Written by Pierre MARSANT


Weight loss: what no one has ever told you!

Every year, we see new food trends appear that are more or less questionable from a physiological point of view. We hear everything and its opposite about so-called miracle diets, superfoods, etc… with variable geometry effects in terms of results.

Sports will you tell me?

Although essential for a good metabolic balance, physical activity does NOT lead to weight loss. You will be surprised to learn that you probably lose more weight during a good night's sleep than during 2 hours of physical activity.

But if everyone only talks to you about controlling your energy intake, in this article we will talk about optimizing your expenses!

So what is the real driver of weight loss?

1) A few reminders... 🧪 ⚛️

a) Cocorico!

In his Elementary Treatise on Chemistry , Antoine Lavoisier essentially proves that during chemical interactions between different bodies:

“Nothing is lost, nothing is created, everything is transformed”

This will result in an elementary principle of modern physics: the principle of conservation of mass.

This discovery totally demystifies chemistry and constitutes one of the first demonstrations that it is possible to quantify matter precisely, atom by atom.

This notion will be very useful to us later 🙂

b) Another story of oxygen and carbon..

These elements constitute respectively 65 and 18% of our weight.

They interact together during a chemical reaction at the base of Life: Cellular Respiration.

During this reaction, carbon is the element that is “burned”, it is directly or indirectly provided by food. It is carried by the nutrients (carbohydrates, proteins, lipids) which are the fuel of our cells.

A direct intake means that the carbon-carrying nutrient (example: glucose) circulates in the system following a recent dietary intake.

An indirect contribution, is characterized by the contribution of these nutrients following the metabolization of our “reserves”. They are scattered everywhere and are mainly stored in our muscles and our beloved "fat" tissue.

Oxygen is the “burning” element, it comes from the air we breathe. It is continuously present in our lungs where it is absorbed into the blood.

The elements resulting from this reaction are CO2 and heat.

If we apply Lavoisier's principle of conservation of mass, it is important to emphasize that the mass (and therefore the weight) of the system remains unchanged as long as the CO2 is not eliminated. Heat is just energy and has no mass in itself.

Respiration is essential both for the supply of oxygen necessary for the reaction as well as for the elimination of CO2.

The respiratory volume is the key element to have a stable weight and to help you lose it.

2) Introduction to the concept of "Basic metabolism"

Basal metabolism or resting metabolism corresponds to the "incompressible" energy needs of the body . That is to say the minimum daily energy expenditure allowing the organism to survive.

It represents a daily consumption of 1500 kCal, which represents a non-negligible energy expenditure! and we know very well that if we expend energy; it's that we're eliminating carbon somewhere! ;)

So maintaining the basal (or resting) metabolism is of paramount importance in weight control.

But what are the factors that influence this basal metabolism?

- Age:

We therefore observe that this metabolism decreases inexorably in a manner almost proportional to the “aging” of the subject.

We can then emphasize the relevance of compensating for the decrease in basal metabolic rate with age by increasing physical activity or decreasing intake in order to guarantee a viable and healthy intake/expenditure balance.

- Physical inactivity :

“The Calorie Twins Hypothesis”

Let's take the example of 2 homozygous twins (identical twins).

Each is put in a fictitious room that does not let any heat escape. We could then measure the caloric energy emitted by each of the 2 subjects and thus deduce the energy expenditure.

Imagine that the 2 subjects are lying down for 24 hours:

One could then think that the energy expenditure of the 2 subjects would be strictly identical, in practice this is rather what it looks like:

Basal metabolism is not an exact science and other factors, often impalpable, come into play.

It can be concluded that over a given period, the total energy expenditure linked to basal metabolism tends towards the same value. In contrast, instantaneous energy expenditure tends to vary.

Suppose now that subject 1 continues to respect this constraint for 1 month, but that subject 2 practices 5 hours of regular physical activity per week with an exercise routine well defined in advance.

Defining the sequence of exercises in advance and repeating the same allows us to determine in advance the amount of energy expended specifically during exercise. (Ex: 1 hour of cycling approximately 580 Kcal) And thus, impute them to the total energy expenditure in order to precisely calculate the quantity of energy linked to resting metabolism only.

Here's what the monthly averages of basal metabolism should look like on the 2 subjects over 6 months:

We should therefore observe 2 things:

- A sedentary lifestyle leads to a decrease in basal metabolic rate over the long term.

-Physical activity, even practiced sporadically, makes it possible to maintain the basic metabolism at its nominal level, or even to strengthen it.

How to explain this evolution ?

The answer lies in our favorite tissue: muscle.

By building muscle, a big consumer of energy, you burn more calories, even at rest. This is why it is always advisable to build muscle when trying to lose weight since over the long term muscle allows you to consume additional energy.

On the contrary, restrictive diets; lead to a depletion of muscle mass, because it is used as an energy reserve, to the detriment of the basic metabolism.. and here is how to create the perfect one: Yo-Yo effect!


No miracles! Healthy and sustainable mechanisms are put in place over the long term.

The body is a “long distance runner” and sudden changes in diet or the volume of your physical activity are never a good idea.

Get advice from your coach or a nutritionist/dietician, while keeping in mind that patience and time are your allies!

“You should never do something with the aim of losing weight, you should rather ask yourself what you can do to help your body maintain its metabolism”