FASTING AND ITS BENEFITS
Fasting is an age-old practice that has become popular in the West, particularly through the democratization of intermittent fasting , which is now quite widespread.
But there's this paradox : eating is necessary to be fit and healthy, so why would food deprivation be beneficial to your body?
Note : the mention of "fasting" without further specification will refer to water fasting.
WHAT IS FASTING?
Definition
Fasting is a voluntary period of prolonged abstinence from food (and sometimes water), long enough to cause a change in metabolic state .
After 8-16 hours without calories (the time varies depending on your metabolism and diet), your body uses up available sugars (glucose) and switches to a different energy source using stored reserves.
Any significant caloric intake (more than 50 kcal) interrupts the fasting state.
There are several types of fasting:
Only water and non-caloric drinks (tea, black coffee without sugar) are allowed.
This is the strictest form of fasting: no food, no liquids. For example, during Ramadan , practitioners fast completely from sunrise to sunset.
The consumption of very low-calorie foods is permitted (broths, soups, fruit juices, smoothies, etc.), in moderation, so as not to completely break the fast.
Why fast?
The goal is to inflict a moderate state of stress on your body in order to train it to effectively activate its protection and repair mechanisms, such as autophagy and the use of your fats as energy reserves, which it never uses in times of abundance.
Similar to physical training where you apply stress to your body in order to trigger adaptation mechanisms that will make it gain muscle and strengthen it.
It is not the absence of stress that improves your health, but your body's ability to respond to it .
Another benefit of depriving yourself of food is to increase your insulin sensitivity by putting less strain on it.
When you digest food, your insulin levels rise to allow glucose to enter your cells. Constant and prolonged use of this hormone is associated with an increased risk of health problems such as diabetes , weight gain , and cardiovascular disease .
To better understand insulin, I invite you to read this article which explains its role and impact on your body in simple terms.
HOW CAN YOUR BODY FAST?
Our current way of life is very different from that of our ancestors.
Thousands of years ago, humans lived in alternating periods of food abundance and scarcity: they therefore developed a physiological adaptation to survive when food became scarce.
It is this evolutionary process that allows you to fast even today.
More specifically, your body has three main energy reserves :
Stored in the liver and muscles. It is a fast but limited energy source (approximately 24 hours of maximum autonomy).
Your body fat. It's a more expensive energy source to obtain, but it represents tens of thousands of calories, allowing you to sustain yourself for several weeks , even if you're thin.
Your muscles. This is a last resort reserve that will be rarely used by your body. You will trigger its use in the event of a long fast (more than 24 hours) or during prolonged intense efforts without carbohydrate intake (marathon for example).
You would have to find yourself in a situation of extreme scarcity to use up these reserves that allow you to last several weeks without eating anything.
We can therefore deduce that our body is not designed for a constant supply of food but to alternate between cycles of digestion and rest.
Fasting restores this balance, allowing your metabolism to function better no matter what state you find yourself in .
THE PHASES OF FASTING
The length of time you are deprived of food will have a different impact on your metabolism depending on its duration.
The glucose from the meal is used directly as energy by your cells.
Once used, the excess is then stored in your liver and muscles. When these reservoirs are full, what remains will be converted into fat.
Your body has finished absorbing the nutrients from the last meal, your blood glucose is dropping.
To maintain a stable blood sugar level to fuel your brain, your liver releases its glycogen reserves (stored sugars).
It is during this phase, around the 12th hour, that fat burning begins to slowly accelerate.
Glycogen stores are now depleted.
To preserve your body's proteins (muscles), your liver begins to convert stored fats into ketone bodies .
Your brain starts using ketones as its primary fuel, which drastically reduces the need for glucose.
Ketosis is fully established, providing most of the energy to the brain and muscles.
Your glucose requirement is minimal and will be supplied by the use of proteins from your muscles, essential for red blood cells and some tissues.
Although your body uses some protein, growth hormone secretion increases massively to protect muscle mass and tissue integrity.
