Intermittent fasting

What is intermittent fasting?

An eating methodology that relies on periodic food (calorie) deprivation for periods of varying duration, followed by “windows” of eating.

Variants vary in application, and the fasting phase, during which no calories are taken, can range from 20 to 36 hours.

A ‘lighter’ interpretation with a 16-hour fasting period followed by an 8-hour interval of food intake is also common, although there is debate as to whether such an approach can be classified as intermittent fasting.

Why intermittent fasting is popular?

The reason fasting is the basis of the system is that it does several things in short intervals of time that a systematic three or four times a day meal plan cannot do:

It increases insulin sensitivity – this effect of intermittent fasting is not fully established at this stage, as almost all experiments that confirm it also shows weight loss in overweight people. It is not clear whether intermittent fasting led to the improvement in glucose metabolism and insulin sensitivity or the weight loss.
It is easy to create a negative calorie balance on the scale of a calorie week – some people find it easier to be more aggressive in fasting and in calorie deficit only 1-2 days a week, rather than less calories each day.
The periods are long enough to start enhanced fat burning process and not long enough to start a serious decline in overall metabolism.
It is easier for people with a busy lifestyle, since with a proper fasting window of time, they don’t have to think about eating.
Studies conducted with rats have shown life expectancy prolongation when fed the intermittent fasting model even without a significant calorie deficit.

The reason for the overall beneficial effects of prolonged fasting is thought to be in the reduced caloric intake and moderate ketosis.

In studies with laboratory animals subjected to several weeks of PF, the following confirmed biochemical parameters are mentioned: increased insulin sensitivity, decreased blood glucose levels, increased IGF-1 growth factor, decreased leptin levels, increased beta-hydroxybutyrate levels.

The effects are better insulin utilization, increased growth stimulus, decreased fat deposition, increased fat metabolism activity, increased antioxidant activity, and better protection against toxins and free radicals.

Human studies are in their beginning stages but confirm many of the findings in animals.

Different types of Intermittent Fasting

Based on the length of fasting and the periods between two fasts, the methods using the principle are:

Fasting 1 to 3 times a week.
Daily fasts (Warrior diet, Leangains, fast -5);
Mixed methodologies.
Fasting 1 to 3 times a week (1-3/week)

Simply put, you fast once to three times a week for 20 to 36 hours each day or two, including sleep time.

Example: If we choose to fast on Tuesday, the fast starts after an early dinner on Monday and ends with a late lunch on Wednesday.

This system in some people is a more successful way of achieving a negative calorie balance on a weekly basis and a greater potential tool for lowering weekly calorie intake compared to monotonic regimens (eating the same kcal every day).

Example with a simple account:

Person X has a daily requirement of 2 000 kcal to maintain weight (=BMR* factor according to the formula).
He/she chooses to follow a monotonic balanced diet of 1 500 kcal, for 4 weeks.
His weekly energy expenditure is approximately 14 000 kcal.
With 1 500 x 7 days per day = 10 500 kcal per week. Intake of only that much energy will create a shortfall of 3,500 kcal/week.
If he/she chooses to use an even, balanced diet over 4 days with 2,000 kcal/day and 3 fasts of 24 hours each, the picture would be:
4 x 2,000 = 8,000 kcal/week, resulting in a 6,000-kcal calorie deficit for the week.
Daily fasts (Warrior Diet, Leangain, Fast -5)

The main calories for the day, including most of the carbohydrate portion, are consumed in a small window of time, four to five hours per day. Most often, this is the time from late afternoon to dinner. The specifics vary with different popular methods using the principle of daily fasts.

Mixed methodologies

Here several large fasts are combined with several small ones and days of normal eating.

Example: Monday, Wednesday and Friday normal eating, Tuesday and Thursday fasting, and on the weekend fasting during the active part of the day (or night) and eating in a limited time interval from late afternoon to dinner.

Who should not implement intermittent fasting?

In general, with carefully calculated calorie balance for a week, the principle and the methodologies that follow it do not pose a danger to the health of a healthy person of active age.

The possible risks in applying PF are specific:

Daily fasting: possibility of overloading the kidneys and liver with proteins (uric acid and urate) in case of overeating in the intensive feeding period, but this can be a problem mainly in people with liver and kidney diseases.

Hypoglycemic attacks and drop in blood pressure – avoid this type of eating if you have fluctuating blood pressure or if you are an insulin-dependent person with diabetes because of the difficulty in calculating insulin dose and monitoring the half-life of the injected insulin.

All-day fasting 1-3/week: reduced risk of urea and urate poisoning compared with daily fasting, and increased risk of hypoglycemia compared with daily fasting. Administer under dietary control if you have diabetes, no matter if you are insulin dependent or not.

