Do you wonder how intermittent fasting works in your body? Here is the science-backed answer!
How Does Intermittent Fasting Work?
While intermittent fasting, you eat within a certain period and fast the rest of the time.
Various intermittent fasting schedules work, but the most popular is fasting within a time window of about 16 hours.
Thereby, you only eat between noon and 8 p.m. So your body can fast for 16 out of the 24 hours with an 8-hour eating period.
Moreover, fasting ensures that the gut and digestive tract can rest after 8 hours of sleep (or before that) for 8 hours a day.
To start with the 16/8 intermittent fasting program, you only have to skip breakfast.
Contrary to common belief, breakfast is not mandatory. Since your body injects you with a hormonal cocktail every morning, there is plenty of energy to thrive in your day.
Therefore, breakfast is only the food industry’s most important meal of the day. Since many people don’t have time to prepare food in the morning, highly processed products dominate breakfast.
Besides 16/8 intermittent fasting, the following intermittent fasting protocols are standard:
- One-Day Fasting (6:1 Diet) – you do not eat at all one day a week
- Alternate Day Fasting (ADF) – You eat one day and fast again the next
- One Meal A Day (OMAD) – 23/1 intermittent fasting, where you eat once a day
Why Does Intermittent Fasting Work?
During intermittent fasting, natural procedures work in the body. On the one hand, these processes affect weight loss. On the other hand, they can cause a variety of additional health benefits.
Perhaps you have heard that we lose weight while sleeping. Since insulin level drops during sleep, this is correct.
Thanks to conventional dietary advice, this is the only period allowing insulin to drop:
- Never skip breakfast
- Eat six times a day
- Snacks help you lose weight
Compared to the 1960s, when three meals a day was the norm, we now experience an imbalance between eating and fasting, turning us into fattening stock.
Intermittent fasting doubles the body’s fasting period from 8 to 16 hours and restores the natural balance between eating and fasting.
Since fasting is the most effective way to lower insulin levels, you lose weight.
Thus, intermittent fasting ends the body’s storage mode, emptying carbohydrate stores and ultimately burning body fat for energy.
This fat-burning process is called ketosis and, contrary to many myths, is a natural mechanism ensuring our species’ survival.
Thus, the body stores fat for a reason. When food is scarce, such as in winter or during fasting, the human body can live off body fat.
Due to elevated insulin levels, constant eating blocks the enzyme breaking down body fat (Meijssen et al. 20011).
Therefore, conventional calorie restriction can lead to weight loss in the short term but fat gain in the long run (Fothergill et al. 20162).
Accordingly, a study of 76,704 overweight men and 99,791 overweight women showed that 99.5% could not lose weight by restricting calories (Flides et al. 20153).
Thus, obesity is a hormonal, not a caloric imbalance.
Since carbohydrates and proteins stimulate insulin secretion, constant eating prevents weight loss.
Since prolonged fasting burns fat more efficiently, why should we fast for 16 hours?
There are two substantial reasons for 16 hours of intermittent fasting:
- Integration into everyday life
- Induction of autophagy
On the one hand, the 16 hours of intermittent fasting have practical reasons. If you skip breakfast or dinner, you have already reached 16 hours of intermittent fasting.
To eat only from noon to 8 PM can be easier than you might think because morning hunger can be unlearned.
Because you can always have dinner with your family, you can comfortably integrate this 16/8 schedule into everyday life.
Autophagy, on the other hand, is the intracellular recycling system in your body and the second reason for the 16 hours of intermittent fasting.
Moreover, autophagy’s discovery was such a scientific milestone that it was rewarded with the Nobel Prize (Levine et al. 20176).
When food is scarce, the body goes from growth into maintenance mode. Then it does not want to grow further but recycles broken cell parts.
Therefore, the following three nutrient sensors exist in the body, switching autophagy on and off:
- Insulin: Sensitive to carbohydrates and proteins
- mTOR: Sensitive to proteins
- AMPK: Sensitive to lack of energy in cells
So if the dietary energy supply – regardless of which macronutrient – to cells is interrupted, cells want to react sustainably and use disused cell parts to generate energy.
These sensors detect nutrient availability and stop autophagy as soon as you eat.
