Understanding Intermittent Fasting and Its Effects on Health: A Comprehensive Guide

2023-12-28 21:44:51

Intermittent fasting, an attractive strategy… but complicated to implement

Anouk Charlot, University of Strasbourg et Joffrey Customs, University of Strasbourg

Health and good eating habits are at the heart of modern issues. Indeed, faced with the increase in the prevalence of metabolic diseases such as overweight and obesity (13% of adults obese, 39% overweight according to the WHO), the importance of having a balanced and adapted diet to limit these risks is increasingly present in the collective mind.

Public health policies, scientific recommendations and health organizations are trying to fight this scourge with preventive approaches. For example, thenutritional labeling on food packaging provides consumers with simplified information on the essential nutrients contained. It thus helps to identify and promote a better diet in choosing healthier foods.

Promoting slogans such as “five fruits and vegetables a day”, the national health nutrition program “Eat Move” or even prevention campaigns are also used to warn and promote healthy eating behaviors.

However, “what we eat” is not enough… We must keep in mind that “when and how often we eat” also plays an important role. This is how the concept of “intermittent fasting” was born, which has demonstrated interesting beneficial effects for our health in recent years, provided, however, that we respect several principles so as not to do anything.

We finally know why the rooster crows in the morning!

Fasting, a long history…

This so-called intermittent fasting refers to the fact of alternating phases where you do not eat (more or less long) and periods of food intake.

Physiologically, fasting is a behavior that is not exceptional. It is even common among animals which are forced toadapt to their ecological and physiological constraints. For example, during periods of hibernation, reproduction, during moulting, or in cases of illness, some have no other choice but to fast.

In humans, this behavior might also be adopted – voluntarily or not. If we look back 30,000 years or more, we can see that some of our ancestors A wise man were faced with periods of fasting.

As a very active hunter-gatherer, its survival depended on sufficient food intake. However, its lifestyle, combined with seasonal variations, changing climatic conditions and unpredictable success when searching for food might lead to periods of fasting. This is also why our great ability to store energy in the form of adipose tissue has long been a selective advantage to get through periods of food shortage!

Fasting has been practiced intentionally since Antiquity, recommended in particular by Hippocrates and Galen (center, top), then throughout the Middle Ages.
Dioscorides of Viennes (codex 6th century)

Voluntary food abstinence is also widely present throughout human history. In a religious context, fasting is present in Christianity (Lent), the Islamic religion (Ramadan), but also Judaism, Hinduism and Buddhism.

In medicine, it has been practiced since Antiquity since Hippocrates and Galen already prescribed it to patients. He is also found in the Middle Ages in the writings of the Persian doctor Avicenna or the Swiss Paracelsus, to improve health.

More recently, it was in the 19th century that this practice became popular once more in the United States, particularly thanks to Dr. Edward Hooker Dewey who suggested eating less by skipping breakfast. With his book “No-Breakfast Plan and the Fasting-cure”, he is one of the inventors of intermittent fasting.

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Intermittent fasting… yes, but which one?

Now very popular, the term “intermittent fasting” actually brings together several approaches, the principles of which differ slightly. It is important to note that regardless of the method used, the restrictions only affect food – never water intake.

Summary of different intermittent fasting methods.
Anouk Charlot, Author provided

And what does science say regarding it?

Results vary depending on the strategy adopted.

For the “eat-stop-eat” and 5:2 approaches, relatively few scientific studies have been carried out. The scant data available showed that they might be effective for weight loss et improve certain metabolic parameters such as fasting blood sugar. For example, Surabhi Bhutani (University of Illinois) showed that using the 5:2 method for three months resulted in weight loss of 3 to 6 kg among participants.

However, these two methods being very restrictive, they can lead to Side effects during days of total fasting or severe calorie restriction – hunger, negative effects on mood, risk of hypoglycemia, etc.

In the longer term, restriction also increases the risk of developing or worsening eating disorders, and increases the risk of adopting behaviors of “type yo-yo”. This phenomenon is common when trying to lose weight by restricting yourself: initially, there is weight loss, but the restrictions can generate frustration… which risks encouraging the return of old eating habits, themselves. associated to regain weight.

