Food is always a subject of choice for our books in Quebec and for our health. It is a source of comfort, pleasure and nutrition (or not). But what about the subject of fasting? The pleasure of not eating? The benefits of having no nutritional intake? It does not bring comfort, it would even increase stress and anxiety (and it is very logical, I will come back to this).

I will talk about it in a series of articles which aim to demystify what fasting is, the reasons for considering it and especially the benefits and risks of this approach for overall health. As usual, I will take this opportunity to establish the basics of biology related to this subject in order to fully understand the issues and impacts from a physiological point of view.

First, a word about calorie intake. During evolution, it is obvious that humans did not eat three meals a day in addition to two snacks. We have evolved for thousands of years with the daily goal of finding food to survive. We just have to think of the TV shows that have wilderness specialists for forest survival, who are left for 3 weeks, with only a knife and a container for cooking. They usually lose 10 to 15 pounds because they are unable to eat enough. Thus, the human being has surely not evolved in abundance. Please note, we had a life expectancy of 25 to 35 years in this primitive era. So that doesn’t mean that what we were able to do was the best for our health. What I’m getting at is that there are many, very well documented benefits of calorie restriction or fasting and that in humans, these benefits would be inducible over relatively short periods of time, possibly due to our evolution. This is a very important aspect to fully understand the benefits of fasting, we will come back to this.

We have already published an article explaining what calorie restriction is, (Healthy Aging (Article 2): caloric restriction). In my 4th book, which has just been published, written with the collaboration of 7 other health professionals, I also talk about the “Longevity Diet”. This is the title of a book written by a great researcher in the field of aging, director of two very high-level research centers, Valter Longo. Fasting should be seen as a food mode that is one of the possible tools for healthy eating.

Secondly, fasting makes sense from a biological point of view when one learns about inducible mechanisms and their metabolic roles. Here some will say “yes, but we are told that we must eat three meals a day and snacks, we no longer know who to believe”. Indeed, the dietary recommendations are changing and although we have been talking about the benefits of fasting for more than 30 years in the scientific literature, what made me to talk about it is a recent article published in the “New England Journal of Medicine” (de Cabo and Mattson, 2019). It is one of the most prestigious and respected scientific journals for the quality of these publications. In summary, the article in question mentions (in my paraphrasing):

“There is mounting evidence that eating over a 6-hour period and fasting for 18 hours can cause a metabolic change from switching from glucose to using ketones as an energy source, with improved resistance mechanisms, better longevity and reduced incidence of diseases including cancer and obesity.”

The authors of this scientific article are two specialists in the matter. They emphasize here that it is not necessary to fast for 3 days or 3 weeks to have the benefits. As previously mentioned, the mechanisms responsible for the benefits are inducible over short periods. This means that over an 18 hour period without eating, the body will already begin the entire protective process necessary to get through a period of fasting. These mechanisms, which are very beneficial for health, can therefore be induced or stimulated, depending on the frequency of our diet.

Let’s finish by mentioning that this is completely normal. As mentioned, humans have certainly not evolved by eating three meals a day and two snacks (which is justifiable for growing children or some elderly at risk of undernutrition).

For our ancestors, the cavemen, they probably began each day with a new quest in finding ways to feed themselves and those closest to them (as in the Croods (a cartoon that I love)). It is therefore normal to have periods without eating and it would be very beneficial for health to be hungry and to resist it.

In the next articles I will explain to you why and especially how to make the most of it.



  • Longo et Mattson, 2015. Fasting: Molecular Mechanisms and Clinical Applications. Cell Metab. Author manuscript; available in PMC 2015 Feb 4. Cell Metab. 2014 Feb 4; 19(2): 181–192.
  • Mattson, Longo, et Michelle, 2017. Harvie Impact of Intermittent Fasting on Health and Disease Processes. Ageing Res Rev. 2017 October ; 39: 46–58.
  • de Cabo et Mattson, 2019. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medecin. 381 (26), 2541-2551. 2019 Dec 26.