2023-12-29 11:00:00
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 are obese, 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 regarding the essential nutrients contained. It thus helps to identify and promote a better diet by choosing healthier foods.
The promotion of 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, in recent years, interesting beneficial effects for our health, provided however that several principles are respected.
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Store energy in the form of adipose tissue
This so-called “intermittent” fasting refers to the fact of alternating phases where we 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 to adapt 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.
READ ALSO Should we favor frozen vegetables and fruits? 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 capacity to store energy in the form of adipose tissue has long been a selective advantage for getting through periods of food shortage!
Since antiquity
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 once more in the United States, particularly thanks to Dr. Edward Hooker Dewey, who suggested eating less by skipping breakfast. With his work No-Breakfast Plan and the Fasting-cure (The No-Breakfast Plan and the Fasting CureMax Apart editions, available on Kindle), he is one of the inventors of intermittent fasting.
Three approaches
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.
Le « eat-stop-eat ». Proposed by Brad Pilon in his book Eat Stop Eatthe principle is to alternate days where we eat normally and days without eating, with two non-consecutive fasting days during the week.
The “5:2” method. Developed in the 2000s by doctors Michelle Harvie and Tony Howell, it alternates, during the week, between days where you eat normally and two days – which can be consecutive – where you reduce your caloric intake from 70 to 75 %.
“Time-limited eating” (or « time-restricted fasting »). This method is the most popular and most studied currently. It consists of reducing your food intake window to between six hours and ten hours per day, and therefore fasting between fourteen and eighteen hours during the day.
For the “eat-stop-eat” and “5:2” approaches, relatively few scientific studies have been carried out. The limited data available have shown that they can be effective for weight loss 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 resulted in a weight loss of 3 to 6 kg in participants.
READ ALSO Should you become vegetarian for better health? However, because these two methods are very restrictive, they can cause 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 “yo-yo” type behaviors. This phenomenon is common when trying to lose weight by restricting yourself. Initially, there is weight loss, but the restrictions can generate frustrations which risk encouraging the return of old eating habits, themselves associated with weight regain.
Benefits
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 “time-restricted eating starting in the morning”;
when eating meals begins with midday lunch. This time we are talking regarding « late time-restricted feeding » or “time-restricted eating 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 weight loss 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, Ram Babu Singh’s team (from Halberg Hospital and Research Institute, India) showed positive results only in the group where participants ate in the morning, and not in participants who ate from midday and with the last food intake following 8 p.m.
Food quality and quantity
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 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 is from morning around 8 a.m. to 9 a.m. hours (at sunrise) until 7 p.m. (when the sun begins to set, depending on the season). Not eating breakfast and eating following 7 p.m. promotes dysregulation of circadian rhythms and increases the risk of developing metabolic diseases.
Be careful, however: if time-limited eating seems to be a good approach with regard to metabolic health, much remains to be understood regarding its functioning and optimizing its effects… Work from 2022 has thus not shown any differences in terms of 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.
READ ALSO What is the best bread for health? 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 twelve to twenty hours a 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.
A typical day
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., a lunch around noon and finally bringing 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:
the nutritional quality of the products we eat. You should favor the consumption of complex carbohydrates, such as whole grains, good fats rich in essential fatty acids, and have a sufficient intake of proteins, which can come from eggs, fish, unprocessed animal products but also from vegetable proteins. ;
establishing good eating habits;
and an appropriate level of physical activity – for example at least 30 minutes of brisk walking per day.
* Anouk Charlot is a doctoral student at the University of Strasbourg; Joffrey Customs is a university lecturer and hospital practitioner in physiology, at the Faculty of Medicine, University of Strasbourg.
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