Chapter III – Fasting Physiology

The study of the changes induced by fasting in the body is extremely difficult and complex and can only derive from careful and repeated observation of the phenomena that occur during abstention from food, appropriately validated by scientific studies published on the subject.

It can be said that each single case contributes to add details in the clinical and therapeutic field and shows new extraordinary potentialities of fasting.

The effects of fasting are evident on all the cells of the organism, being al all forced to adapt to a new energy structure.

Analyzing in detail the main organs and systems of the human body, the DIGESTING APPARATUS is the one that benefits most from fasting, being in almost total functional rest, due to the absence of digestive phenomena.


The digestive organs play a very important role in the general energetic balancing of the organism; this is not adequately recognized by conventional medicine, despite recent scientific evidence.

The action carried out by the large intestine within the immune system is of particular importance;  as of today, the colon role is considered much more important than to be the simple vehicle of waste materials, as it results from classical physiology.

As a matter of fact, it has been shown that most of the immune phenomena occur at the level of the lymphoid tissue, associated with the mucosa of the colon.


Fasting radically intervenes in the physiology of the digestive system by progressively abolishing food-induced exocrine secretions such as gastric, pancreatic, biliary, and intestinal juices and reducing endocrine secretions related to digestive phenomena; this allows the regeneration of tissues damaged by inflammatory phenomena such as gastritis, sustained by food-induced acid hypersecretion.

Only the biliary flow is kept constant, or rather it is intensified by carrying toxic substances eliminated from the bloodstream through the liver filter, into the digestive tract.

In addition, fasting has a powerful anti-inflammatory action at all levels acting through the reduction of leptin production by the mucous membranes, a mechanism that feeds chronic inflammation.

After the first few days of fasting, evacuation activity is inconstant, sometimes with sudden discharges, and then regularizes during the week when bile secretions intensify, indicating good detoxification activity.


Fasting, together with the intake of pure lemon juice, is able to eradicate HELICOBACTER PYLORI from the stomach, thanks to the reduced production of mucus that does not allow adequate protection to the germ and to the improvement of mucosal immune reaction, such as the synthesis of IgA.


In all diseases of the gallbladder, pancreas, and biliary tract, fasting is a very valid measure, also adopted in conventional medicine as it practically puts these organs to rest through the elimination of digestive juices.

The effects on intestinal mucous membranes are extraordinary; they benefit from the reduced functionality to regenerate microvilli and fully regain barrier function and selective absorption capacity. In addition, the parietal immune phenomena of resistance to infection are enhanced and the synthesis of IgA class immunoglobulins is increased.

The existing bacterial flora at the intestinal level is almost completely removed to allow its reconstitution from scratch when restarting eating. At the end of fasting the intestine is, as matter of fact, in the condition of new birth, in which it must be colonized by bacteria for the first time; for this reason, the restart of feeding has the fundamental role of guiding the bacterial flora that will be produced after fasting.

The LIVER is the organ that exercises control over the entire metabolism during fasting. Unlike other organs, the liver is not at rest and it must act in providing for the elimination of toxins and manage the whole complex transition of metabolism, the control of glycaemia, glycogenolysis, glyconeogenesis, and the catabolism of fatty acids and ketone bodies. Nevertheless, the liver is able to detoxify and eliminate the toxins accumulated in the hepatocytes and those extracted from the blood, by transporting them to the intestine via bile.

Hepatocytes that have been damaged due to toxic or infectious factors, such as hepatitis viruses, are able to regenerate and eliminate the pathogen that infects them. The mechanism of this extraordinary effect of fasting seems to be due to the increase in the elimination of damaged cells (APOPTOSIS) and to the simultaneous increase in the replication of the replacement cells, which allows a quick replacement of the necrotic hepatocytes.

The constant biliary flow stimulates and keeps the intestinal activity active throughout the fasting period.

Sometimes in subjects with hepatic impairment, transient signs of hepatoxicity, such as a slight scleral subterus, may occur due to the temporary inability of the hepatocyte to cope with the double toxic and metabolic load. In these cases, it is necessary to wait as long as necessary to allow the cells to get rid of the accumulated toxicity.

