Intermittent Fasting - How Effective Is It Really?


Intermittent fasting - also known as intermittent fasting - is a certain form of nutrition that is often used as a measure to reduce weight and is then rated as a form of diet.
The principle of intermittent fasting consists in alternating between times of fasting and times of food consumption in a regular rhythm.
There are different types of intermittent fasting, they differ in which interval is chosen for food abstinence.
Outside of the fasting intervals you can eat normally without counting calories.
For this reason, and because of the resounding successes in studies on animal models, intermittent fasting is one of the forms of diet that is enjoying increasing interest.

Instructions for intermittent fasting

There are different types of intermittent fasting.
They differ in terms of the respective fasting periods.
The two most popular and most frequently used variants are the 5: 2 variant and the 16: 8 variant.

First, all variants of intermittent fasting are briefly described, followed by more detailed instructions on how exactly intermittent fasting works.

With the 5: 2 variant, the calorie intake is reduced to 500 (women) to 600 (men) kcal per day on two non-consecutive days; you can eat normally on the remaining 5 days of the week.
The 16: 8 variant, which is the most popular variant of intermittent fasting, fasts for 16 hours of the day, the remaining 8 hours can be eaten without restriction.

Alternate Day Fasting, also known as eat-stop-eat or alternating fasting, is rarely used and fasts every other day with a maximum calorie intake of around 500 kcal.
You can eat without restrictions on the remaining days.

The 16: 8 variant

The 16: 8 variant is most often chosen for intermittent fasting.
If you have decided to fast according to this variant, you should first decide whether you want to skip breakfast or dinner as the main meal in order to adhere to 16 fasting hours per day at the end.

People who cannot start the day well without their breakfast can, for example, have breakfast of their choice at 8 a.m. as usual, but are then not allowed to eat anything after 4 p.m.
People who have to get up in the early hours of the morning should therefore consider postponing breakfast at least a little later. Otherwise, for example, with breakfast at 6 a.m., the 16-hour fasting period starts at 2 p.m.

People who would rather skip breakfast than dinner can have their last meal at 7 p.m., for example.
The following fasting period ends at 11 a.m., from this point onwards, for example, a late breakfast or an early lunch can be taken.

It is important with intermittent fasting that sufficient fluid intake is ensured during the fasting hours.
Water and unsweetened teas as well as coffee without milk are allowed.
Especially for people who prefer to skip breakfast, a morning coffee or tea is a small breakfast substitute for a healthy start to the day.
But what about the 8 hours in which you can eat without restrictions? Basically, with intermittent fasting, you can eat normally and without reducing calories during these hours.
However, it is important for success - if weight reduction is the goal - that there is no excessive calorie intake in the 8 hours of the eating phase. Usually this is not necessary at all, as the body would quickly be overwhelmed with 3 meals in 8 hours.

When you start intermittent fasting according to the 16: 8 method, you will notice relatively quickly that 2 main meals within the 8 hours are completely sufficient.
Binge eating with very high calorie foods should of course be avoided if possible, as otherwise the effect of fasting can be significantly reduced. You should therefore pay attention to a balanced diet during the 8 hours of eating, but you do not have to forego anything.
A schnitzel with french fries or one or the other chocolate bar can definitely be on the menu - in moderation.

The 15: 2 variant

With the 15: 2 variant, it usually makes sense to set 2 fixed days at the beginning on which you will fast.
This makes it easier for the body - and also the psyche - to implement the fasting diet.
On the two days of fasting, the calorie intake is limited to 500-600 kcal.

It is a good idea to cover the calories with protein-rich foods, vegetables and whole grains.
Here, too, it is extremely important to ensure that you are drinking enough fluids.
If you want something spicy, you can also use vegetable broth, for example.
On the one hand, it serves as a liquid supplier, but on the other hand it also satisfies the urge for something hearty.

Good examples of snacks on the two days of fasting are:

  • Oatmeal with low-fat quark or cottage cheese and some berries,
  • Dishes with lean fish or meat,
  • raw or cooked vegetables,
  • different salats,
  • Eggs in all forms of preparation

How does it work at home?

First, you should choose one of the intermittent fasting methods.
Overall, the 16: 8 method seems to be the method that is easiest to integrate into everyday life and to be persistent.
Once you have decided on a variant, you should create a kind of schedule.

With a 16: 8 fast you should plan when the first and when the last meal can be consumed.
With 5: 2 fasting, you should specify the two days of fasting.
It's best to put it all down in writing.

With the 5: 2 method, it is also a good idea to think about which snacks you want to eat on the fasting days.
It's best to have the essential ingredients at home.
Because, especially at the beginning of intermittent fasting, it can be difficult to go shopping on an empty stomach.

Even with the 16: 8 method, it can't hurt to deal with the topic of healthy and balanced nutrition and maybe pick out some appropriate recipes.
In addition, you should always ensure sufficient fluid intake - at least 2 liters a day.

