Fasting: how does it work?

Periods of fasting with deliberate restriction of solid food intake is practiced worldwide, mainly based on traditional reasons, cultural or religious. Few doctors were interested in the consequences of fasting on the body.

 

Many naturopaths have, however, hastened to advocate fasting in many affections. Herbert SHELTON, heir to DEWEY and TANNER, was an important activist of the fast, popularizing natural methods. He published in 1934, “The Science and Fine Art of Fasting”. It is the Russian school which, in Europe and in the post-war period, has carried out an impressive series of therapeutic fasts under medical supervision. Their publications have unfortunately not crossed the iron curtain and have not benefited from popularization at that time.

 

These studies have shown remarkable improvements in certain conditions such as diabetes mellitus ,m rheumatoid arthritis and other rheumatic , high blood pressure (hypertension) , asthma , the heart failure or allergy . “Fasting stimulates the healing powers of the organism”.

 

In more recently Dr. Otto Buchinger was the promoter of a hand and gave his name to two clinical fasting while Professor Valter D. Longo , biogérontologue published disturbing experiences on cancer in mice. Finally a scientific synthesis was carried out in 2013, but it remained confined to the German language…

 

Some metabolic notions

 

During a total fast with beverages (to avoid dehydration), no nutrients can be used or stored. The organization In order to maintain normal sugar levels in the blood, the body and then in liver reserves, glycogen (storage form of sugar), the breaks and releases glucose into the circulation.

 

This process, called gluconeogenesis , which is stimulated by cortisol (secreted during stress), is essential for maintaining normal glucose concentration in the blood between meals. This is essential for the  brain , which does not contain glycogen and feeds mainly on glucose for its operation. The table below shows the speed of use of the energy substrates.

The lipids circulating in the blood, in the form of fatty acid free and are stored as triglycerides in adipose tissue They constitute 77% of total energy content, about two months of energy stock. It is the main reservoir of energy, and the main source of energy during fasting.

 

The proteins circulating in the form of amino acids , is stored in the muscles and constitute 22% of the total energy of the body. Source of glucose for the brain during fasting, they are used as a last resort, once the other energy stocks run out. These stocks are totally unusable because deadly anomalies occur before the stock depletes (When 50% of the reserves were used during the fast).

 

The insulin and glucagon are the main hormones which depend the back and forth between anabolism and catabolism , but the adrenaline , the cortisol and growth hormone are also involved in the metabolism of nutrients.

 

What is going on When man stops eating?

 

There are typically three phases shown schematically in the figure below. The fourth phase concerns the prolonged fasting beyond 3 weeks and is not indicated as therapeutic.

 

The first phase is physiological

 

It corresponds to an absence of food intake lasting from twelve to 24 hours to 4/5 days. The body draws glucose from its liver reserves to maintain normal blood sugar levels. The depletion of glycogen stores results in a lowering of the blood sugar required by the brain. The only source of the body’s glucose becomes the gluconeogenesis , which produces glucose from amino acids for muscle protein. It is clear, however, that this situation can not continue, as protein melt is too fast and incompatible with prolonged survival. An adaptation aimed at saving proteins (especially amino acids capable of supplying glucose). This transition is progressive and results in a steady decrease in the concentration of glucose and its renewal.

 

The secondstage is “short fasting”

 

It corresponds to fasting ranging from 1 to 4 days. Normal. The depletion of glycogen stores results in a lowering of the blood sugar required by the brain. The only source of the body’s glucose becomes the gluconeogenesis , which produces glucose from amino acids for muscle protein. It is clear, however, that this situation can not continue, as protein melt is too fast and incompatible with prolonged survival. An adaptation aimed at saving proteins (especially amino acids capable of supplying glucose). This transition is progressive and results in a steady decrease in the concentration of glucose and its renewal.

 

The third phase is the “prolonged fast”.

 

This phase begins around the 5th or 7th day of fasting and can last several weeks. This phase is characterized by a much less marked protein loss (from about 4 g nitrogen / day to week 2) and stable.The main change is the significant rise in plasma concentration of ketone bodies . Because of this elevation, the brain oxidizes much less glucose. This leads to a decrease in protein degradation, and allows protein sparing especially of muscle protein mass.

 

Phases I and II correspond to the introduction of protein-sparing mechanisms related to the progressive and sustained increase in the utilization of fatty acids and ketone bodies as energy substrates.

 

The fourth phase (or the limit of adaptation to fasting)

 

This terminal has only been studied in animals, particularly in the emperor penguin, including Yvon Le Maho.

 

Fatty acids and ketone bodies collapse in the plasma, while blood sugar rises, and protein destruction is accentuated. This occurs while about 20% of the lipid reserves remain. If this third phase is not irreversible, it is nevertheless a major step involving hospitalization when it is observed in humans.

 

Beyond a critical consumption of proteins, the prolongation of the fast will be responsible for a significant mortality.