The most studied method is that with food intake every day but limited in time. Two “time slots” are often observed:

• When food intake begins with breakfast and ends in the late followingnoon. We speak in English of “early time-restricted feeding”, or “eating limited in time from the morning”;
• When eating meals begins with lunch. This time we are talking regarding “late time-restricted eating”, or “eating limited in time from midday”.

This approach seems useful for improving the regulation of one’s metabolism and reducing the risk of metabolic diseases… However, these beneficial results do not seem to be equivalent depending on the time slot chosen. When food intake begins in the morning, studies have found a weightloss and improvements in insulin sensitivity.

Conversely, when meals begin at midday and end in the evening, the beneficial effects would be less significant, or even absent. For example, the team of Ram Babu Singh (from Halberg Hospital and Research Institute, India) showed positive results only in the group where participants ate in the morningand not in participants who ate from midday and with the last food intake following 8 p.m.

Why such a difference ?

Our internal clock and circadian rhythms seem to be to blame. Indeed, the advantage of time-limited eating starting in the morning is to make the periods of food intake and fasting coincide with our biological clock.

In our previous articlewe explained that in response to light cycles, our body produces hormones cyclically to adapt our food intake to the body’s energy needs: the optimal period for eating is from the morning around 8-9 a.m. (at sunrise ) until 7 p.m. (when the sun begins to set, depending on the season).

Not having breakfast and eating following 7 p.m. promotes dysregulation of circadian rhythms, and increase the risk of developing metabolic diseases.

Be careful, however: while time-limited eating seems to be a good approach when it comes to metabolic health, much remains to be understood regarding how it works and optimize its effects… Work in 2022 has thus not been did not show differences in weight loss between opting for morning or late food intake… On the other hand, it played on the appetite felt during the day – this time to the advantage of the former.

And beyond the time of day when it seems preferable to eat, other parameters may be important and which are not always measured in the studies carried out: quality and quantity of foods absorbed, duration of the fasting period. (which can extend from 12 to 20 hours per day), etc.

In addition, each individual has their own metabolism, and may respond differently to fasting. New studies, better controlled and more complete, are therefore necessary to confirm the potential benefits of these methods and understand the mechanisms involved in their effects. This alone will make it possible to develop approaches adapted to the needs of each individual.

In practice, what to do?

The most suitable method to at least avoid disrupting your circadian clock (and limit the risk of frustration or eating disorders) seems to be time-limited food intake by synchronizing your meals with circadian rhythms.

Thus, a typical day might be organized with a hearty breakfast in the morning, between 6 a.m. and 8 a.m., lunch around noon and finally bring forward your dinner so that it takes place between 4 p.m. and 6 p.m. depending on the season.

Which is not necessarily easy to reconcile with your social life… It can be complicated to practice intermittent fasting for a family, when you practice a sporting activity in the early evening or when you work in the evening until 7 p.m. or 8 p.m.

One solution would be to opt for a hearty breakfast and a low-calorie meal in the evening – preferably without starches or sugars, so as not to risk shifting your biological clock.

Other important things to watch out for, beyond the right time to eat:

Typical day and preferred foods to practice time-limited eating.
Anouk Charlot, Author provided

What to conclude?

“Chrono-nutrition” is on the rise and intermittent fasting seems to be effective in improving metabolic health… but as we have seen, it is not a panacea. And we must ensure that the periods of fasting and food intake are consistent with our biological clock.

Faced with the various existing methods and the potential risks, information is still incomplete. It is essential to continue research to better decipher their effects. Currently, there is no no general consensus yet on the ideal time to eat/fast, or on the optimal duration of each period. Moreover, these parameters may be different from one person to another, particularly depending on their genetic heritage, history and lifestyle. It is therefore important to consider the use of this dietary strategy with qualified health professionals, in order to implement a healthy and balanced diet which will limit the risk of deficiencies and complications.

Anouk CharlotPhD student, University of Strasbourg et Joffrey CustomsMCU-PH in physiology, faculty of medicine, University of Strasbourg

This article is republished from The Conversation sous licence Creative Commons. Lire l’article original.

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