and stem cells, the progenitors of all cells in the human body.
How does it work?
Glucose deprivation
After 36 hours, the body has exhausted its glucose reserves. This first stage manifests as a feeling of hunger, fatigue, or heartburn.
In response, the body will produce glucose through glycogenolysis. This process breaks down liver glycogen into glucose. This further helps stabilize blood sugar levels.
The state of ketosis
Without sugar reserves, the body now relies on lipids rather than on carbohydrates to generate energy. After 36 to 48 hours, it taps into 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 primary source of energy.
During this phase, you may experience headaches, nausea and extreme fatigue. These symptoms are characteristic of an acidosis episode, a normal phenomenon related to the elimination of toxins.
The feeling of hunger disappears
Starting on day 6, the feeling of hunger is less noticeable. This is due to ketones, which are anorexigenic compounds or “appetite suppressants”. At the same time, they increase the production of neurotransmitters (dopamine, adrenaline, serotonin…), which are involved in the regulation of appetite.
New physical and mental energy
The disappearance of hunger is accompanied by renewed vitality and mental sharpness. Thanks to the stimulation of neurotransmitters, the faster experiences a boost of energy and a sense of well-being, even euphoria. The body stabilizes.
To listen | Our podcast on fasting with Dr. Lionel Coudron, fasting specialist
Refeeding
At the end of the fast, resuming eating causes the body to reuse glucose. It draws again on its sugar reserves to produce energy.
The benefits of fasting
Helps with weight loss
This is often one of the faster’s primary motivations. In the absence of calories, and because the body draws on its reserves, weight loss is rapid and occurs within the first few days.
As shown by this study, intermittent fasting appears promising for the treatment of obesity.
Regenerates the liver
Even though it remains active during the fast, the liver is less taxed than usual. This period of ‘rest’ allows it to regenerate, gain vitality and efficiency.
It speeds up detoxification and frees the organ from accumulated toxins. Finally, it may help relieve certain liver conditions such as cirrhosis.
Reduces inflammation
As shown by this study, fasting can have beneficial effects on inflammation. This practice may relieve rheumatoid arthritis and chronic inflammatory bowel diseases such as Crohn’s disease.
Among the ketones produced during fasting, beta-hydroxybutyric acid is anti-inflammatory.
Boosts cognitive function
Fasters often notice a boost in their brain activity and an improvement in cognitive functions such as memory and learning. Ketones have a neuroprotective effect and slow the aging of brain cells.
Furthermore, fasting supports neurogenesis, that is the generation of new neurons in the brain. This is why it is being studied as a potential treatment for neurodegenerative disorders such as Alzheimer’s disease.
Potentially anti-cancer
Le jeûne montre des résultats intéressants contre le cancer. D’une part, il prive les cellules cancéreuses de glucose, leur source principale de nourriture. Elles finissent donc par mourir.
To listen| Our podcast on fasting with Dr. Lionel Coudron, fasting specialist
On the other hand, it seems to enhance the effectiveness of treatments against cancer such as chemotherapy. Finally, it reduces their side effects, as shown by this study.
Different forms of fasting
Intermittent fasting
It consists of alternating periods of fasting and normal eating for a set duration. The digestive rest phases should last between 12 and 16 hours. It can take different forms. Thus, we distinguish:
- le jeûne intermittent 16/8 : manger seulement une partie de la journée ou sauter un repas (le petit déjeuner ou le dîner)
- le jeûne intermittent 5:2 : manger 5 jours par semaine et jeûner 2 jours
- le jeûne intermittent un jour sur deux
Dry fasting
Practiced over a short period of time, it involves abstaining from food but also from liquids.
It can be complete or intermittent, meaning it is practiced only during a specific period of the day.
Ramadan, for example, is a dry, partial fast that takes place from sunrise to sunset.
Water fasting
The practice is based on a liquid-only : water, herbal teas, broths… It is no longer possible to eat solid foods during a given period. It can be practiced for 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:
- troubles circulatoires
- maux de tête
- troubles de l’humeur
- mauvaise haleine
- nausées
- dyspepsie
Always fast under the supervision of a doctor.
Contraindications
On déconseille cette pratique aux personnes suivantes :
- femmes enceintes et allaitantes
- personnes souffrant d’insuffisance hépatique, rénale ou cérébrovasculaire
- personnes souffrant de troubles alimentaires (anorexie, boulimie…)
- en cas de faiblesse générale ou de cachexie
- en cas d’hyperthyroïdie
People on medication should be monitored by a doctor for the entire duration of the fast.
Maximum duration
The duration depends on the type of fast and varies according to weight, body fat, or the overall condition of individuals. It could last up to 40 days.