 

A medical follow-up becomes vital from the 4th week, depending on the state of health, the conditions of the fast and the nature of the reserves at the start of the fast. As soon as the blood sugar goes up, it will be necessary to stop fasting to avoid protein losses and muscle wasting. The lipid reserves of the individuals allow to better support the fast but are deceptive to evaluate a significant loss of proteic which is the decisive factor to stop the fast without harmful consequences for the organism.

 

These precautions could not be taken for the IRA prisoners in 1981; They had refused medical assistance. Bobby Sands died after 66 days of fasting. Nine of his fellow prisoners died after 59 to 73 days of hunger strike.

 

A prolonged fast beyond a certain length of time will inevitably cause death. This duration varies according to the individual and can reach more than 85 days.

 

An adult of 1.70 m, weighing 70 kg, has about 15 kg of fat reserves, which, if it is healthy, holds forty days before the depletion of the proteins stored in the muscles heart).

 

Fasting under medical supervision rarely exceeds three weeks and is often of a duration of 2 weeks thus avoiding any risk of damage to the integrity of the organism.

 

Alternate fasting diets (a small meal every 12 or 36 hours) did not show any obvious evidence and remained poorly supported with a lingering feeling of hunger.

 

Clinical effects

 

A synthesis of clinical studies shows that fasting is often accompanied by an increased level of vigilance, an improvement in mood, a subjective sense of well-being, and sometimes euphoria.Improvements in mood, alertness and a sense of tranquility correspond to an effect on depressive symptoms observable between the second day and the seventh day of fasting. The study of Li confirms, in 2013, on 30 patients, the improvement of the metabolic syndrome. The weight loss is about 6 kgs on average and the blood pressure decreases moderately. Biochemical changes are beneficial on lipids, some hormones.

 

There is considerable empirical and observational evidence that medically supervised fasting (fasting healing, nutritional intake of 200-500 kcal per day) with periods of 7 to 21 days is effective in the treatment of rheumatic diseases, syndromes Chronic pain, hypertension and metabolic syndrome. The beneficial effects of fasting followed by the vegetarian diet in rheumatoid arthritis are confirmed by controlled randomized trials. Thus, the improvement or prevention of most chronic degenerative and chronic inflammatory diseases is now a classic indication of fasting.

 

Another beneficial effect of fasting is linked to the improvement of the lasting change of lifestyle and the adoption of a healthy diet, possibly by the stimulation of the mood induced by fasting.Several identified fasting mechanisms indicate its potential health-promoting effects, for example, fasting induced neuroendocrine activation and hormonal stress response, increased production of neurotrophic factors, reduced mitochondrial oxidative stress, general decrease in associated signals To aging. Its evaluation in NASH or non-alcoholic steatohepatitis appears promising in the absence of drug treatment with the difficulty of applying hygiene-dietetic rules and regular physical exercise.

 

Intermittent fasting may also be useful as an accompanying treatment during cancer chemotherapy. However, caution should be exercised in this indication for Professor Longo and should be applied only after the consent of the oncologist in charge of the patient, who should not be undernourished or carrying a metabolic, renal, hepatic or renal disease scalable.

 

Fasting treatment can therefore contribute to the prevention and treatment of chronic diseases and should be evaluated in more detail in controlled clinical trials in order to convince the entire medical community of the benefits of this nutritional approach, which may appear shocking in Certain indications including oncology.

 

Some references to go further

 

  • Michael Boschmann, Andreas Michalsen, “Fasting Therapy – Old and New Perspectives”, Forsch Komplementmed 2013;20:410–411 DOI: 10.1159/000357828.
  • Xavier Leverve et Jacques Cosnes, “Traité de nutrition artificielle de l’adulte”, Springer Editions, Édition : 2nd, 2001, 957 Chapitre 28 Physiologie du jeûne (B. Beaufrère, X. Leverve) », p. 322-333.
  • Lauralee Sherwood et Alain Lockhart, “Physiologie humaine”, De Boeck; Édition, coll. « ANAT.PHYSIO », 2006, p. 563-564.
  • Oshima J & MartinG.M (2016), “Ageing: Dietary protection for genes”, Nature ; doi:10.1038/nature19427.
  • Éric Le Bourg, “La restriction calorique, un moyen de retarder le vieillissement et d’augmenter la longévité ?”, La Presse médicale, vol. 34, n°2,‎ 2005 p 121-127.
  • Lizzia Raffaghello, Fernando Safdie, Giovanna Bianchi, Tanya Dorff, Luigi Fontana et Valter D. Longo, “Fasting and differential chemotherapy protection in patients”, Cell Cycle, vol. 9, n°22,‎ 15 novembre 2010, p. 4474-4476.
  • Sylvie Gilman et Thierry de Lestrade, <href=”http://www.viadecouvertes.fr/pages/fr/reference.php?id=113″ target=”blank”>“Le jeûne, une nouvelle thérapie ?”, Documentaire, ARTE Thema France, Via Découvertes Production,‎ 2012.