According to current research, you should not stimulate the nutrient sensors for approximately 14 hours to induce autophagy (Yang et al. 20177).
Thus, 16 hours of intermittent fasting make sense. However, you can induce autophagy faster through exercise and a ketogenic diet.
How Intermittent Fasting Works in the Body
As the previous discussion indicated, interesting processes happen in the body during intermittent fasting, which could enrich the understanding of biochemistry and medicine in the past years again and again by new realizations.
Nevertheless, we only touched on a fraction of the effects and benefits. For this reason, we dig deeper into the following processes that happen to your body during intermittent fasting:
1. Induces Autophagy
Vehicles must be maintained regularly. So does your body.
With this in mind, fasting is the best way to activate autophagy (Bagherniya et al. 20188).
Accordingly, the self-healing mechanism replaces broken cells with new ones and drains toxins from your body. As a result, autophagy can fight cancer, diabetes, liver, or autoimmune diseases.
Furthermore, research is increasingly deciphering that autophagy may also renew damaged proteins and organelles in heart cells (Sasaki et al. 20179).
Since it can also slow down the aging process, autophagy is probably the most convincing reason to fast for at least 16 hours (Gelino et al. 201210).
2. Reduces Inflammation
Aging is the accumulation of cell damage with a decreasing ability to repair it. As a result, aging causes a certain amount of inflammation in the body.
Recent studies suggest that fasting-induced autophagy can significantly increase the life span (Nakamura et al. 201811).
Therefore, intermittent fasting programs work as a treatment for age-related diseases.
Furthermore, intermittent fasting reduces the consumption of proteins, which positively impacts longevity.
With this in mind, it is precisely modern diseases such as arteriosclerosis, cancer, or type 2 diabetes characterized by too much protein and growth.
In addition to autophagy, which breaks down defective proteins and toxic protein accumulations, reduced inflammation in the body contributes to increased life expectancy.
Furthermore, ketosis during fasting lowers blood sugar and insulin levels, reducing inflammation and the body’s free radicals that cause disease.
Therefore, another recent study found that extending life expectancy is a primary health benefit of intermittent fasting (Catterson et al. 201812).
3. Improves Cognition
Intermittent fasting can also help the brain to reduce the accumulation of toxic proteins that promote dementia.
Accordingly, research suggests that in the early stages of dementia, the process of autophagy is significantly reduced (Li et al. 201713).
However, if the body burns ketones from fat stores instead of glucose from carbohydrate stores due to regular fasting or exercise, pathways improving learning and memory function are activated.
As a result, intermittent fasting can work against neurodegenerative diseases such as Parkinson’s or Alzheimer’s (Raefsky et al. 201714).
One of these messengers is the neuronal growth hormone BDNF, responsible for forming new nerve cells.
Therefore, high BDNF levels are also associated with increased intelligence and memory function.
When you release BDNF, your brain can form new nerve connections. Thus fasting can improve the memory of older people (Witte et al. 200915).
Furthermore, fasting activates the sympathetic nervous system, and the body releases adrenalin, cortisol, and growth hormone.
For this reason, many people report increased cognition and focus while fasting.
Therefore, studies have not found a reduction in cognition in people who fasted for two days (Liebermann et al. 200816).
Only breaking the fast allows your body to relax, and the focus fades.
4. Boosts Metabolism
Contrary to the widespread myth that intermittent fasting slows down metabolism, scientists have proven that it instead improves it (Drenick et al. 196417).
Because fasting releases growth hormones and adrenaline, our ancestors could prolong their search if they didn’t find food.
Therefore, they could ensure the species’ survival even during food shortages (Ho et al. 198818).
Consequently, intermittent fasting increases the efficiency with which your body can tap into body fat for energy.
Due to the release of hormones, such as noradrenaline, the body can also keep the basal metabolic rate up (Zauner et al. 200019).
5. Promotes Muscle Gain
Also, intermittent fasting works for bodybuilding. Above all, peak fasting – generally a 16/8 schedule – is widely leveraged to improve muscle gain.
With this in mind, exercising during a fasted state is vital to maximizing the benefits.
Contrary to common belief, muscles do not atrophy at all with fasting.
As we have already heard, intermittent fasting increases the release of growth hormones.
Thus, during fasting, muscle and bone mass are protected from degeneration (Rudman et al. 199020).
