Le jeûne intermittent : Parlez-en en bon...Parlez-en en mal, mais parlez-en !

Intermittent fasting: Talk about it good...Talk about it bad, but talk about it!

Intermittent fasting is probably one of the most popular dietary approaches in recent years & which continues to be talked about a lot today.

Some “demonize” this way of eating…

Others "idolate" him.

In an era where the internet makes information much more accessible than before & where diets / food fads are more topical than ever, I understand you being confused!

This blog will aim, in a neutral and transparent manner, to shed light on the subject and to present this food approach under its “ pros ” & its “ cons ”.

Intermittent Fasting: What is it?

First, it involves limiting your daily food intake according to a certain “window” of time. The approach that has been the most popular is the famous " 16-8 ". Fast for 16 consecutive hours & eat only for the next 8 hours.

For example, a person might decide to eat only between 12:00 p.m. & 8:00 p.m., then refrain from eating until noon the next day.

Others will instead opt for less "limiting" formulas, thus offering a larger "food window", such as the " 12-12 " for example. 12 hours of food period for 12 hours of fasting.

For Vs Against

Body well-being & energy

Intermittent fasting can be very interesting in the context of bodily well-being and improving digestion. Indeed, the gut microbiome (also called gut flora) is closely linked to our feelings of well-being & energy and could undergo positive changes during repeated periods of prolonged fasting. According to scientific evidence (Wang & al., 2021), interesting results have been observed in people practicing intermittent fasting with regard to the remodeling of the intestinal flora. Observations like these lead us to believe that intermittent fasting may increase the diversity of the gut microbiome and aid in digestion.

Focus & attention

Also, this food approach can have benefits in terms of concentration and attention.

When you wake up, fasting in the morning, the levels of cortisol (stress hormone) are at their highest in the body. The reason is simple, having not received food for several hours, the body will try to provide energy sources to offer to the organs to ensure their functioning. However, cortisol is a so-called “catabolic” hormone capable of degrading the body's energy reserves stored in the liver, muscles and adipose tissue. As fasting is a situation of “stress” experienced by the body, cortisol levels remain high and can then increase levels of alertness and mental acuity for an extended period.

Limit late night excesses

In addition, it can be a good starting option for people who have difficulty "controlling" their food intake. Indeed, by placing the individual within a certain food "structure", having a framework to follow can limit excesses and late-night snacking.

However, intermittent fasting also has its less "glamorous" sides... And a flip side to consider.

Loss of control

Deprived of food for a very long period, many lose control of the quality and/or quantity of food when it comes time for the first meal. Indeed, the emotional and impulsive sides can often take over at this time.

Decreased daily energy expenditure

Also, in the context of a weight loss goal, intermittent fasting is not necessarily a guarantee of success. During the fasting period extending over several hours, energy may be lower and the individual less inclined to move. Indeed, according to a 2021 study (Farooq & al.), people who adopted intermittent fasting as a dietary approach had a significantly lower daily energy expenditure than those with the same food intake spread over the day.

Risks of hypoglycemia

The "deprivation" of food for a prolonged period is certainly likely to lower the levels of "blood sugar" and induce hypoglycemia which can alter the proper functioning of the systems. If a significant decrease in blood sugar can have negative impacts in healthy individuals, they are all the more considerable in a population naturally more at risk such as diabetics and the elderly. Tremors, confusion, headaches, dizziness, anxiety, mood swings, weakness & loss of consciousness may be symptoms experienced.

Loss of muscle mass / performance

With the decrease in blood sugar induced by exercise or by prolonged absence of food, the body will try to find a way to rebalance blood glucose levels in order to ensure the maintenance of organ function. However, "gluconeogenesis" is the body's ability to create "new" glucose from proteins and contractile tissue present in the muscles. Such a dietary approach can therefore be counterproductive for individuals aiming to optimize their performance & maintain good muscle mass. In this regard, the scientific literature offers interesting evidence (Williamson & Moore, 2021). Intermittent fasting is said to be deleterious to sports performance & represents a sub-optimal dietary approach to maintaining or gaining muscle mass.

Risks of nutritional deficiencies

By eating within a certain 'window of time', the total number of meals in a day is often reduced and can therefore limit the intake of nutritious, quality foods. This phenomenon can put the individual at risk of having several deficiencies in vitamins & minerals as well as in important macronutrients such as proteins. The long-term impact of such nutritional deficiencies can negatively affect proper functioning of the hormonal system, maintenance of muscle mass, proper stress management, sleep & even daily energy levels.

Why is intermittent fasting interesting?

  • If you are a person who is not hungry in the morning
  • If you are a person requiring increased concentration in the morning
  • If you are a person in a highly cognitive job
  • If you are a person who tends to snack in the evening
  • If you frequently experience intestinal discomfort / bloating


Why would intermittent fasting be unattractive?

(x) If used as a primary means of losing weight/fat mass

(x) If your goal is to tone your muscles / gain muscle mass

(x) If your goal is to improve your physical or athletic performance

(x) If you suffer OR are at risk of suffering from an eating disorder

(x) If you are diabetic & taking medication that may cause hypoglycaemia


The scientific literature surrounding intermittent fasting looks promising. Although the evidence seems to show interesting effects in the context of weight loss, this approach would not have a greater effect than that which could be obtained with a more standard calorie deficit or better management of the energy balance ( calorie intake vs. calorie expenditure). In a systematic review (Ezzati, 2023), for a similar daily caloric intake, intermittent fasting would provide the same results on weight loss. In addition, the same observation is made with regard to the benefits on health markers and the prevention / control of chronic & metabolic diseases (diabetes, hypertension, cardiovascular diseases, cancer, etc.).

However, for some people, it may be easier to impose a "food window" according to a limited time slot to reduce the amount of calories ingested daily. For people who are not hungry in the morning or those who tend to "snack" in the evening, the results can be interesting.

However, in this way, we can miss an essential aspect to consider, “ food education ”:

Learn to eat well & choose the right foods according to our life context, our goals and the time of day. Such knowledge is not negligible since it will very well allow you to achieve a calorie deficit without having the impression of "depriving yourself" or eating according to a certain "schedule".

This food approach has its "pros" & its "cons", the important thing is to be aware of it and to be able to make an informed decision regarding its adoption in our daily lifestyle.

On these words, nothing prevents us from making a compromise and adjusting the underlying principles in our own way:

Achieve a caloric deficit through a natural, balanced & controlled daily diet, but choose to apply the concepts of intermittent fasting periodically & occasionally in order to gain some of its interesting aspects.

Hoping that everything has been able to enlighten you a little better on the subject!

The Purchasing Health team tells you: See you next blog ;)!


Abdelrahim, D., Faris, ME, Hassanein, M., Shakir, AZ, Yusuf, AM, Almeneessier, AS, & BaHammam, AS (2021). Impact of Ramadan Diurnal Intermittent Fasting on Hypoglycemic Events in Patients With Type 2 Diabetes: A Systematic Review of Randomized Controlled Trials and Observational Studies. Frontiers in Endocrinology, 12. https://doi.org/10.3389/fendo.2021.624423

Ezzati, A., Rosenkranz, SK, Phelan, J., & Logan, C. (2023). The Effects of Isocaloric Intermittent Fasting vs Daily Caloric Restriction on Weight Loss and Metabolic Risk Factors for Noncommunicable Chronic Diseases: A Systematic Review of Randomized Controlled or Comparative Trials. Journal of the Academy of Nutrition and Dietetics , 123 (2), 318-329.e1. https://doi.org/10.1016/j.jand.2022.09.013

Farooq, A., Chamari, K., Sayegh, S., El Akoum, M., & Al-Mohannadi, AS (2021). Ramadan daily intermittent fasting objectively reduces assessed habitual physical activity among adults. BMC Public Health, 21(1). https://doi.org/10.1186/s12889-021-11961-9

Su, J., Wang, Y., Zhang, X., Ma, M., Xie, Z., Pan, Q., Ma, Z., & Peppelenbosch, MP (2021). Remodeling of the gut microbiome during Ramadan-associated intermittent fasting. The American Journal of Clinical Nutrition , 113 (5), 1332–1342. https://doi.org/10.1093/ajcn/nqaa388

Williamson, E., & Moore, DR (2021). A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass? Frontiers in Nutrition, 8. https://doi.org/10.3389/fnut.2021.640621

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