“Intermittent fasting” can be beneficial for our health… provided we respect certain principles, according to our partner
The Conversation
.
Now very popular, “intermittent fasting” brings together several approaches whose principles differ slightly.
But whichever method is used, the restrictions only affect food – never water intake.
This analysis was conducted by
Anouk Charlot
, doctoral student in physiology, and
Joffrey Zoll
, lecturer - hospital practitioner in physiology (both at the 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 obese adults, 39% overweight according to the WHO), the importance of having a balanced diet and adapted 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, nutrition labeling on food packaging provides consumers with simplified information about the essential nutrients contained.
It thus helps to identify and promote better eating by choosing healthier foods.
The promotion of slogans such as "five fruits and vegetables a day", the national health nutrition program "Eat and Move" or even prevention campaigns are also used to warn and promote healthy eating habits.
However, what we eat is not enough… Keep in mind that when and how often we eat also play an important role.
This is how the concept of “intermittent fasting” was born, which in recent years has demonstrated interesting beneficial effects for our health, provided however that several principles are respected so as not to do anything.
Fasting, a long history...
This so-called intermittent fasting refers to 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 in animals that are forced to adapt to their ecological and physiological constraints.
For example, during periods of hibernation, reproduction, during moulting, or even in the event of illness, some have no choice but to fast.
In humans, this behavior could also have been adopted – voluntarily or not.
If we go back 30,000 years or more, we can see that some of our
Homo sapiens
ancestors faced periods of fasting.
As a very active hunter-gatherer, his survival depended on sufficient food intake.
However, his lifestyle, associated with seasonal variations, changing climatic conditions and unpredictable success during his search for food could lead to periods of fasting.
This is also why our great capacity to store energy in the form of adipose tissue has long been a selective advantage in getting through periods of lack of food!
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.
It 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 again in the United States, more 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.
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 no matter which method is used, the restrictions only affect food – never water intake.
The “eat-stop-eat”.
Proposed by Brad Pilon in his book
Eat Stop Eat
, the principle is to alternate days when you eat normally, and days without eating, on the basis of two non-consecutive fasting days in the week.
The 5:2 method. Developed in the 2000s by doctors Michelle Harvie and Tony Howell, it alternates during the week between days when you eat normally and two days (which can be consecutive) when you reduce your caloric intake. 70 to 75%.
Time-restricted feeding.
This method is the most popular, and the most studied currently.
It consists of reducing your window of food intake between 6 and 10 hours a day, and therefore of fasting between 2 and 6 hours a day.
And what does science say?
The results vary depending on the strategy adopted.
For the “eat-stop-eat” and 5:2 approaches, relatively few scientific studies have been conducted.
The limited data available have shown that they may be effective in losing weight and improving 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 led to a weight loss of 3 to 6 kg in participants.
However, as both of these methods are very restrictive, they can cause side effects on days of total fasting or high calorie restriction – hunger, negative effects on mood, risk of hypoglycemia, etc.
In the longer term, the restriction also increases the risk of developing or worsening eating disorders, and promotes the risk of adopting “yo-yo type” behaviors.
This phenomenon is common when trying to lose weight by restricting yourself: at the start, there is indeed weight loss, but the restrictions can generate frustrations... which risk encouraging the return of old eating habits, themselves associated with weight gain.
The most studied method is the one 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 afternoon.
We speak in English of “early time-restricted feeding”, or “feeding limited in time from the morning”;
When meal intake begins with midday lunch.
This time we are talking about “late time-restricted feeding”, or “time-limited feeding from noon”.
This approach seems useful for improving the regulation of your 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 is started in the morning, studies have found weight loss and improvements in insulin sensitivity.
Conversely, when meals start at noon 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 the participants ate in the morning, and not in the participants who ate from noon and with the last food intake after 8 p.m.
Why such a difference?
Our internal clock and circadian rhythms seem to be involved.
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 a previous article, we 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 stretches from the morning around 8-9 a.m. (at sunrise) until 7 p.m. (when the sun begins to set, depending on the season).
Skipping breakfast and eating after 7 p.m. promote dysregulation of circadian rhythms and increase the risk of developing metabolic diseases.
Be careful, however: if time-restricted feeding seems to be a good approach with regard to metabolic health, much remains to be understood about its functioning and optimizing its effects... Work in 2022 has thus not shown any differences in terms of weight loss between the fact of opting for a morning or late food intake… On the other hand, it played on the appetite felt during the day – to the advantage this time of the first.
And beyond the time of day when it seems best to eat, other parameters may be important and which are not always measured in the studies carried out: quality and quantity of food absorbed, duration of the fasting period (which can range from 12 to 20 hours a day), etc.
In addition, each individual has their own metabolism, and may respond differently to fasting.
New, better controlled and more comprehensive studies are therefore needed 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 one.
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 could be organized with a hearty breakfast in the morning, between 6 a.m. and 8 a.m., a 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 sports 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:
The nutritional quality of the products we eat.
It is necessary to favor the consumption of complex carbohydrates, such as whole grains, good fats rich in essential fatty acids, and to have an adequate intake of proteins, which can come from eggs, fish, unprocessed animal products but also vegetable proteins. .
Establishing good eating habits
And an appropriate level of physical activity – for example at least 30 minutes of brisk walking per day.
What to conclude?
“Chrononutrition” 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.
OUR “FASTING” FILE
Faced with the various existing methods, and the potential risks, the information is still incomplete.
It is essential to continue research to better decipher their effects.
Currently, there is not yet a general consensus on the ideal time to eat/fast, or the optimal length of each period.
Moreover, these parameters may be different from one person to another, in particular according to their genetic heritage, history and way of life.
It is therefore important to consider the use of this dietary strategy with qualified health professionals, in order to establish a healthy and balanced diet that will limit the risk of deficiencies and complications.
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