If intermittent fasting is started in order to achieve weight loss, it is advisable to document the initial weight.
It is often helpful to also measure and record the hip circumference.
It is important that you do not weigh yourself every day after starting intermittent fasting.
Body weight is subject to significant daily fluctuations, so it can often be rather frustrating to weigh yourself frequently.
It is a good idea to weigh yourself on a fixed day during the week.
If possible, under the same conditions, preferably in the morning after using the toilet and before the first meal.

How long should you do intermittent fasting?

Intermittent fasting is one of the diets, but - in contrast to many other diet forms - it is also suitable for everyday use over the long term.
It is therefore also viewed as a useful permanent form of nutrition.
The 16: 8 method in particular can be suitable for everyday use over the long term.
So there is no time limit for intermittent fasting.

People who start intermittent fasting can therefore decide for themselves whether they want to integrate fasting permanently into their everyday life or whether they want to stop it when the desired weight goal has been achieved.

How much can I / should I lose weight with intermittent fasting?

There are no guidelines on how much can or should be lost with intermittent fasting.
This depends primarily on the initial weight.

People who are very overweight usually lose weight faster at the beginning of a diet than people who weigh just a few pounds too much.
With intermittent fasting, no change in diet is prescribed, so that the type of diet during the eating times is so variable that no comparable information can be given on how much weight can be lost with this type of diet.

Daily exercise also plays a crucial role in weight loss.
How much can be lost with intermittent fasting depends on the starting weight, the type of diet and the physical activity and is very different from each individual.

The following article may also be of interest to you: Lose weight without hunger - is that possible?

Side effects of intermittent fasting

Especially in the first days of intermittent fasting, the change for the body during the fasting phase can lead to dizziness and fatigue.
Reduced physical resilience, headaches, an increased sensation of cold as well as concentration disorders and sweating can occur.

On the other hand, many people who have started intermittent fasting report an increased ability to perform and concentrate after a few days. Basically, you should keep in mind that with variants like the 5: 2 method, the body may be a little less productive on the fasting days.

You can find out here how you can improve your concentration through concentration training:
Concentration training - better concentration through brain games?

Diarrhea during intermittent fasting

A change in diet - and this is intermittent fasting in the broader sense - can have a wide variety of effects on the body.
Every body reacts differently to the changed food intake.
Slight diarrhea can be a possible symptom when starting intermittent fasting.

However, it can also lead to slight blockages.
Overall, however, these complaints are usually nothing to worry about.
The metabolism should have returned to normal after a short period of acclimatization and the symptoms should disappear.
If this is not the case, it may be advisable to discuss the symptoms with a doctor.

For information on how to eat when you have diarrhea, see: Diet for diarrhea

Headache during intermittent fasting

The body reacts to various changes in lifestyle with a headache.
A change in diet can also cause headaches.
These can occur especially in the first days of intermittent fasting.
However, they should disappear again quickly - provided that a balanced diet and, in particular, a sufficient amount of water are consumed.

Criticism of intermittent fasting

The hype about intermittent fasting arose after it was impressively demonstrated in an animal model that regular fasting leads to both a reduction in body weight and the risk of developing chronic cardiovascular diseases or diabetes.
Intermittent fasting also reduced the risk of cancer in the animal model.
Overall, intermittent fasting in the animal model showed a life-prolonging effect.

Studies on intermittent fasting in humans are hardly available and only in very small numbers of cases.
However, even this small number of studies suggests that the effects of intermittent fasting in the animal model cannot simply be transferred to humans.
Obviously, intermittent fasting seems to do neither better nor worse in terms of weight loss compared to diets that consistently watch for a calorie deficit.
Also with regard to the question of whether intermittent fasting can lead to an improvement in glucose metabolism and thus to a reduction in diabetes diseases, there are no reliable data so far.
However, recent studies on animal models have indicated that the opposite effect, i.e. an increase in the risk of diabetes from intermittent fasting, could be a conceivable consequence.
With regard to the question of whether intermittent fasting can reduce the rate of diabetes, the study situation is currently ambivalent.
So far there are no valid long-term studies on humans.

The main criticism of intermittent fasting is currently that the studies that have found great success with intermittent fasting were all studies on animal models and that there are no meaningful studies on intermittent fasting in humans.
So far there is no reliable evidence that intermittent fasting has any advantages over conventional weight loss diets.
However, the coming years will certainly bring new insights into this.

Basically, intermittent fasting seems to have potential, both in terms of possible effects and adherence (i.e. long-term adherence). Another point of criticism of intermittent fasting is that hardly any guidelines are given with regard to the choice of food.
Therefore, there is a risk that, despite fasting periods, an unhealthy and unbalanced diet will continue during the eating times.
Intermittent fasting does not provide for a change in diet.
This can have both advantages and disadvantages.

Would you like to eat healthily, but you don't know exactly what to do without?
Then read our related article:
Healthy Eating - Everything You Should Know!

What are the risks / dangers of intermittent fasting?

Possible side effects of intermittent fasting have been described above.
Intermittent fasting does not usually involve any risks or dangers for a healthy person.
Intermittent fasting - like any other type of fasting - is not recommended for children and adolescents, pregnant and breastfeeding women, as these groups of people can lead to incalculable risks and side effects.
Older people should also first consult a doctor before deciding on intermittent fasting, as the body may no longer be able to compensate for the fasting periods sufficiently well.

People with certain pre-existing conditions should generally avoid intermittent fasting.
These include patients with an underactive or overactive thyroid that has not been adequately controlled with medication, with dementia and eating disorders (especially anorexia nervosa).
In the case of various other diseases, a doctor should always be consulted before the start of the fast and the fast should be monitored regularly by a doctor. These include type 1 diabetes mellitus, significant impairment of liver and kidney function, cancer of all kinds and gout.

Diabetics who decide to fast must - regardless of whether it is type 1 or type 2 diabetes - consult their doctor before starting the fast, as the antidiabetic medication may have to be adjusted.
Otherwise there is a risk of severe, potentially life-threatening hypoglycaemia.

How can I avoid the yo-yo effect during intermittent fasting?

Intermittent fasting is said to be one of the few diets that does not have the dreaded yo-yo effect.
This is due to the fact that with intermittent fasting, significantly fewer calories are consumed not permanently, but only by the hour.
Because there is no permanent drastic reduction in calorie intake, the metabolism does not slow down and there is no breakdown of muscles.
As a result, following intermittent fasting - according to the theory - there is no yo-yo effect either, as the body was not forced into starvation metabolism. Intermittent fasting is also - in contrast to some other diets - a form of nutrition that - if desired - can be practiced permanently.

You can find out what the yo-yo effect is and why it occurs at:
The yo-yo effect - how and why does it happen?

Medical evaluation of intermittent fasting by

Intermittent fasting is a diet method that has its place.
Compared to numerous other forms of diet, there is no radical calorie restriction.
If at all, this reduction only takes place over a certain number of hours.
The 16: 8 method, in particular, is a sensible option for people who find it difficult to stick to diets.
Because you can eat normally for 8 hours a day, there are significantly fewer cravings and discipline problems.

Intermittent fasting can be disadvantageous for people who have a relatively unhealthy diet overall, as these eating habits are not changed by intermittent fasting, but only limited in time.
Intermittent fasting is therefore particularly recommended for people who like to eat a lot - but not almost exclusively unhealthily - and want to lose weight in a controlled manner by restricting their food intake by setting a time frame in the amount.

People who eat primarily unhealthy - that is, high in fat and carbohydrates - should, under certain circumstances, prefer a diet that aims to fundamentally change their diet.
There is nothing wrong with intermittent fasting in healthy people, as long as they are hydrated.
Intermittent fasting should - if weight reduction is the goal - be combined with regular physical endurance training like all other forms of diet.

Would you like to find out more about other forms of diet in order to find the right one for you?
You can find numerous other diets here: Diets - Overview

What alternative is there to intermittent fasting?

Intermittent fasting can be seen both as a diet and as a longer-term form of nutrition.
If intermittent fasting is viewed as a diet aimed at reducing weight, there are numerous alternatives.
The aim of all diets is to reduce the daily calorie intake so that a calorie deficit - i.e. a difference between calorie intake and calorie consumption - arises.
They are therefore also referred to as reduction diets.
Weight loss can only be achieved by maintaining a daily calorie deficit.
The many different diets actually only differ in the way in which the daily calorie deficit is achieved.

Examples of certain diet forms are, for example, the low-carb diet, in which as few carbohydrates as possible are consumed, the low-fat diet, in which fats are avoided, formula diets in which certain meals are replaced by ready-made drinks or nutrient powder and the calorie intake thus limited or the FDH ("eat half-eat") diet in which only half of everything should be eaten.

Other diet concepts, such as weight watchers, also have calorie reduction as their main goal.
However, they also provide support through certain point systems, buying guides and group exchanges to make dieting easier.

The Mediterranean diet is one of the diet forms that advocate permanent change in diet.
The advantage of such diets is that the risk of a yo-yo effect after a permanent change in diet is significantly lower than with simple reduction diets.

Which form of diet is the right one ultimately depends very much on your own eating habits, eating habits and your own discipline.

What are the costs of intermittent fasting?

Intermittent fasting is usually not associated with increased costs.
A certain number of hours is fasted, the rest of the day can then be eaten normally, without any guidelines for certain foods.

With variants such as 15: 2 intermittent fasting, you should not consume more than 500-600 kcal 2 days a week.
Protein-rich and wholesome snacks are recommended for these days.
Examples are given above.
But even these recipe ideas shouldn't put too much strain on the wallet.

Intermittent fasting is therefore a form of diet that does not mean a significant increase in food costs.