Intermittent fasting consists of stopping food for certain periods of time. This is intended to lose weight but also maintain weight over time, a burning issue in which most conventional diets fail miserably. It is the famous "bounce" effect.
There is nothing stipulated about the duration of intermittent fasting. It can be as variable as being able to eat from 8 in the morning to 2 in the afternoon and fasting the rest of the day, such as not eating every other day or just one within a week. In the period of time in which eating is allowed, there is no limit on the number of meals to be made or the quantity. This seems attractive because with proper balance it is possible not to starve. It is enough to eat well or very well and then live on what has been accumulated.
Nothing further from reality. It is a diet or way of life, whatever you want to call it, just as harmful as other diets that at first glance seem much more dangerous. I explain the reasons.
The first is the absence of serious studies to certify its validity. Well, it's not entirely true. In 2019 an article was published in the journal Obesity with the promising title "Early time restricted feeding reduces appetite and increases fat oxidation, but does not affect energy expenditure in humans" signed by Eric Ravussin, Robbie A. Beyl , Eleonora Poggiogalle, Daniel S. Hsia, and Courtney M. Peterson.
According to these scientists, eating only from 8 in the morning to 2 in the afternoon allows you to lose weight, limits the appetite and does not affect the energy expenditure of the individual (which is more or less what the title says, except for the time period from 8am to 2 pm that is already indicated more in the article). Of course, the article is not supported by several verified scientific studies and therefore is considered a "minor" study. In any case, if you have to pay attention to a schedule, the only one with a certain scientific endorsement would be the one that allows you to eat from 8 to 14 hours and that was tested by this group of scientists. The rest of the schedules that you have heard out there come from gurus who have troubles to write their own name or from celebrities, tiktokers or youtubers who endorse whatever it is in order to gain subscribers.
The second reason has to do with the dangers of messing with blood glucose. In principle, hunger is activated when blood glucose falls. When our body needs nutrients, a neurotransmitter called "neuropeptide Y" is released, which is responsible for spreading an essential message through the brain: it is time to eat. The ghrelin hormone, commonly known as the hunger hormone, is found in the blood. When we are hungry, the amount of this hormone increases - mainly secreted by the stomach - and when we have finished eating, it decreases rapidly.
When we have the need to eat, the production of ghrelin is activated and the action of neuropetide Y is triggered. The brain, stimulated by this activity, generates the need to consume products that provide glucose, which is its main food. At night, when we sleep, our body continues to consume energy so ghrelin and the action of NPY are triggered again. This causes that when we wake up we are hungry and we need breakfast, a fundamental act of our daily diet that many ignore in a very wrong way.
In 1994, a new hormone called leptin was discovered. Leptin levels increase after eating food, favoring the action of anorexic peptides - those that inhibit hunger. It was also discovered that when adipocytes - cells that store fat - lose part of this fat, they lower the action of leptin, favoring the individual to eat food. In summary, that a "normal" individual before eating has high ghrelin and low leptin values and vice versa when he has eaten.
To further complicate things, there is another hormone, called CCK or cholecystokinin that is generated in the intestine and that affects the individual's appetite in a similar way to the previous ones: when we are full, it triggers the action of neuronal transmitters that tell the brain that we are satiated. This hormone is being studied in depth because there is a possibility that it is related to various eating disorders. Thus, those who suffer from bulimia - rapid and massive food intake - would have low levels of CCK - while anorexics - inability to eat, immediate feeling of satiety - would generate large amounts of CCK with just the ingestion of a few tablespoons of food.
It is also believed that the generation of CCK can be affected by the mood of the individual and that would explain why depression causes anorexia (or perhaps anorexia is a form of depression, who knows).
So ghrelin, leptin, CCK and serotonin (a neurotransmitter also involved in sleep, sexuality, temperament ...) play an important role in hunger. All this, which sounds very complicated, is usually simplified by saying that we are hungry because blood glucose falls. This activates the need to eat and as soon as we can put something in our mouth, the hormone insulin is secreted, which alerts the cells of the body to receive the ingested nutrients.
If insulin and blood glucose sound like diabetes, you are right. At the University of Sao Paulo in Brazil they studied the effect of intermittent fasting in rats and discovered damage to the cells of the pancreas responsible for generating insulin. These damages, mainly the presence of free radicals and insulin resistance, can cause healthy people to get type II diabetes.
Glucose reaches all parts of our body. It is for this reason that individuals affected by diabetes can present multiple symptoms since problems with insulin affect the entire body. Beware with diabetes, which kills more and in a more subtle way - because it seems a mild disease when it is not - than covid or cancer.
When we do not consume carbohydrates - the main source of glucose - chemical compounds called ketone bodies are generated because the pancreas releases another hormone, glucagon, whose mission is to transform fat into glycogen. Ketone bodies would be responsible for supplying energy when food is lacking.
In the absence of glucose, the body pulls the energy reserves accumulated in fat, which translates into a decrease in it. This seems positive, but it just seems so.
We are telling the body that it has entered a phase of deprivation, of lack of food and it reacts in a "conservative" way, adapting to the lack of food, minimizing metabolic expenditure. After a while intermittent fasting will do little good. What's more, you will even gain weight. If there is a reaction of the individual intensifying the fast since he thinks that he is doing it "wrong", the process can have severe consequences for its health.
Since there are no limitations on the food that can be consumed in the "allowed" hours, binge eating can be frequent but there are also people who continue to strictly control what they eat with what fasting actually extends beyond what which has been randomly chosen as the schedule for it.
There's still more. Intermittent fasting, like other types of poorly focused diets and without any scientific-medical endorsement, can cause serious eating disorders. One of the most common caused by this type of diet is orthorexia, which is defined as the pathological obsession to eat healthy. The individual who suffers from it can present severe nutritional deficiencies without being aware of it since he thinks that he actually eats healthy. Intermittent fasting makes him even more inflexible, leading to socialization problems. He is the type of person who does not go out to dinner with friends if it coincides with his fasting schedule, avoids going to eat at his parents' house because he thinks that they do not eat healthy there, or eagerly searches the Internet for ingredients and recipes that suit his dietary beliefs, not caring if what they express makes any logical and reasonable sense.
Another of the negative effects of intermittent fasting occurs in the alteration of the REM sleep cycle, decreasing its duration, which causes mood swings in the individual, as well as the ability to learn and concentrate.
The initial effects of maximum concentration and mental agility that occur when starting an intermittent fasting are due precisely to starvation and have been perfectly studied in people who have gone on hunger strikes for various reasons. Over time this situation turns into fatigue, dizziness and lack of will to undertake tasks.
Another effect of intermittent fasting is the increase in the production of cortisol, a hormone that is associated with high levels of stress since the body generates it as a reaction to it but also to the low presence of glucocorticoids in the blood. If a hormone begins its name with "gluco ..." you can already imagine what it is associated with, right?
Intermittent fasting has been associated with hair loss and a lack of regularity of the period, as well as the feeling of guilt that is generated when the established schedule is not strictly followed in addition to irritability. And a mental problem is as serious as a physical one, make no mistake about it.
After reading this, do you still think that intermittent fasting is of any use?
The truth is, except for half-enlightened gurus, no doctor, nutritionist, or endocrine would recommend such a diet.
