I'm sure you've already seen and listened to posts from various pseudoscientific bloggers about the benefits of intermittent fasting. They all spin a tirade about some mythical (to them) autophagy that occurs during fasting and rejuvenates the body. Moreover, scientists and doctors alike propagate this tirade, claiming it's safe and should be done... However, this is absolutely not true.
Let's explore together what happens to a healthy body during fasting and what happens to an unhealthy one. There are two main types of intermittent fasting: alternate-day fasting and time-restricted fasting. In the first type, people alternate days when they eat very few calories and days when they eat whatever they want. In the second type, they are allowed to eat whatever they want for a certain period of time (4 to 10 hours a day), and abstain from food the rest of the time. For example, let's first take a healthy person who begins fasting using either type. As long as they are overweight, this process will be beneficial. Growth hormone increases, which triggers enzymes that, in turn, begin to break down adipocytes (fat cells) into fatty acids, which in turn enter the bloodstream, where they are absorbed by other cells to create ATP. This is adenosine triphosphate, or adenosine triphosphate. It is a universal energy source for all biochemical processes. Something like gasoline for cells.
As long as there's a calorie deficit and fat, the body burns this fat for ATP, and the cells are happy. However, problems arise when the fat runs out: When ATP is depleted, our cells begin to realize they're "on the sap." AMPK helps them with this . This is AMP-activated protein kinase, a cellular protein kinase that controls the cell's energy balance. It is activated when intracellular AMP levels rise. This is adenosine monophosphate, a product of ATP metabolism. So, roughly speaking, when AMP levels are high, this molecular switch (AMPK) understands that the cell is running low on "gasoline," and it needs to give commands: conserve energy, stop dividing, trigger autophagy , etc.
By the way, for those who don't know what autophagy is , it's cannibalism. Yes, it's bad for humans, but cells operate by different laws. If cells experience a severe ATP deficiency, they consume their own organelles and the remains of nearby dead cells. Is this good? To a certain extent, it's good; it's something like natural selection in a concentration camp. For those who don't understand the analogy, only initially healthy people survived. Sick people died and were removed from the barracks to prevent infections. So it is here, too: supposedly weak cells die, while stronger cells "eat" their remains or simply get rid of them.
In addition to autophagy and fat burning, the body begins to obtain energy (ATP) from glycogen (glucose stores in muscles) and then from muscle proteins. This means it begins to break down muscle into peptides using various enzymes to obtain amino acids for gluconeogenesis . This is a metabolic pathway that results in the formation of glucose from non-carbohydrate compounds. As a result, a person loses weight, or in other words, gets rid of some of their tissue, primarily fat and muscle.
Is this good? For a fat person, it might be beneficial (in part). But what happens to a thin person? There's no fat, little muscle. And no calories. Cells need to survive somehow. The minimal fat that's present goes to the firebox, then the minimal muscle, and then cartilage, skin, ligaments ... Is this good? Not at all. These are essentially degenerative changes in the body .
What happens if a person also has a growth hormone deficiency, as I mentioned above? This creates a truly tragic situation: the remaining fat can't be burned effectively, because without growth hormone, lipolysis occurs through other hormones, and less effectively. The person's immune system suffers, wrinkles appear, thyroid and gonad activity decreases, and so on. As a result, they can easily contract infections, develop cancer, and so on.
So, what's the bottom line? Fasting is only appropriate for obese, healthy people (assuming they're obese) . Fat will be lost, but at the same time, the person won't be getting the necessary vitamins and minerals from food, which isn't good in the long term. We need to change our approaches; fasting isn't the only way to lose fat. Unhealthy people, especially those with liver problems or growth hormone deficiency, should absolutely not fast! Fasting will only worsen energy and protein deficiencies, which makes the body vulnerable (primarily to infection).
Here's a video of autophagy occurring inside mouse cancer cells. You can see the cell eating itself from the inside out:
For those interested in all the mechanisms of cell survival and death, I recommend this lecture:
