Does Intermittent Fasting Work? All You Need to Know

Intermittent Fasting

Talks about intermittent fasting and its effects on health did not begin yesterday. Hippocrates wrote about the benefits of temporary abstinence from food, and modern experts – nutritionists and endocrinologists – do not deny the effect of it. But does intermittent fasting work?

It is worth clarifying that we are not talking about long-term curative fasting, which, by the way, has contraindications. In fact, many of us, without knowing it, sometimes resort to intermittent fasting. For example, when in the morning, we run away from home, not having time to eat breakfast. But first things first.

The main theme of the material is to show that intermittent fasting, in terms of using it for weight loss (fat burning), has no advantages over conventional calorie restriction.

Intermittent fasting is a handy tool for controlling hunger on a diet, but it is not a unique and super effective method for fat burning and maintaining muscle mass.

What is Intermittent Fasting?

Does Intermittent Fasting Work

To begin with, the intermittent fasting definition (or “alternate day fasting”) includes different variations of this dietary intake.

However, they all work according to a similar scheme – the day is divided into two so-called windows:

  1. Stage one, you do not eat for a certain period (~ 12-48 hours).
  2. Stage two (which follows the first), you eat for a certain period (~ 8-24 hours). It is during this period that you eat your daily calories based on your goals (weight loss/maintenance / bulking).

The duration of the windows is different – 12/12, 10/14, 1/23, but the most common option is 8/16, in which you can eat for 8 hours a day, while the remaining 16 have a period of “hungry” window.

This option is considered optimal in terms of the ratio of efficiency and comfort. In order to adhere to it, it is enough to refuse, for example, from late dinner and early breakfast – then most of the fasting period will fall on sleep, and meals can be distributed throughout the day without special restrictions.

What for?

intermittent fasting before and after

Let’s move on to the main thing – what is it for. Here we’ll talk about the so-called “Intermittent Fasting Benefits.”

Be fit

First, to maintain good physical shape. When switching to a hungry mode, the body starts the process of breaking down fat instead of glucose – this natural mechanism allowed our ancestors to survive in the absence of food, and modern man to get rid of the consequences of overeating.


Secondly, even with a relatively short period of starvation, the process of autophagy is intensified – getting rid of outdated cells and their particles. In combination with the increased production of growth hormone (this occurs especially actively during sleep), which is also ranked among the effects of fasting, this provides a powerful stimulus for cell renewal.

Blood sugar levels

Thirdly, intermittent fasting has an extremely positive effect on blood sugar levels – this is especially true for those with high blood sugar, including those with type II diabetes (you cannot starve yourself with insulin-dependent diabetes!).


The level of insulin is also normalized, as well as the sensitivity of cells to it, and to leptin, a hormone responsible for regulating appetite and signals of hunger or satiety is restored.

Resistance (decreased sensitivity to these two hormones) is a sign of metabolic syndrome – metabolic disorders that lead to various health problems, and also contributes to the rapid gain of visceral fat.

Unlike subcutaneous fat, it is deposited on the internal organs in the abdomen and increases the risk of cardiovascular and endocrinological diseases. Getting rid of visceral fat with a regular diet is quite difficult. Intermittent fasting on a regular basis attacks it quite successfully.

Digestive problems

Fourth, for those who suffer from digestive problems due to lazy intestinal motility or an unhealthy microbiome in it, fasting can help significantly improve the situation.

During fasting, inflammatory processes subside (and this, by the way, applies not only to the digestive system) and fermentation processes. Some experts argue that this is the ideal time to take probiotics in order to achieve maximum effect in the shortest possible time.


In addition, intermittent fasting is considered a good tool for normalizing blood pressure, lowering the level of “bad” cholesterol in the blood (called low-density lipoprotein), improving cognitive abilities, and even increasing the effect of chemotherapy.

Adherents of intermittent fasting claim that thanks to it, they feel lighter and more cheerful, it is easier for them to concentrate on work and important things, it is easier for them to endure stressful situations, it is easier to fall asleep in the evening, and wake up in the morning.

Intermittent Fasting Rules

best intermittent fasting app

So how to make intermittent fasting work?

Let’s take the very best option that people stop at most often and with which, most likely, it will be easy and quite comfortable to start – 8/16.

It would be logical to leave the period of the hungry window for the night because, without any effort, it will turn out to be hungry for 7-8 hours.

Let’s say you had dinner at 8 pm the night before, which means your next meal will be at 12 pm the next day.

In the evening, you can drink as much water and tea as you like without sugar, and in the morning, for example, start with coffee, but also without sugar and milk – it affects blood sugar levels and provokes the release of insulin.

If black coffee is not an option for you, it is better to add a little of the highest cream or replace it with green tea.

If your favorite meal is breakfast, just slide the food window early; for example, end it with an early dinner at 18:00. Some “starving” people refuse to eat at all.

Unlike medical fasting, intermittent fasting does not require a special exit – in those hours during which meals fall. You can eat what you want.

To enhance its effect, it is better to choose a complete diet of varied, whole, and natural foods, rather than running happily for the nearest fast food.

Regular exercise, even if it is moderate, will not harm either – the same 10 thousand steps a day, in addition to intermittent fasting, can affect the normalization of metabolism and stabilization or even weight loss.

Does Intermittent Fasting Work? Science, Studies, Evidence

intermittent fasting 5/2

After studying the theory of the intermittent fasting work, let’s proceed to real-life facts.

Seimon RV et al. Systematic Review

In December 2015, another systematic review was released, which summarized the available data on the presence/absence of physiological benefits for weight loss of diets with intermittent fasting (IF) over diets without IF (non-IF).

Of the 40 studies that were eligible for inclusion in the review (from the original, about 400+ sources), 12 studies were studied to compare the effects of diets with and without IF, on BMI, waist circumference, hips, and the ratio of waist to hip circumference.

And from other selected studies, for comparison, data were also obtained on the state of affairs on IF and without IF, with regards to:

  • insulin sensitivity,
  • blood glucose control,
  • thyroid hormone levels,
  • cortisol,
  • sex hormones.

In fact, the conclusions of the scientists do not differ much from what is already known at the moment, and in general, it was found that the available data allow us to say that diets with either IF or without IF lead “apparently to equivalent results » in terms of weight loss, changes in body composition;

These types of diets do not show any significant differences in both the improvement of insulin sensitivity and control of blood glucose levels, and the levels of thyroid hormones, cortisol, and sex hormones.


One fairly well-known advantage was highlighted in IFs over non-IF diets – improved management of hunger during the fasting phase.

Scientists hypothesize that increased ketone production during the fasting phase plays a role, although this effect itself is generally insignificant in order to have any crucial effect on improvements in body composition or greater weight loss (compared to non-IF diets).

Many adherents of alternate day fasting, who use this dietary intake in combination with athletic training, try to appeal to the fact that it is IF that allows them to achieve the effect of fat burning in the hunger phase (fasting phase) and gain muscle mass after the necessary nutrients begin to enter their bodies with food.

That is, according to the idea of ​​the IF, according to their statements, it should help them to realize the so-called “clean bulking.”

Or, if IF is used in combination with strength training on a low-calorie diet, then such manipulation allows them to “burn” more fat and preserve muscle mass more (due to the presence in the strength training regime, which allows you to optimize the issue of maintaining muscle mass on a diet).

The study by Grant M Tinsley et al.

In September 2015, at the 12th ISSN (International Society of Sports Nutrition) conference, Grant Tinsley presented a report.

It was announced that Tinsley and a group of scientists conducted a study in which they compared the effects of a combination of strength training ( 3 days a week) with either an IF diet (4-hour food window on non-training days) or a non-IF diet.

The subjects were measured for body composition (DXA method); tested 1RM and muscle endurance in the bench press and leg press.

According to the scientists, the dietary protocol with IF in combination with strength training, for 8 weeks, did not show any changes in improving body composition.

Both groups of subjects managed to maintain muscle mass, but at the same time, despite the diet with IF, IFs did not manage to “burn” more fat than those on the IF-free diet.

Intermittent Fasting Myths

1. IF helps to lose weight without a calorie deficit

This is a MYTH because, without a calorie deficit, the fact of the presence of IF does not allow you to lose weight. There is no scientific evidence for this fact, which in general is not so strange – the laws of thermodynamics are generally the same for everyone.

Well, in fact, controlled studies have shown that changing the frequency of food in any case – either more often or less – has no effect on energy expenditure or weight loss.

In fairness, it should be noted that there are at least three studies that have shown an increase in energy expenditure after about 36-72 hours of fasting. But this increase is so small that it is unlikely to have a significant impact on weight loss.

In general, the bottom line is that changing the frequency of meals – including the use of IF – does not affect weight loss.

For weight loss, it is important how many calories are received during the day and how much energy is spent by the body during the day: if there are more calories, then you gain weight (even with IF). If less, you lose weight (it does not matter if you are on IF or not).

2. IF helps to lose weight predominantly through fat, and retain more muscle than normal calorie restriction

Studies comparing weight loss using IF and simply calorie restriction show that people lose about the same amount of weight.

A study using dual-energy X-ray absorptiometry (DXA) did not find any difference in body composition after comparing 14 days of the alternative day fasting versus the continuous calorie restriction diet.

Recently the proponents of this myth have cited a large survey study – Varady, K.A. (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obesity Reviews. 12 (7),593-601.

In which the author concluded that, under comparable conditions, losing weight on a calorie deficit with the use of IF allows you to save 15% more muscle than with simple calorie restriction (without IF).

