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Age slows down... metabolism?

Updated: Jan 23, 2023

age metabolism

Of course, everyone knows it, it's already a consensus, isn't it? This is why the older you get, the more weight you gain and the harder it is to lose it.

...Or maybe not?

To be able to answer this question, we must first establish what is meant by "metabolism". The definition found in the dictionary is: "All the complex and incessant processes of transformation of matter and energy by the cell or the organism, during the phenomena of organic construction and degradation (anabolism and catabolism)."

But that doesn't make it any clearer. Already, if you managed to read it until the end, congratulations!

What we want to know is what the metabolism actually consists of, and how we quantify it, so that we can then know what "slowing down" means.

We can summarize the definition by: a series of processes of transformation of energy for the different needs of the organism.

So what are these processes and what are these needs?

  • In the first place: the need to live, therefore to function of all the organs. This is called basal metabolism.

  • Second, the need to perform all our daily activities: getting around, working, playing, doing household chores, etc. All of this is called non-exercise activity thermogenesis.

  • Then, we expend energy to digest and metabolize the food we eat, which makes up the thermic effect of food.

  • Finally, there is the energy that we expend when we do physical exercise, called exercise energy expenditure.

But how much does each of these contribute to total metabolism?

Visually, the distribution can be represented like this:


Note: Energy is measured in kilocalories (kcal), so metabolism will have a value measured in kcal/day, specific to each individual and slightly different from day to day, depending on the energy expenditure of each of its components.

"Sport does not make you lose weight", it is not a myth!

We notice that the basal metabolism occupies the largest part of our energy expenditure. What is perhaps more surprising is the energy expended in our daily lives, aka non-exercise activity; and especially in relation to the exercise energy expenditure ("sport does not make you lose weight", it is not a myth!).

So how would age impact each of the four processes described above?

Seeing the significant proportion taken by the basal metabolism compared to the others, one can easily suppose that it is this one the culprit, in other words that it is he who would slow down with age and which would make us put on weight.

A study was conducted worldwide (80 scientists, 63 institutions, 16 countries and 4 continents) on 6600 people of all ages to follow the evolution of basal metabolism during our lifetime. Published in 2021 in the prestigious magazine Science, this study determined the existence of four phases:

  1. The neonatal phase: up to 1 year

  2. The juvenile phase: between 1 and 20 years old

  3. The adulthood phase: between 20 and 60 years old

  4. The older phase: after 60 years

Their evolution is as follows:

BMR phases

Let's focus on the two phases that interest us: the adult phase and the older phase. We clearly see that the basal metabolism remains stable throughout our adult life, including during pregnancy and menopause!

There is also a slowing down of the metabolism from the age of 60, but this does not exceed 0.7% per year. We might as well conclude that it is not this decrease that makes us gain a few pounds once we retire! 😏

So if it's not the basal metabolic rate, who's to blame?

We still have 3 other components of the metabolism to analyze:

  • The thermic effect of food: this is proportional to the quantity and the caloric load of the food consumed and does not depend in any way on age. So if there is a change, it will be an increase more than anything else. (We surely consume more calories at the age of 50 than at 20... 😉)

  • The exercise energy expenditure: do we practice physical exercise as regularly when we have a family life as when we were in school? Generally not, and in the end it contributes very little in the total metabolism (5-10%) to make a real difference, you will tell me.

  • Non-exercise activity: do we move less at 50 than at 20 years old?

Could it be the daily activity (the 2nd most contributing element to total metabolism) that needs to be put into question?

Surely: we benefit from more comfort (we might use the car more than the public transport), we have a sedentary job, we may even have automated or delegated household chores, and the list can go on. With a little retrospection, we can most likely all see that we are moving less than 20 years ago.

And even if there is no need for scientific research to confirm it, this prospective study from 2013 followed 519 people for 6 years and determined a decrease in daily activity of 3% more each year. This means that at the age of 91 the activity decreases 2 times faster compared to the starting base than at 71! In my opinion, since 2013, the situation must have gotten even worse in terms of sedentary lifestyle.

But this is obviously not intrinsic to age. It is a byproduct of our actions, our priorities, our (pre)occupations, which change throughout our lives.

Finally, let's not forget that the answer of weight gain or weight loss is always found on both sides of the energy balance: expenditure (the total metabolism) AND consumption. And it is very likely that we eat more and more calories during our professional life than when we were still in school.

"We are not victims of our metabolism, but of our lifestyle."

So, if there is one element that age slows down, it's us, it's not the metabolism!

With age we slow down, we always seek more comfort, we are more sedentary and we do less physical exercise. We are not victims of our metabolism, but of our lifestyle.

But this is actually very good news! This means that gaining weight as you age is not a fatality, and it's completely preventable because it's in our power. And even if it has already happened, it is completely reversible by the same means, with adequate lifestyle changes.

How do you know if you are on the right track in terms of sedentarism or how to reverse the trend? My dedicated article sheds light on this subject and offers you simple and effective ways to achieve this.

Do you want to go further? Do you need specialized coaching to get there? Contact me and you will no longer be alone!

To quote the writer Jules Renard: "It's not how old you are, it's how you are old."

If you want to discuss on the subject and not miss any news, follow my Facebook or Instagram page. See you soon ! 👋


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