Intermittent fasting is the type of diet which alternates between periods of food and fasting.
While there are many forms of intermittent fasting, most consist of escaping from food during periods of 16 to 24 hours at a time.
During the implementation of fasting, your body goes through a fast feeding cycle that is characterized by changes in your metabolism and hormonal rate.
This diet cycle improves metabolic health as well as other health benefits.
1. Fed state
Diet begins in the first hours after eating that your body digests and absorbs nutrients from food.
During this time, your blood sugar increases and greater quantities of insulin are secreted. Insulin is a pancreatic hormone that transfers glucose from your bloodstream to your cells (1).
How much insulin is released depends on the composition of your diet, how much carbohydrate you eat and how sensitive your body is to insulin (2).
Additional glucose (sugar) is stored in the liver and muscles in the form of glycogens. Glycogen is your primary form of carbohydrates stored in your body and it can be transformed into sugar as an energy source when needed (3).
At the same time, levels of other hormones, including leptin and ghrelin, are changing as well.
Please note that the quick feeding cycle is readjusted to the feeding state immediately after eating food during fasting.
Furthermore, the quantity and composition of your food affects the duration of your body resides in the state of food.
2. Early fasting state
About 3 4 hours after eating, your body turns into an early state of fasting, which lasts for about 18 hours after eating.
During this stage, your blood glucosa and insulin levels begin to decrease, resulting in a conversion of glycogen into glucose (sugar) to be used as energy (1).
Towards the end of this phase, your body will progressively consume all the glycogen reserves of the liver and starts looking for another source of energy.
This intensifies lipolysis, a process in which the triglycerides of adipose tissues are decomposed into smaller molecules that can be used as an alternative source of energy (7).
Your body also uses amino acids as an energy source, which are the building blocks of protein.
A lot of common types of intermittent fasting, like the 16/8 method, cycle from the not-fasting or eating phase to the early fasting phase.
3. Fasting state
The fasting period lasts approximately 18 hours to 2 days of periodic fasting.
At this stage, your glycogen reserves in the liver have been consumed, and your body begins to decompose the protein and fat reserves for the energy source.
This results in the production of ketone body, a type of molecule produced during the decomposition of fats for energy (8).
This also causes your body to transform into ketosis, a metabolic state in which your body uses fat as a primary or primary source of energy (9).
However, the transition to ketosis may not take place immediately when you enter the state of fasting, but probably later (10).
As with the state of fasting generally, the amount and composition of your normal diet and last meal, as well as individual differences, affect the speed at which you enter ketosis.
Some of the more common symptoms of ketosis include:
Ketosis can also be achieved by other methods, for example, by following a ketogenic diet, which implies a remarkable reduction in your carbohydrate intake (12).
Please note that ketosis is different from ketoacidosis, which is generally a dangerous diabetic condition that occurs when your blood becomes too acidic (13).
In addition, note that forms of intermittent fasting, the duration of which varies between 12 and 18 hours a day, may not reach this state, Because ketosis cannot be achieved with less than 24 hours of fasting, unless you also follow a diet that is very low in carbohydrates.
4. Long-term fasting state (starvation state)
During times of fasting, your body goes into a long-term state of fasting, which usually occurs about 48 hours after taking food. Some called it a state of starvation.
Your kidneys are also still producing glucose through a process known as gluconeogenesis, that serves as the major power source for the brain. Ketones also supply energy to the brain at this stage (1, 15).
The break-down of branched-chain amino acids (BCAAs), that are three of the essential amino acids, is also reduced to help keep muscular tissue in the body (1).
Please note that long-term fasting is not recommended for most people and should only be monitored under medical supervision.
While implementing intermittent fasting, Your body goes through many stages of the rapid diet cycle, depending on how long you fast.
The four stages of intermittent fasting include the state of diet, the state of early fasting, the state of fasting and the state of long-term fasting or the state of famine.
Each stage varies depending on the primary energy source used for the body, as well as how it affects your metabolism and specific hormone levels.
If you have any basic health problems or if you are taking any type of medication, be sure to check with your doctor or health care professional before you begin intermittent fasting.
Also, remember that prolonged fasting should only be carried out under medical supervision.