Fasting: What is it and how does it work


Intermittent fasting is a voluntary shortening of the “eating window”, i.e. the time you eat, to 8 hours or less.

This does not mean you have to eat continuously for 8 hours. At this time, you eat as usual, and during fasting hours you abstain from food (all non-caloric beverages, including tea and coffee, are allowed).

There are several types of intermittent fasting. Most practical: 8/16 (8 hours – regular meals, 16 hours – fasting, including a night’s sleep), 4/20 and 36-hour fasting (night + day + night).

How does fasting work?

Our cells have a built-in mechanism for the utilization and treatment of failing organelles – autophagy. Improper or insufficient functioning of the autophagy system leads to premature aging and tissue breakdown. This effect is especially noticeable for nerve cells and cells of internal organs.

Autophagy can be stimulated by drugs and is now a promising area of ​​research. However, in the case of nervous tissue, the drug approach is hampered by the presence of a special barrier in the vessels of the brain and spinal cord, which prevents most substances from passing into the tissues.

At the same time, it has been shown for nervous tissue that intermittent fasting (lasting 24 to 48 hours) significantly increases the number of autolysosomes – organelles that make use of faulty cellular structures. Similar results were obtained for liver cells.

Thus, during intermittent starvation, cells are freed from the need to process incoming nutrients and can more actively use their own failing components, updating themselves and improving their work.

What do we get?

Bleeding decrease in insulin concentration glucose and insulin-like growth factor (a substance that accelerates aging and is a risk factor for the appearance of tumours).

Animal studies have shown that intermittent fasting reduces the likelihood of occurrence and slows the growth of neoplasms, including malignant ones. For humans, there is much less data, but there are also positive results.

More is released during intermittent fasting growth hormone which promotes fat burning and muscle gain.

Really, fat burning is one of the most researched effects of intermittent fasting. At the same time, weight loss occurs due to lower calorie intake – you skip one or two meals a day, and as a result, you lose weight. It is logical that the weight only decreases if there is no overeating on normal eating days. If you want to lose weight while maintaining muscle mass, it’s best to stick with periodic calorie reduction.

In overweight people and the elderly, they improve cognitive functions: verbal and visual memory; the amount of markers of Alzheimer’s disease in the cerebrospinal fluid decreases. Such results have been achieved with both intermittent fasting and a low-carb diet.

Number of inflammation markers and oxidative stress (free radicals).

Longer fasting periods (5-10 days) have been shown to promote lower blood pressure in hypertensive patients.

The most well-known effects that have made intermittent fasting so popular are metabolic. It increases the sensitivity of cells to insulin, lowers blood sugar and stimulates the breakdown of subcutaneous fat, especially the most dangerous – abdominal.

Moreover, positive changes in glucose and insulin metabolism have been observed even in people of normal build without concomitant weight loss. Thus, the risk of type 2 diabetes (non-insulin dependent) is reduced.

Finally, rodent studies have shown (e.g. here and here) that intermittent fasting and concomitant calorie reduction significantly increase life expectancy.

In fact, with similar studies, the popularity of intermittent fasting began. In humans, this effect has not yet been sufficiently studied – too little time has passed since the first publications.

But even if you don’t live one and a half times longer than the mice in the studies, your old age will certainly be much more pleasant thanks to all the above effects.

More and more details – in the analysis of the literature here.

How does this fit in with sports?

The effect of intermittent fasting on professional athletes has not been studied. But there are still studies on this subject. This is a study of religious fasting that comes as close as possible to “classic” intermittent fasting – Ramadan among Muslims.

Analyzing these studies, it appears that in most sports performance deteriorates during Ramadan. When studying the athletic activity of untrained men, the results were similar – agility, flexibility, aerobic and anaerobic endurance deteriorated.

However, these results cannot be fully transferred to traditional intermittent fasting due to the nature of Ramadan. During this time, it is forbidden to consume not only food, but also to drink during the day. Consequently, people tend to overeat early in the morning and in the evening, which disrupts the normal rhythm of sleep and wakefulness. And lack of fluid, especially during intense workouts, leads to dehydration.

At the same time, it is shown that with sufficient consumption of water and nutrients, even during Ramadan, it is possible to maintain sports performance at the same level.

On the other hand, renewing and increasing the number of mitochondria (organelles that produce energy substances for the cell) during intermittent fasting can increase endurance.

Exercising in a carbohydrate-deficient state (whether fasted or on a low-carb diet) also stimulates mitochondria formation. In this case, the volume of the muscles will not increase.

As a result, scientists come to the conclusion that a low carbohydrate and at the same time low calorie diet (or intermittent fasting) will help to reduce fat mass during endurance exercise, and to gain muscle mass, a diet high calorie with enough carbohydrates is necessary.

And also – that a low level of glycogen in the muscles may not worsen the results, but its high content during endurance exercises improves the results (unexpectedly, right?).

Another issue for exercisers is fitting the right amount of calories into a reduced eating window. It’s one thing if you sometimes run 5 km slowly and 1500-2000 kcal on intermittent fasting days is enough for you. They can easily be divided into three meals.

The situation is quite different for professional athletes who train for several hours a day. Their 4,000 to 5,000 calories cannot be easily squeezed into an eight hour window. And when you consider the recommended protein intake and the intervals of its intake, everything becomes quite complicated.

What is the result?

  • Intermittent fasting won’t help you lose weight if your calorie intake stays the same. If food calories are reduced through intermittent fasting, you are more likely to lose weight from fat rather than muscle.
  • During intermittent fasting, cellular self-repair processes are initiated that prevent type 2 diabetes, and metabolic syndrome, and help lower blood pressure. Some reduction in the risk of Alzheimer’s disease and neoplasms is also possible (comprehensive studies have only been conducted on animals).
  • For moderately trained people, it is quite realistic to include intermittent fasting in their lifestyle and get all of the described benefits.
  • With vigorous training (several hours a day), it can be difficult to get the required amount of nutrients during intermittent fasting.
  • Provided you receive a complete diet in terms of calories and nutrients, as well as adequate fluid intake, sports performance does not deteriorate even during periods of hunger.