Through a study of 6,500 participants between the ages of 8 days and 95 years that analyzed how their bodies burn energy over a period of more than 40 years, an international team identified 4 periods of human life and debunked many myths about metabolism.

slowed metabolism

In a report published by the French newspaper "Le Monde", author Florence Rosier said that a study published in the "Science" magazine on 6421 people between the ages of 8 days and 95 years, 64% of whom were women, from 29 countries, revealed many surprises.

Many people think that puberty, thirties or forties and menopause are periods when metabolism slows, but this is not true.

Dr Hermann Pontzer from Duke University in the United States of America, first author of this international study coordinated by John Speakman from the University of Aberdeen, UK, says that this "may seem strange, but the division of different metabolic periods by age does not match with The major life stages mentioned.

Researchers used a "double-label water" technique to measure how the body burns energy daily (Shutterstock)

double label water

The researchers used a reliable, accurate, non-invasive reference technique that has been in use since the 1980s to measure how the body burns energy daily, and it is known as "double-label water".

The principle of this method is for a person to swallow a dose of water that contains two stable isotopes, deuterium (2H) and oxygen (18O).

By analyzing urine samples taken regularly over a period of 1 to 3 weeks, it is measured how these two isotopes are metabolized in the body.

This technique allows calculating the amount of carbon dioxide produced by the body, from which the rate of burning energy is calculated.

However, this method requires follow-up and mass spectrometric analyzes that are time consuming and expensive.

Hence the benefit of collecting data by 6 laboratories over the past 40 years.

Children burn 50% more energy than adults (Shutterstock)

Babies burn a lot of energy

The analysis model for children consists of 4 stages, based on data on body mass without fat.

First, early childhood. Young children show maximum energy expenditure, the rate rising during the first year of life.

Between the ages of nine and 13, children burn 50 percent more energy than adults, based on body mass without fat.

The question arises: Is this due to the fact that children triple their birth weight during the first year of their life?

Dr. Pontzer notes that "some processes that occur at the cellular level make the child's body more active, and we do not know their nature."

Perhaps this dense metabolism partly explains why, during this key period, nutrient deficiencies cause severe and potentially life-threatening growth disturbances.

After one year of age, the level of metabolism slowly decreases by 3% per year until the age of 20.

The surprise is that even puberty, which is characterized by hormonal disruptions and a growth spurt, does not affect the slowing down of the metabolism.

During this period, the body's energy needs continue to decrease with regard to body size.

This shift was observed even among students between the ages of 18 and 20 years.

Sedentary lifestyle or unhealthy diet are factors that lead to fat accumulation (Shutterstock)

Lifestyle and diet

Weight gain is often thought of as inevitable from the age of 30 onwards, and it is wrong to "blame metabolism".

There is no doubt that a sedentary lifestyle or an unhealthy diet is one of the factors that lead to the accumulation of fat around the waist circumference in your thirties or forties.

In fact, metabolism has nothing to do with weight gain because for 4 decades, from the age of 20 to 60, the level of energy expenditure is remarkably stable.

Even pregnancy does not affect the woman's body's energy needs, taking into account the increased weight of the fetus.

For a young person weighing 40 kg, the maximum energy expenditure is about 10 megajoules per day, of which 50% to 70% is metabolized during periods of rest.

Metabolic levels vary from person to person, and some people show energy burning levels that are 25% higher than their average age, while others are 25% lower.

However, this 4-stage model remains valid when individual levels of physical activity are taken into account.

After the age of 60, cell activity slows down and the metabolic level begins to decline by 0.7% per year.

The loss of muscle mass partly explains this slow decline, as muscle burns more calories than fat tissue.