Evaluating the evolution of liver detoxification processes, fasting proves to be a useful indicator of functional reserve in subjects with a significant reduction in organ function.


The kidney is a central organ in fasting purification processes, especially in the first phase. During the first few days, a high protein catabolism occurs; it is necessary to convert amino acids into glucose molecules and this leads to an increase in the production of waste, such as urea nitrogen and uric acid that the kidney must eliminate.

The kidney plays another important role in hydro-saline re-balancing, characterized by the elimination of the excess in sodium and liquids improperly retained in the tissues.

Similar re-balancing effects are also induced to reduce the excess in acidity in the body. Thanks to the exchanges in the renal cells, a significant elimination of acidic valences (hydrogenions) which are discharged into the urine, occurs.


Finally, the kidney also participates in the regulation of glycaemia through the process of gluconeogenesis starting from protein substrates and in the balance of ketone bodies, by eliminating them through the urine in case of excessive production.

The effects of renal purification processes are evident in the emission of dark and foul-smelling urine, sometimes with the characteristic smell of a drug.

The HEART and the entire cardiovascular system greatly benefit from the combined actions of fasting, so much so that some researchers claim that a real cardio-protection is generated.

First of all, the activity of the myocardium is reduced thanks to the reduction in blood pressure. Other favorable aspects are linked to the reduction in plasma sodium, in adrenergic tone and circulating catecholamine, in platelet aggregability factors that make the blood more fluid and cholesterol and triglycerides that help prevent the development of atherosclerotic lesions. All these aspects contribute to a  myocardial remodeling effect that improves functional performance. This improvement is particularly evident in people suffering from decompensated heart disease, inducing a significant recovery of cardiac function.

Similar effects are induced in all vascular diseases and they are particularly evident in peripheral arteriopathies, where there is a significant reduction in arterial plaques that hinder blood flow, with a consequent improvement in circulation.

The LUNGS undergo a drastic purifying process, characterized by the elimination of toxic substances accumulated in the alveoli and due to the consequences of cigarette smoke, air pollution, or toxic substances used for professional activities.


The effects of this process are particularly evident with the increase in sputum, which takes on a sticky, dense and foul-smelling character that remains for several days, especially in the morning. Similarly, abundant nasal and nasopharyngeal secretions can also be produced. In these cases, it is advisable to continue fasting until the secretions have normalized.

MUSCULES, during fasting, are in a favorable metabolic situation due to the ancestral and genetically determined need to ensure maximum functionality in order to guarantee escape, attack on prey, or a long journey in search of food. For these reasons the muscle tissue has a stock of glycogen that is used exclusively on-site to support the initial phase of fasting; i.e. unlike the liver glycogen that can be introduced into the bloodstream for glycemic regulation, this stock is intended for the production of energy for muscle cells only.

In the subsequent phase, the energetic apparatus of the muscle is rapidly converted to burn ketone bodies and fatty acids which, being high energy molecules, put the muscle cell in a high performance condition.  Moreover, fat burning is a process with a low oxidative load.

Therefore, it seems appropriate during fasting to stimulate moderate muscle activity by walking or swimming.

The CENTRAL NERVOUS SYSTEM is increasingly being characterized as one of the target organs of fasting because of the many actions that interact at various levels to restore full neuronal function and contribute to the state of neuropsychic well-being that accompanies fasting.


The nerve cell, which in normal conditions uses mainly glucose as an energetic substrate, is perfectly adapted during prolonged fasting to also use lipid-derived ketone bodies, which also involve a reduced production of free radicals and oxidative stress.

First of all, the favorable effect of the reduction in stress and adrenergic tone must be considered, which, together with the production of growth factors for cells (BDNF, GDNF), promotes neuroprotective and neuro rigenerative effects.

In addition, there is a widespread increase in the production of neurotransmitters such as serotonin, dopamine and acetylcholine, with a consequent improvement in their related functions. Of great clinical interest is the intense local anti-inflammatory effect that occurs due to the marked reduction of leptin, primum movens of inflammatory reactions in the CNS.

In conclusion, it can be said that nerve cells are subjected to impressive depurative and regenerative phenomena that make them more suitable to face new stress and stressful stimuli.