Who will benefit from intermittent fasting?

Intermittent fasting has its proven benefits for people who are about to lose excess weight. The main reason is the ability to easily achieve a large calorie deficit in a week/month, although not all people are able to stick with this way of eating.

It is also suitable for sedentary people, overweight (obese) elderly people, people with a high fat percentage and low active mass, who cannot provide additional energy expenditure through physical activity.

It may also be a good option for people engaged in intellectual work or those with low physical activity in their working day, as well as for people with a very busy daily routine who want to save themselves time of meal – prepping during the day.

For which individuals it is rather inappropriate way of eating?

Intermittent fasting is not common for bodybuilders and people aiming to gain muscle mass and is rather inappropriate for them. To put it another way, if you are an athlete with a fast metabolism (high active weight + high kcal consumption/day), this method of eating may be more detrimental than beneficial to you. It’s absolutely possible to gain muscle mass and train hard through intermittent fasting, however it’s just not optimal.
It can cause a drop in blood pressure and lowered blood sugar, so people with low chronic blood pressure should be cautious.
It is not recommended for insulin-dependent diabetics because of purely practical problems in the regulation of insulin intake.
Leads to irritability on ‘fasting days’. Increases aggressive behavioral pattern. For hyperactive and nervous people, it is better to give up PF. Attacks of “food stuffing” are possible.
Fasting is a problem in ulcers and gastritis.
People with unstable mental health and problems with self-perception and acceptance should not engage in PF. This includes bulimics and anorexics or those who are likely to go to extremes.
The majority of women do not respond well to intermittent fasting as the female hormonal balance is sensitive to the type, quantity and frequency of feeding. The reproductive system is affected not only by body fat percentage but also by overall calorie balance. There are women who tend to maintain too strict a calorie deficit, and with intermittent fasting this possibility is even greater.
With what type of activity, you can combine intermittent fasting?

Exercise and IF application have similar effects as stimuli and end effects on the body and metabolism.

To maximize the effect, you need to follow a program that ensures that the calories in your regular days will fuel your body so that you don’t end up in a calorie crisis.

So be careful when calculating your calorie balance – do it on a weekly basis to see how much % you are in negative calorie balance compared to your norm.

Daily fasting

It is suitable for any type of training load, provided that the person adapts and is used to exercise on an empty stomach. In the beginning it may be possible to feel dizzy, but with time most people manage to adapt.

All-day fasting 1-3/week – regular days

There are no training restrictions. All types of sport activities are suitable, the duration of which will not interfere with regular mealtimes.

All-day fasting 1-3/week – half fasting days

Moderate and low volume strength and conditioning workouts are appropriate. Low-intensity workouts with high duration and low energy expenditure such as yoga, pilates, stretching, isometrics. May incorporate interval cardio into a short session.

All-day fasting 1-3/week – fasting days

Stick to low-intensity workouts with short duration and low energy expenditure – pilates, yoga, stretching, isometrics, tai chi, etc. If the fasting day is the first in the series or the fasting is still in the early hours, you can probably afford some more intense workouts, but the further the complete lack of food progresses, the greater the risk of feeling dizzy.

Mixed approaches

Here things vary enormously depending on the specifics of the methodology. General conclusions like the previous two fasting methodologies are not possible. Such regimens are usually either developed into a whole concept as a system of nutrition and training or are made individually by an expert for a specific client.

To sum up

Intermittent fasting has its proven benefits and positive impact on the human body.

While not all people can go long hours (or even days) without food, the many different intermittent fasting protocols allow considerable flexibility. If you choose to follow it and have no experience with long periods of time without calorie intake, start with a lighter version of the application, gradually increasing the hours of the fasting phase and in parallel decreasing the time span during which you eat.

One of the main things that intermittent fasting has been researched for in the scientific literature is as a means of aiding weight loss. At this point, the data does not show greater (but not less) effectiveness compared to other ways of eating, but it does appear to be an easier plan for many people to follow. If your goals are to lose excess weight and frequent food intake tends to make you hungrier, or if it mentally stresses you out by making you feel like you’re constantly thinking about eating, then it’s worth trying some form of intermittent fasting.

However, if you’re the type of person who aims for optimal muscle gain and maximum athletic performance, then our advice is to either go for a different diet or choose a protocol with small fasting windows, such as 16/8. Remember, there’s nothing special about fasting, no matter what claims you see online. For some people it’s a convenient diet method. The most important thing is our energy intake, whether we are in a calorie surplus, deficit, or maintenance.

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