But analyzing the study, we understand that there are too many flaws to argue that this is true:

  • There is a problem with control over the subjects in the course of most studies: for example, the subjects took their word for food intake. As a result, it is not clear how accurate the data on the amount of protein/calories consumed in the experiment are, which, as a result, could affect body composition.
  • In studies where IF was studied, Bioimpedance was used as a method for measuring body composition, and this is not the best choice for accurate analysis.
  • Physical exercise was present only in one of the numerous researches. And as you know, this is a very important component of the issue of maintaining muscle mass while losing weight. So it is possible that any differences in body composition between Intermittent Fasting and Daily Calorie Restriction users would have disappeared if the studies included exercise, especially strength training.
  • There is a significant difference in the timing of the study of those who were on Intermittent fasting (12 weeks – the maximum, and most of them even shorter) and those who were on the daily calorie restriction (24 weeks – the maximum). Due to the fact that IF studies were rather short (most of them), the composition of body and weight (and do not forget that they are measured by bioimpedance) is strongly influenced by water (which drains out rather quickly, especially at first). So the shorter the studies, the more impressive evidence they can provide, but the results need to be measured in the long term.
  • Most of these studies have involved overweight or obese people, and there is no data for people without these problems.
  • Researchers compared results between very different studies. This means that the differences in the percentage of muscle loss may have been related to differences in study design.
3. IF helps to make the process of maintaining a calorie deficit easier by reducing hunger, which makes it more comfortable with losing fat (since you can spend more time on a diet without serious psychological discomfort)

Most likely, this is TRUE. However, research on this issue is not unambiguous. Somewhere the subjects still complained about a strong feeling of hunger during the period of IF.

Somewhere they said, on the contrary, that over time the organism becomes addictive, and hunger is no longer felt so strongly.

Many people really get used to periods of hunger, and the body no longer reacts so strongly to it in the period of IF.

Excerpt from Interview With Alan Aragon


Intermittent fasting has become very popular in recent years. What do you think about this? Panacea or fad?

“I think that the popularity of intermittent fasting work (IF) is, for the most part, a well-founded science.

 Scientists are well aware that research does not support the notion that eating smaller meals more often maintains your metabolic rate better than eating smaller, larger meals.

In addition, research has also failed to support the idea that small, frequent meals are necessary to maintain muscle mass.

The evidence also suggests that overall there is no threat to muscle retention during the diet when the frequency of meals is reduced daily or intermittently throughout the week.

In fact, some studies have shown excellent results in maintaining lean muscle mass with IFs while on a low-calorie diet.

However, this may be due to the measurement error inherent in the bioelectrical analysis of resistance (it measures the percentage of body fat – ed.).

It should also be noted that IF studies still do not contain structured research protocols.

While IF has a scientific foundation, it has also created a number of over-zealous followers who preach its universal need to optimize body composition and health.

Objectively, IF is a great option for those who prefer the convenience and luxury of large meals, not to mention the ease of preparing and transporting food throughout the day.


Any significant superiority of the metabolic effects of IF over traditional nutritional models is speculation today.

So far, IF has been consistently highlighted in light of the maintenance of lean muscle mass during dieting, but its advantage over normal eating frequency in terms of strength and muscle hypertrophy remains questionable, at least in formal studies.

There are many hypotheses in this area, but none of them has yet been scientifically confirmed.

Currently, the frequency of meals that is optimal for strength and muscle growth remains a mystery. This conundrum is likely to start opening up in short-term observations that some groups will furiously promote. If there is some correlation in history, then short-term observations will be followed by more detailed and long-term studies that will shake old beliefs. Anyway, when that happens, I’ll keep my popcorn ready.

Finally, I would like to add that I noticed the greatest effect among adherents of intermittent fasting work due to the fact that IF takes into account the individual characteristics of each person in their food intake.

Some people make more progress on small, frequent meals, while others on large and infrequent meals (etc.).

The theoretical benefits of a particular dietary approach come directly from someone’s personal preference, commitment, or ability.


  • Intermittent fasting work, in terms of using it for weight loss (fat burning), has no advantage over regular calorie restriction.
  • Likewise, intermittent fasting has no advantages over regular calorie restriction: neither in changes in body composition, nor in improving insulin sensitivity, nor in controlling blood glucose levels, nor in thyroid hormone, cortisol, and sex hormone levels.
  • Intermittent fasting is a handy tool for controlling hunger on a diet, but it is not a unique and super effective method for fat burning and maintaining muscle mass.


  1. Seimon RV et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418 Pt 2:153-72. doi: 10.1016/j.mce.2015.09.014. Epub 2015 Sep 16 [PubMed]
  2. Grant M Tinsley et al. Intermittent fasting combined with resistance training: effects on body composition, muscular performance, and dietary intake. Poster presentation [JISSN]
  3. An Objective Look at Intermittent Fasting By Alan Aragon & Ryan Zielonka
  4. Will Intermittent Fasting Help You Lose Weight? By Armi Legge.

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