The indicated durations are approximate and are there just to give you a general idea of the different phases you go through depending on your fasting time.
DRY FASTING
Unlike water fasting where you can drink water, dry fasting goes further by excluding the ingestion of any liquid .
What impact will this have on your body?
In addition to the various adaptations due to lack of food, when you don't drink, your body is forced to produce its own water from its internal tissues, mainly through the oxidation of fats.
This is what is called metabolic water (or endogenous water ).
What are the advantages?
Because the body uses fat not only for energy but also for water, the loss of adipose tissue (the fat in your body) is faster than during a water fast.
Some believe that one day of dry fasting is equivalent to three days of water fasting in terms of cell regeneration. This remains a subject of debate, but dry fasting is thought to induce a deeper state of autophagy than water fasting.
Bacteria and viruses need external water to multiply. Dry fasting creates a hostile environment for pathogens, which is why the practice of fasting during Ramadan is often described as purifying the body of toxins .
As your body switches more quickly to using fats and accelerates ketosis, it also reduces the need for glucose more quickly and therefore decreases the need to break down proteins compared to a water fast.
Without external water intake, your body will seek moisture where it stagnates: it will therefore draw out your swelling and edema to hydrate itself.
Furthermore, this lack of water creates pressure that forces your cells to prioritize recycling your diseased or inflamed tissues to recover resources.
To put it simply, dry fasting can be considered a kind of "accelerated version" of water fasting.
The limits
Since dry fasting is much more intense, you generally wo n't exceed 24 hours in this state without prior preparation and monitoring.
It is also very important to take care of your exit from fasting when you practice it (do not eat and drink too much at once when breaking the fast, but do it little by little).
How can I break my fast without putting undue stress on my body?
CONCLUSION
You better understand why depriving yourself of food can, paradoxically, be beneficial for your health and longevity.
Of course, it is important to do it in a controlled, moderate way, without going to extremes, and to find a fair balance between abundance and scarcity.
FAQ
That's the number one fear, but your understanding of human body physiology is well done.
During a fast, your body secretes massive amounts of growth hormone to protect your lean tissues. Your body isn't stupid: it burns fat first before attacking your muscles.
Muscle loss only becomes a real risk if you practice prolonged fasting without any physical activity or if your body fat percentage is already extremely low .
It all depends on the objective. For a low-intensity session, fasting is ideal for optimizing fat oxidation.
For a strength or high-intensity session, it's possible, but your performance may be impacted.
Ideally, you should schedule your session just before breaking your fast to take advantage of the anabolic window immediately after exercise.
Yes, women have increased sensitivity to kisspeptin , a molecule that regulates reproductive hormones.
Fasting that is too aggressive or too frequent can be perceived as a major stress by the female body and disrupt the menstrual cycle .
Women are often advised to practice a crescendo fast (12 to 14 hours at the beginning) and to avoid prolonged fasts during the week before their period.
Black coffee and plain tea (without sugar or milk) do not break the metabolic fast because they are calorie-free and do not raise insulin.
On the other hand, for stevia or sweeteners, the debate exists : although they are calorie-free, they can trigger a cephalic insulin response (your brain tastes the sugar and prepares insulin because it believes it is consuming it).
It's an ancestral survival mechanism. When food is scarce, your body remains in a state of alert so that you stay on the lookout to hunt and feed yourself.
If this happens to you, use breathing techniques or magnesium in the evening, and accept that your body is in temporary alert mode.
Even though fasting is powerful, it is not suitable for everyone all the time.
If you are pregnant, breastfeeding, have a history of eating disorders, or have a BMI below 18, I advise against fasting.
If you have any doubts or a specific medical condition, always ask your doctor for advice before starting.
The longer your fast, the more delicate your refeeding should be. If you eat too much at once, you risk digestive shock .
Start with bone broth or some cooked vegetables, then wait an hour before your real meal.
Above all, avoid gorging on carbohydrates (pasta, sugar) for your first meal, as your body will be hypersensitive to them.