We will review the 5 fasting stages, their occurring in the body and benefits. Note that the fasting stages by hour are given as a guide. Indeed, they are essentially valid for water fasting because we will enter these phases more quickly in dry fasting. Moreover, these durations vary from one individual to another but also according to the person’s level of activity.
5 stages of fasting
fasting stage 1: From 0 to about 4 hours after the last food intake
When we consume food, it goes through the digestive system, which will break it down into simple assimilable elements:
- Carbohydrates are broken down into simple sugars.
- Proteins are broken down into amino acids.
- Seeds are broken down into fatty acids.
In this first phase of the 5 fasting stages, these elements, such as sugars, will then be able to cross the intestinal barrier to reach the blood. Carbohydrates are an important source of energy for the body’s cells. Thus, when we eat, the body takes advantage of this to build up glucose reserves. This process is called gluconeogenesis, synthesizing glycogen from glucose in the liver and muscles. Only hepatic glycogen can be redistributed to the body’s other cells. On the other hand and in normal times, the blood sugar level, also called glycemia, must be between 0.7 g / liter and 1.4 g / liter. When we eat, the blood sugar level could largely exceed these values, especially after a copious meal.
Therefore, when we eat, the body triggers the production of a protein hormone called insulin which will have a hypoglycemic action. This protein will decrease the sugar level in the blood. Indeed, the role of insulin is to make sugar enter the cells and send a storage signal. The body will then transform the sugars in the blood into fat and store them in the adipose tissue. This process is called lipogenesis. Therefore, the blood sugar level will remain stable even after ingesting a lot of sugar. Then, blood sugar and insulin production will drop after a certain period without food intake. As we mentioned, the body will do everything possible to keep its blood sugar level above 0.7 g/liter to stay healthy. It will then trigger successively several mechanisms called hyperglycemic.
Commonly associated symptoms: drowsiness or sleepiness after very large meals.
“Carbohydrates are an important source of energy for the body’s cells.”
Stage 2: Approximately 4 to 16 hours after the last food intake
During this second fasting stage, the amount of blood sugar from the digestion of the last meal begins to drop, and the liver will start to release glycogen, the only form of carbohydrate storage in the body. The release of glycogen will peak about 6 hours after the last food intake. This glycogen is found in limited quantities in the liver and muscles and must be replenished regularly. When glycogen is broken down into glucose molecules for the body’s energy needs, this process is called glycogenolysis. During this phase, the body’s fuel released is glycogen and neoglucogenesis. If the body has difficulties functioning on these 2 mechanisms, it can trigger the production of adrenaline, a hyperglycemic hormone.
Commonly associated symptoms: Slight nervousness if adrenaline production, feeling of empty stomach, or dizziness if the faster is not used to fasting regularly.
Stage 3: About 16 to 32 hours after the last food intake
During this third phase of the 5 fasting stages, there are few glycogen stores in the liver and muscles. So these will drop rapidly. Another hyperglycemic mechanism is used to keep blood glucose levels constant: neoglucogenesis. Neoglucogenesis is the synthesis of glucose from non-carbohydrate compounds such as amino acids from proteins and fatty acids from fat reserves. The body will then use muscle tissue and fat to function. However, we quickly see a significant increase in the growth hormone level that will limit muscle tissue degradation in favor of fat degradation to avoid too much muscle loss. Contrary to the glycogen reserve, fats constitute a much more important glucose reserve for the body.
The process of breaking down consumed or stored fat is called lipolysis. The lipid stocks in the body are mainly triglycerides, composed of 3 fatty acids associated with a glycerol molecule. Triglycerides will then be broken down into glycerol, used for neoglucogenesis, and fatty acid, used directly by many body tissues as an energy substrate (without being converted into glucose). Except for the brain, because they can not pass the blood-brain barrier. Note that during a dry fast, without any water intake, fat consumption by the body will be faster to produce water endogenously (decomposition of fat into water). We will therefore enter the different phases more quickly in dry youth.
Commonly associated symptoms: Beginning of muscle and fat melting, decrease in energy and tension, a cleansing crisis such as skin rashes, urinary inflammation, cough, fever, nausea and vomiting, and continuous or pulsating headaches.
“Fat is an important reserve of glucose for the body.”
fasting stage 4: Approximately 32 hours to 24 days after the last food intake
Neoglucogenesis begins to decline significantly because insulin levels drop sharply. Indeed, the glucose produced through glucogenesis can no longer enter and be used by the cells without insulin. Therefore, glucose becomes a limited fuel for the brain and the body’s cells. The brain feeds essentially on glucose and cannot feed on fatty acids. Moreover, the cells cannot feed themselves with glucose because they lack insulin. Therefore, the body will produce a new fuel capable of making both the brain and the body function: ketone bodies.
Ketone bodies are produced from the metabolization of fats. We say that the body enters a state of ketosis, which means that it draws its energy mainly from ketone bodies and, to a lesser extent, from glucose. The entry into ketosis happens around 36 hours for a person in dry fasting and around 3 days for a person in water fasting. The important presence of ketone bodies will completely stop the degradation of proteins in favor of fats only. This accumulation of ketone bodies in the blood will acidify it and cause a decrease of the PH below 7.35 without going below a critical threshold.
This phenomenon is called the acidosis crisis. It is assumed that the phenomenon of significant autophagy, i.e., high autophagy, starts between 24 and 48 hours after the last food intake, depending on the type of fasting and the person. During this phase, we can consider that we have entered into “therapeutic” fasting (as opposed to hormetic fasting). Between the 4th and 7th day comes the compensation and balance phase, where mood improves, weakness disappears, and weight loss stabilizes.
Commonly associated symptoms: Strong breath due to the presence of ketone bodies. Muscle mass is maintained because the body no longer draws energy from muscle tissue, but fat loss continues. The acidosis crisis causes a general malaise with symptoms such as fever, low energy, susceptibility, nausea, and all the other symptoms mentioned in phase 3. The fasting person does not feel any hunger because he or she is fed endogenously by fats. The symptoms of the acidosis phase subside later, during the compensation phase. The return of appetite marks the end of phase 4.
Last fasting stage : Approximately 24 days or more after the last food intake
In this last phase of the 5 fasting stages, an overweight person will be able to fast longer than a slim person because they can fast as long as they have fat reserves. According to Dr. George F. Cahill, an obese person could therefore be able to fast for several months! Nevertheless, Water fasting is no longer recommended for all constitutions. Therefore, a fasting or so-called “Buchinger diet” is strongly recommended under appropriate medical supervision (see the Buchinger-Wilhelmi clinic).
Additionnal information on fasting for an obese person : Is fasting a new therapy? by Thierry de Lestrade, Line 7 to 34 on page 112.
If the fasting person continues beyond the depletion of fat resources, the body will again consume its proteins (muscle tissue and lean body tissue) to produce glucose. From that point on, the individual can put himself in real danger. Therefore, this will no longer be referred to as therapeutic fasting but starvation.
Commonly associated symptoms: Muscles will melt, and tissues will break down. If the person does not refeed, the outcome is the organism’s death.
Interested in fasting? Have a look at our other fasting articles:
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- Health, fasting and the immune system: is there a correlation?
- Fasting anti-aging: longevity & body regeneration
- Types of fasting & what’s right for you