What Is Intermittent Fasting?
Intermittent Fasting (IF) is a type of eating that has recently gained a lot of popularity.
Today, three intermittent fasting regimens are the most widely studied:
- Time-limited food intake: 8 h / 16 h (this means 8 h-meal time and 16 h-fast) – this intermittent fasting mode is displayed in the visual material of the recording;
- Fasting 5:2. Five days are normally eaten and two days are fasted every week;
- One day a week with significantly reduced calories (eg 500 – 700 kcal / d)
In the fasted state, we arrive 8-12 hours (or more) after the last meal and it is determined by whether we get the nutrients and energy from external resources (the food we have ingested) or move to internal resources.
- 0h – we eat.
- 0-6h after a meal – digestion takes place.
- 6-8h – after digestive condition (postabsorptive), we have available nutrients from the last meal eaten.
- 8-12h – the body enters a state of fasting, begins to use internal resources. It is believed that this transition from external to internal resources is what causes potentially valuable biochemical processes in the body.
- 12-48h – glycogen, glycerin, fats and ketones are used as fuel.
- 48-72h – the body’s processes slow down.
- 72 + h – the body begins to use body fat as the only fuel.
In long-term fasting, this shift in fuel from carbohydrates to fat is what protects our protein stores (proteins make up all of our internal structures). Therefore, the loss of muscle mass occurs in a much later fasting phase, not immediately.
During fasting, after several days, there are changes in the fatty acids in the bloodstream – from the predominantly saturated fatty acids, the proportion of unsaturated fatty acids in the blood increases over time.
The content of these fatty acids in the blood is what is associated with longevity.
What are the Benefits of Intermittent Fasting?
Some studies show that this diet can improve health by reducing obesity and overweight, reducing the risk of various chronic diseases (diabetes, cardiovascular disease, cancer, etc.), and improving thinking skills.
Obesity And Diabetes
Animal studies have shown that interrupted fasting improves insulin sensitivity, prevents obesity, which is mainly caused by a high-fat diet, and improves the manifestations of diabetic retinopathy.
On the island of Okinawa, people traditionally follow a fasting diet, so they have low rates of obesity and diabetes, and a particularly long survival.
The inhabitants of this island eat a nutrient-rich, low-calorie diet. They eat a lot of sweet potatoes, other vegetables and legumes.
Six short-term studies in overweight and obese adults concluded that starvation was more effective in reducing weight than known standard diets.
The results of two studies carried out in 2018 showed that reducing daily calories or fasting for 24 hours three times a week improved insulin resistance in patients with prediabetes or type 2 diabetes.
In contrast, in 2017, a 12-month study was conducted comparing daily intake, daily calorie reduction, and control diet.
Participants in both groups of altered diets lost weight, but did not experience improvement in insulin sensitivity, lipid metabolism, arterial blood pressure compared to control diet participants.
Several studies are available showing that interruption of fasting in both animals and humans improves markers of cardiovascular disease, including
- arterial blood pressure;
- resting heart rate;
- high and low-density lipoproteins;
- and insulin resistance.
We have also found an association with inhibition of atherosclerosis.
The CALERIE (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy) study found that reducing calorie intake by 12% reduced several risk factors for cardiovascular disease in non-obese individuals over two years.
We usually see improvements in cardiovascular indicators within 2 to 4 weeks after the start of interrupted fasting, and this effect disappears within a few weeks of returning to a normal diet.
Animal studies performed about 100 years ago have shown that fasting may be effective in the treatment of oncological diseases.
Since then, several studies in rodents have shown that reduced caloric intake reduces the development of oncological diseases during the normal aging process, and improves the sensitivity of an existing oncological process to chemotherapy and radiation therapy.
There are currently some clinical trials in oncology patients, and most of the studies already focused on the tolerability of discontinued fasting, side effects and biomarker characteristics.
For example, a study of calorie reduction in patients with prostate cancer found that patients were well tolerated (95%) and did not show any adverse events.
Several case studies involving patients with glioblastoma have shown that interrupted fasting can reduce growth and prolong survival.
Patients with breast, ovarian, prostate, endometrial, colorectal and glioblastoma are currently being actively studied. To date, there is no evidence that interrupted fasting could affect the development of the oncological process in humans.
Several epidemiological studies suggest that excessive caloric intake, especially in middle age, exacerbates the development of stroke, Alzheimer’s and Parkinson’s disease.
At present, it is not possible to get sufficient data from controlled studies on the use of intermittent fasting in patients at risk for, or with a history of, neurodegenerative diseases.
We should start such studies in the early stages of the disease and should last long enough to detect the onset of disease-causing effects.
Weight loss reduces the symptoms of bronchial asthma in overweight patients. In a 2007 study, they gave patients with bronchial asthma a daily diet. Within two months, they lost weight and had symptoms of bronchial asthma.
It is an autoimmune disease characterized by axonal demyelination and neuronal degeneration. In mice with experimentally induced autoimmune encephalomyelitis, a daily diet reduces autoimmune demyelination.
Two recent pilot studies showed that patients with multiple sclerosis who followed a starvation regimen had a reduction in symptoms within two months.
Given that interrupted fasting reduces inflammatory processes, it could also have a positive effect in patients with rheumatoid arthritis, but only data on arthritis are currently available, and they have conducted the study for a relatively long time.
Surgical and Ischemic Tissue Damage
In animals, interrupted fasting reduces tissue damage and improves the recovery of traumatic and ischemic damage. Fasting before surgery reduces tissue damage and inflammation.
A randomized, multicenter study found that reducing daily caloric intake over two weeks improved outcomes after gastric bypass surgery. Such data suggest that preoperatively controlled intermittent fasting could be a safe and effective method to improve surgical performance.
Some animal studies have concluded that intermittent fasting is effective in traumatic head or spine injuries. Following discontinuation of fasting, rats showed an improvement in functional capacity after injury to the neck or thorax of the spine.
Evidence from a growing body of research suggests that interrupted fasting can improve athletes’ performance and can be seen as a practical approach to improving the course of the disease in athletes with traumatic brain or spinal cord injuries.
Animal studies suggest that interrupted fasting may protect against ischemic injury to the brain, liver and kidneys, but there is no doubt that the potential therapeutic effects of this regimen on stroke and myocardial infarction should be further investigated.
In conclusion, both preclinical and clinical studies suggest that interval fasting can have several positive effects on several diseases, including obesity, diabetes, cardiovascular, oncological and neurological diseases.
Animal studies show that interval fasting prolongs survival, although clinical trials to date have been limited to a few months, so we have not established it whether humans can continue this diet over a long period of years and achieve the same improvements as animals.
Clinical trials to date have mainly included young or middle-aged overweight patients, so it is not appropriate to extend these data to other patient groups. In addition, we have not fully explained the mechanisms by which interval fasting affects metabolic processes.
Understanding this, it would be possible to create a targeted pharmacological therapy that would resemble an intermittent fasting regimen without the need to change eating habits.
Studies analyzing the mechanisms of calorie reduction and fasting in animals have resulted in the development and testing of pharmacological agents that can mimic the effects of a particular food intake.
An example is metformin. There are other drugs that have been studied less, but data from animal studies suggest that the safety and efficacy of such drugs are unlikely to outweigh the discontinued fasting regimen.
Benefits of Intermittent Fasting
- Reduces body fat mass and weight.
- Promotes the acceleration of metabolism.
- Reduces blood sugar and insulin levels.
- Increases the secretion of growth hormone, which promotes fat burning and muscle gain.
- Relatively convenient method that can be easily adapted to your individual mode.
- We need to spend less on food, we can use the money we save to buy more expensive but high-quality raw materials for a meal.
- Improves brain function and, according to recent studies, delays the onset of Parkinson’s, Alzheimer’s and dementia symptoms.
The Bottom Line
It is important to understand that this diet is not a “super-diet” that will help you lose all your excess weight and never get sick.
As this eating regime only limits the time of eating, but does not require any restrictions on the choice of food, the results are directly up to you.
Weight loss with this diet is most often the result of consuming fewer calories than before. If you follow the first of the above fasting regimens for weight loss, do not try to “squeeze” all your meals in this 8-hour window, but refuse a meal – breakfast or dinner.
Also, if you follow the 2nd or 3rd of the fasting regimens, beware of unintentional “calorie compensation” on non-fasting days. On days when you are not hungry, try to eat healthy and balanced.
It is important to consult with specialists in the relevant field within these eating restrictions, who would provide individual and relevant information, independent communication, support, and regular monitoring of dynamics.
Is Interval Intermittent Fasting Right For Me?
Intermittent fasting or periodic calorie restriction can help improve metabolic problems such as high blood sugar and lipids (cholesterol and triglycerides) and reduce inflammation.
It can help you lose weight / fat mass as it helps us absorb less energy.
If you feel that skipping breakfast makes you overeat in the evenings, then you need to think about whether this is the best approach.
Maybe it’s better to eat a protein-rich breakfast when you’re hungry, and an excellent lunch and dinner, and not look in the fridge so often late at night.
Returning to periodic fasting, we also attribute it to the ability to improve brain and heart health, reduce the risk of tumors, stimulate cell regeneration, etc.
We must understand it that this is not magic formula. It’s just one method. It is also not much better than regular calorie restriction.
It is not clearly good, bad or neutral. We never know what effect a particular stimulus will have on our body at the moment.
Therefore, not all the benefits listed may be felt by everyone. In studies, the average is “pulled out”, respectively, for one the reaction is strong, for another it is practically non-existent.
Basically, the sicker a person is (with bigger metabolic problems), the more pronounced they felt some improvement. A healthy person may not experience any effect from periodic fasting.
Remember that sports and simple calorie restriction will bring very similar health benefits.
Interval Intermittent Fasting for Slimming
To lose extra pounds / fat, you need to create a calorie deficit.
This usually means that people follow a diet or eating less. As you know, there is nothing fun about it, because hunger and self-indulgence are your allies ALL the time.
Therefore, basic skills such as eating slowly add up to 80% satiety, and including protein and vegetables in every meal, are fundamental and make it much easier to reduce the amount of food eaten.
However, maintaining a stable calorie deficit is difficult, so a technique such as interval fasting can be valuable.
This means that during eating periods a person eats as usual, but at other times does not eat at all or eats minimally.
Studies show that periodic energy restriction (or minimal eating instead of complete fasting) is even more successful than periodic fasting in the classical form.
This can take the form of, for example, eating 4 days a week as usual, and the remaining 3 days around 25% of your usual calorie ‘budget’. In this way, we can create a stable calorie deficit on a weekly basis.
However, we must remember that fasting or periodic energy limitation alone will not guarantee long-term, permanent weight loss.
Interval Intermittent Fasting May Reduce Metabolic Adaptation
By prolonged restriction of caloric intake, the metabolism adjusts and becomes slower. This article details that. But in theory, if we consume fewer calories at intervals, these processes do not become so pronounced.
The reality is very different. Someone loses excess pounds relatively easily and feels good. Others feel “bloated” and with “saccharified” hormones.
Probably the key to success lies in not limiting your energy intake for too long and too hard.
Interval fasting is not a panacea and should not be seen as an end in itself.
It is only one way to improve health and feel better, but only if it is adapted to each person’s individual circumstances.
What to consider when someone tells you that intermittent fasting is the elixir of eternal youth and a miracle cure for slimming?
Look at this person with skepticism.
Here are some things to think about.
First of all, nutrition science is new in itself (in diapers, you could say), we still have more questions than answers on many topics, including interval fasting.
So no one yet knows everything about 100%. It is difficult to carry out qualitative research on people, because rarely anyone agrees to be in the laboratory for a long time and fast. And rarely does a large organization want to pay for such research.
Second, humans are not animals. Many studies have been performed in rats, but it is difficult to guarantee exactly the same results in humans.
Third, not all people are created equal.
For example, the reactions of men to fasting are different from the reactions of women.
Evolution has made a woman’s body “safer” to produce offspring, which means that:
- Women have a genetically higher fat mass than men;
- Women find it harder to lose weight than men;
- Women’s hunger hormones will “break out” in conditions of more limited energy, which means that we will be more hungry, we will feel the urge to overeat when we can “eat” again, and we will feel the pull of sweet and fatty products.
There will also be a different response to periodic fasting in humans:
- At different ages;
- With different levels of activity;
- With different metabolic health – people without metabolic disorders may not feel the effects of periodic fasting;
- With different body weight;
- With a different circadian rhythm – people who take the energy of the day mostly in the morning may have a different body composition and metabolic state than people who take the energy in the evening, although the amount of energy will be the same.
As you can see, this is a very complex issue and even in large meta-analyzes (where data from many studies are analyzed) there is no clear answer about the effects of fasting – it differs from both climate and circadian rhythms, common menus and traditions.
Also, research and experimentation are not real life. It makes a difference whether there is a drastic fast in the laboratory or every now and then in real life, because “it happened”.
It makes a difference whether it is followed for 5 weeks or 5 years. There is a difference in how we eat eating “windows”.
The most important thing to consider is that all the benefits we see from interval fasting probably come from calorie restriction and from losing excess weight.
People who lose excess fat improve all health parameters. Fat cells are not only a storehouse of excess energy, they also cause an unwanted metabolic environment in the body, increasing inflammation and reducing insulin sensitivity.
Excess weight also puts extra strain on the joints and heart. Therefore, the very fact that we lose excess fat mass has a huge positive effect on all processes in the body and it is not 100% clear whether they are caused by fasting or fat loss.
In a study of patients with type 2 diabetes, comparing interval fasting (eating ‘windows’) with normal calorie restriction and fasting every other day, no differences were found between the three methods:
all helped reduce excess weight. How much was lost depended on the total amount of calories ingested;
all reduced blood glucose levels;
and all improved insulin sensitivity, most often in direct proportion to weight loss.
Weight loss can be achieved by any method.
Although some studies have shown that it is easier for people to stick to interval fasting. In other studies, this was not confirmed…
It all depends on whether a person does not overeat during the periods in which he eats.
People who overeated or compensated for the lack of energy very often did not lose weight and, even if they did, their overall metabolic health did not improve.
This only means again that fasting at intervals alone is not a panacea, and if a person’s overall eating habits are low, he simply “pushes” them in a shorter period of time.
Interval Intermittent Fasting and Female Body
At the moment, the picture looks like this: there are a lot of women who say that fasting at intervals is the best thing that has happened to them since the invention of grapefruit.
While others complain of serious problems such as uncontrolled overeating, hormonal problems, menstruation and even premature menopause).
This is because the female reproductive system is very sensitive to energy restriction. Here, of course, the individual peculiarities of the organism and the coincidence of other circumstances are also manifested.
In both men and women, the hypothalamic-pituitary-gonadal (HPG) axis – a collaboration of three endocrine glands – acts almost as an air traffic controller.
First, gonadotropin-releasing hormone (Gn-RH) is released in the hypothalamus.
This causes the pituitary gland to release luteinising hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH then act on the gonads (testicles or ovaries).
In women, it causes the production of estrogen and progesterone, which we need to release a mature egg (ovulation) and support pregnancy.
In men, it causes testosterone and sperm production.
Because this chain of reactions occurs in women in a very specific, regular cycle, the Gn-RH pulses must arrive at a very precise time or everything may go “crosswise”.
Gn-RH impulses appear to be very sensitive to environmental factors and can be disrupted even by innocent activities such as a more drastic diet or fasting.
Even a short fast (say, three days) changes the hormonal rhythm in some women.
There is even the phenomenon that skipping a single meal (which is not completely extreme in itself) can lead to anxiety, so that the body is ready to take appropriate action if the energy restriction continues.
In terms of research results, there are generally few qualitative long-term studies on the effects of periodic fasting on male and female bodies and weight loss. But those who do point to:
Glucose tolerance in men improves but deteriorates in women. Therefore, women with type 2 diabetes should avoid periodic fasting as it may worsen the condition.
Another study found that fasting for 2 days increased the activity of the sympathetic nervous system in women (fighting or running away), but we saw no such response in men. Stress levels will also vary depending on a woman’s overall stress level.
PCOS (polycystic ovary syndrome) improved with fasting.
There are no qualitative studies on the effects of fasting on women. There is a study on its effects in rats. And that’s not gratifying. Even after fasting for 10-15 days every other day, there was a total chaos in female sex hormones and metabolic hormones.
Therefore, if you are a woman, be careful with fasting. Watch yourself and your body. A serious signal is the lack of menstruation.
And while you may not want to get pregnant right now, know that they closely relate metabolic hormones to sex hormones. If the latter is a problem, know that there is also a mess in the metabolism in the kitchen. And that’s nothing good.
Interestingly, this is mainly because of a lack of protein. Women consume less protein than men, but fasting further reduces protein levels. What does it mean?
We need the amino acids that make up proteins to stimulate the hormone estrogen receptors, and to release IGF-1. IGF-1 starts uterine wall thickening. If this process is disrupted, it disrupts the reproductive cycle (so low protein intake can delay pregnancy).
Fluctuations in estrogen levels do not stop at sex problems. It even affects cognitive function, digestion, appetite, mood, protein synthesis, bone formation, etc.
But evolution has thought of everything. A woman must have a reserve of energy and have mechanisms that prevent it from losing it so easily.
Also, nature will not allow you to get pregnant if you feel that we do not supply the body with the necessary energy. Therefore, the reproductive system works hand in hand with metabolism.
Females of virtually all other species can end a pregnancy if adverse conditions occur. Man cannot do that. Therefore, a woman’s body must function in such a way that the woman can carry the baby to there or what.
Returning to interval fasting, stop it as soon as I get the following signs:
- Menstruation disappears or remains irregular;
- You have trouble sleeping
- You start to lose hair;
- Your skin becomes dry and a rash appears;
- You cannot recover so easily after exercise;
- Wounds heal more slowly and you catch the first virus that wanders in a circle;
- Your stress tolerance decreases;
- You get mood swings;
- Your libido is gone to rest;
- Your digestion has slowed down;
- You have a cold all the time.
We should understand it that not all women have problems with periodic fasting or any other calorie restriction. You just have to be careful and watch yourself.
What Types of Intermittent Fasting are There?
The first way to start is to skip a meal sometimes (a couple of times a week).
The next level is a “trial” fast – 24 hours without food for the first time in your life – to get to know your feelings, to get to know hunger, to understand that you will survive without food.
Regular fasting 24 hours, eg once a week, once a month, etc. Should not be taken more than twice a week.
Time restricted feeding – sometimes called the 5: 2 protocol. A couple of times a week eats minimally (10-25% of the usual amount of calories). The other days eat as usual.
Relatively the strictest, but also the most popular method, is fasting at daily intervals with a “window” of eating and a “window” of non-eating. Usually 16h eating and 8h eating are used, but we can vary it.
Women might want a ‘softer’ approach, such as not eating for 14 hours and eating for 10 hours, or a less strict schedule in general.
We achieve the fasting effect after about 12 hours of ingestion.
People who want to improve their physical shape can also adapt this approach (ideally combined with strength training).
Here, you should eat a lot of protein and vegetables every day during meal periods.
We perform intensive strength training 3-4 times a week “on an empty stomach”, just before the first meal. We recommend it to use the essential amino acid food supplement (EAA) before training.
On training days, we supplement the menu with carbohydrates (rice, potatoes, bread, fruit, etc.)
The richest meal should be immediately after training.
Fasting diet – for a longer period of time (eg 3-7 days) energy intake is limited (about 50% of normal calories), followed by 3-4 weeks with normal eating.
36h fasting / 12h eating – or eating every other day.
Warriors diet or 20h not eating / 4h eating every day.
As you can see, there are many opportunities. Smart and careful experimentation is the best way to understand if interval fasting is right for you and which type will be yours.
How Do I Apply Intermittent Fasting Diet in My Daily Routine?
It all depends on the purpose. To get all the benefits of fasting, in the classic approach, only liquid (without calories) is used in the “windows” of fasting – water, tea, black coffee.
We believe it that coffee with milk or cream or so on, bulletproof coffee (with butter or coconut oil) is also acceptable.
However, as I have already written, it can be approached more liberally and also benefit from the process, even if not all the protocols are followed so strictly.
If you cannot give up coffee with milk in the morning, but can do without breakfast, it is already a benefit if you allow to reduce the amount of food consumed per day.
Therefore, it all depends on the purpose. An ordinary person may be more interested in simply losing a few extra pounds than in providing daily autophagy and fighting for longevity.
Who is not Suitable For Intermittent Fasting?
- People with eating disorders (including in the past) and predisposition to them;
- Pregnant women and breastfeeding mothers (and women who currently want to conceive would not be desirable);
- For children, young people and the elderly;
- For people who do frequent and intense sports;
- For people who constantly need energy – hard workers;
- People with high overall stress levels (physical and psychological);
- Patients with type 1 diabetes (patients with type 2 diabetes should also exercise caution and consult a doctor before carrying out any experiments);
- For people who need to eat regularly to take medication.
I have already mentioned the risk factors for women.
The emotional background and our beliefs also influence whether fasting at intervals will be a successful and appropriate solution for the individual.
At a psychological level, interval fasting will not be as appropriate for people who:
- Considers it healthy to have regular meals;
- “Fears” hunger or considers it “dangerous”;
- Feel confined or “separated” from the windows of eating;
- Feel bad when others eat, but they do not;
- Worried about having to skip a scheduled meal.
The Bottom Line
A good diet or nutrition plan gives us the right amount of energy to achieve our goals (loss / maintenance of fat mass or gain / maintain muscle mass, athletic goals, etc.) and our individual needs.
Any “diet” or “program” should be based on vegetables, adequate protein, slow eating, a minimum amount of processed products, physical activity (because only during physical activity the body “properly” uses and “manages” the energy and nutrients obtained is, you can also add periodic fasts as another excellent tool.