Accordingly, targeted intermittent fasting combined with appropriate exercise is a natural way to enhance muscle gain (Ho et al. 198821).
6. Puts the Body Into Ketosis
Ketosis is a metabolic state in which your body burns fat as a primary fuel.
When free fatty acids from body fat or food reach the liver, they are converted into ketones to provide energy for the body.
Since the body can only produce ketones from body fat during fasting, it’s the ultimate ketogenic diet.
Therefore, ketosis induced by intermittent fasting can burn fat reserves exceptionally fast (Paoli 201422).
Furthermore, ketosis helps regulate the appetite and stabilize blood sugar, supporting intermittent fasting and weight loss.
Accordingly, ketones’ energy does not lead to a drop in blood sugar levels, such as after carbohydrate-rich meals. Because ketones can also cross the blood-brain barrier, they provide lasting clean mental energy (Hallböök et al. 201423).
7. Burns Off Harmful Fat
On the one hand, intermittent fasting can help to shed off annoying subcutaneous fat.
On the other hand, studies suggest that it also burns off dangerous visceral fat more effectively than low-carb diets (Catenacci et al. 201624).
Visceral fat accumulates in and around vital organs, such as the liver, intestine, or pancreas.
They can cause severe ailments, such as non-alcoholic fatty liver diseases, type 2 diabetes, and cardiovascular diseases (Bray et al. 200725).
Since the liver is the first organ to deposit visceral fat, they significantly favor metabolic diseases such as insulin resistance.
8. Fights Insulin Resistance
In the 1960s, physicians already knew about the effectiveness of fasting as a treatment for insulin resistance (Jackson et al. 196926).
Accordingly, even current studies refer to intermittent fasting as a safe treatment for insulin resistance (Catenacci et al. 201627).
Insulin resistance is nothing more than a protective mechanism of the body against the vast amounts of insulin caused by our western pattern diet dominated by refined carbohydrates.
Besides fighting this causative hyperinsulinemia, intermittent fasting can increase the insulin sensitivity of cells.
Therefore, intermittent fasting can reverse type 2 diabetes, which diets alone usually can’t (Halberg et al. 200528).
9. Promotes Gut Health
Intermittent fasting schedules also work to improve gut health.
On the one hand, fasting periods permit your gastrointestinal tract to rest. On the other hand, it starves harmful gut bacteria.
But already shorter intermittent fasting periods work. Accordingly, a recent study suggests determining an extension of life expectancy with short irregular fasting periods at a young age.
In particular, reducing inflammation, which often originates in the gut, slows down the aging process.
Therefore, this study also states that intermittent fasting reduces age-related diseases and strengthens the intestinal wall (Catterson et al. 201829).
Furthermore, intermittent fasting thereby has the positive side effect of improving intolerances.
Nevertheless, there are many myths about intermittent fasting circulating on the net. Just as you don’t get tired or lose muscle mass during fasting, you won’t be plagued by cravings.
Accordingly, researchers at the University of Vienna have shown that the hunger hormone ghrelin decreases during fasting and remains low during prolonged fasting (Natalucci et al. 200530).
Also, blood sugar levels remain stable through gluconeogenesis, when the body burns fat for energy during fasting (Merimee et al. 197431).
Therefore, what happens during intermittent fasting in the body is natural. Would we exist today if nature designed humans to collapse after not eating for 16 hours?
Considering that the world record for fasting is 382 days, 16 hours without food are not rough and can help counteract modern diseases, such as Alzheimer’s, metabolic syndrome, or cardiovascular diseases (Stewart et al. 197332).
Frequently Asked Questions (FAQ)
How does intermittent fasting work for weight loss?
Intermittent fasting helps to deplete glycogen stores to burn body fat faster.
What does intermittent fasting do to your body?
It reduces inflammation, enhances weight loss and muscle gain, and can even help renew old cell parts.
How do you do intermittent fasting?
During intermittent fasting, you only eat during a specific time frame. For example, you eat between noon and 8 PM and fast for the rest of the day (and night).
How quickly does intermittent fasting work?
How quickly intermittent fasting works depends on your diet. If you are eating refined carbohydrates, you will have a hard time burning body fat at all. Low-carb diets amplify results.
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Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.
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