Fat storage: how does our metabolism change over the years?

[Article updated on 19/09/2023]

Generally speaking, the older we get and the more the metabolism slows down. After age 45, on average we estimate a loss of 10% of muscle mass every ten years. That amounts to losing 1/3 of our muscle mass per year and gaining as much in body fat. Since muscle mass spends more calories than body fat a drop in daily caloric needs are felt to maintain a fitness weight. It is therefore common for fat gain to occur is felt to the detriment of muscle mass. (Ex: the menopause in women is more revealing).

Before reading on

I’m not an expert in this field, but I am passionate about nutrition and health.

The articles you’ll find on my site are the result of in-depth research that I’d like to share with you. However, I would like to stress that I am not a health professional and that my advice should in no way replace that of a qualified physician. I’m here to guide you, but it’s important that you consult a professional for specific questions or medical concerns. Your well-being is important. So be sure to consult the appropriate experts and take the best possible care of yourself.

So what is metabolism, why does it vary and how to overcome this?

What is basal metabolism?

THE basic metabolism is specific to each individual, it corresponds to the energy necessary to keep our body active and perfectly functional. It is calculated based on our weight, our age, our height, our muscle mass, our gender, and the outside temperature (weather). Its unit is the Mega Joule (MJ) but it is often converted to kilocalories (or calories) for the general public. NB: 1 kilocalorie = 4.18 kjoules.

He is our benchmark for establishing a balance between expenses (energetic) and (energy) inputs.

Example : The needs of a woman (60kg) aged 20 to 40 with an activity usual are 2200 kcal on average. And the needs of a man (70kg) from 20 to 40 years old are 2700 kcal on average.

This one can evolve according to our energy expenditure daily. We have “hands” on the variations of it through this means. (Example: a hairdresser, who performs his journeys on foot to get to work will not have the same energy expenditure than an office worker sitting all day day and taking the car to go to work).

Example: The needs of a woman (60kg) aged 20 to 40 with usual activity are 2200 kcal on average BUT those of an inactive woman (60kg) of the same age are 1900 kcal. In the same way that the needs of a man (70kg) aged 20 to 40 are 2700 kcal on average BUT those of an inactive man (70kg) of the same age are 2400 kcal.

What is this metabolism for?

Let’s go from the principle that our basic metabolism is: 5.7 a 20 year old woman weighing 60 kg

This metabolism is multiplied by 1.6 because this young woman has a physical activity corresponding to seated work with small travel, a usual activity.

MB (basal metabolism)
NAP (physical activity level)
BE = Energy requirement (daily)

MB*NAP = BE i.e. 5.7*1.6 = 9.12 MJ/d

We we therefore achieve a daily energy requirement of: 9.12 Md/d i.e. 2200 kcal/day

THE form weight is representative of the balance of this scale (photo attached). The more balanced the scale, the more the diet is also and the healthier and healthier the body is good health. Weight gain or weight loss (too fast and involuntary) is a sign of a nutritional imbalance between need and contribution.

  • If this young woman provides more calories than she needs (2200 Kcal/day), in the long term there will be an increase in body fat (the body will store the excess energy provided)
  • If this young woman brings as many calories as she needs (2200 kcal/d) in the long term and therefore as much energy as that spent, there is no storage of fat mass. In conclusion, the weight remains stable.
  • If this young woman brings fewer calories than she needs (2200kcal) and therefore less energy than that spent in the long term, there will be a weightloss : fat mass (but also muscle mass if you do not practice physical activity to compensate for it).
Energy balance

Metabolism correlated with age.

Naturally, metabolism slows down with age. The main reason ? The level of hormones that decreases in our body. THE hormone levels are at their highest until the age of 20, because they remain essential to growth until then and for a maintenance until the age of 30

In a few figures: Our metabolism base falls by 2 to 3% every 10 years.

During aging, there is a decrease in mass lean and an increase in fat mass. For example : A man loses on average 12 kg of muscle between the ages of 20 and 75, with an increase in fat mass.

Here is two photos of John Turner, one American psychiatrist, (at 67 and 79 years) to illustrate this.

Photos provided by Professor Stéphane Schneider

John Turner

We can see other changes related to metabolism with aging:

  • Concerning lipid metabolism at the enzymatic level. Certain fatty acids need to be supplemented because they are no longer synthesized.
  • Insulin secretion also changes and could lead to insulin resistance. A high sugar level would remain in the blood. (diabetes)
  • The digestive absorption of calcium also loses efficiency. To be supplemented to avoid osteoporosis. (loss of bone mass, fractures, etc.)
  • A reduction in water mass: around 20% at age 60 (and loss of the feeling of thirst)

Other age-related causes

Sarcopenia (or age-related muscular dystrophy) is a pathology resulting from a progressive and high loss of muscle mass and function and some strength during aging. 25% of people over 70 and 40% of those over 80 are sarcopenic. To the hospital, sarcopenia affects 21 to 44% of people over 65 who are malnourished or at risk of being so.


This one is accentuated by:

  • A reduction in physical activity thus reducing muscle mass but also bone mass which is also a living tissue destined to decrease with age. All of which also becomes a cause and effect.
  • Teething problems (more difficult chewing), and therefore a distaste for meat which would reduce the proteins provided by the diet. And once again by cause and effect decreases muscle mass.
  • A dietary imbalance linked to a pathology (e.g. Alzheimer’s: forgetting meals or ingested foods, taking foods intended for snacking: more accessible, without the need to cook, etc.)

How to overcome the effects of age on metabolism?

He It is therefore important to maintain physical activity adapted to our age and our abilities to compensate for muscle wasting and bone.

And obviously, it is necessary to have a diet balanced, adapted to our expenses and our needs. Only the diversity of diet allows you to obtain a good balance of the main nutrients (proteins, lipids, carbohydrates) and ensures a correct intake of vitamins, minerals (iron, calcium, magnesium) and fiber.

For to do:

  • Maintain a good intake of proteins: rather lean meats, fish or eggs.
  • Maintain a good intake of calcium: dairy products (to limit bone loss)
  • Avoid foods that are too rich in sugar or salt: often too high in calories and uninteresting from a nutritional point of view. (pastries, candies, sweet biscuits, aperitif biscuits, etc.)
  • Favor a rich diet in vitamins, minerals with fresh fruits and vegetables. These contributions are essential for the proper functioning of the body and these Foods are very low in calories.

YOU you will have understood: we can therefore compensate for the slowing down this metabolism via physical activity, a healthy, balanced and adapted diet but also a healthy lifestyle.