• English
  • العربية
  • 中文
  • Français
  • Русский
  • Español

You are here

Nuclear Technique Provides Data to Define Four Phases of Metabolism in 'Landmark' Study


A nuclear technique and its resulting collective data have dispelled longstanding beliefs about metabolism – the chemical processes the body uses to produce energy. According to a study published in the journal Science earlier this month, prominent stages of life, like puberty, pregnancy and menopause, as well as gender and mid-life aging, do not affect metabolism as much as many believe.

The results of the study showed that metabolism can be divided into four life phases:

  • Up to 1 year of age: Metabolism is highest, about 50 per cent higher than for adults.
  • 1 – 20 years of age: Metabolism slows by 3 per cent each year.
  • 20 – 60 years of age: Metabolism stays stable.
  • After 60 years of age: Metabolism slows by about 1 per cent each year.

“Many of our beliefs surrounding metabolism were based on studies with limited data, and assumptions were made based on the little information we had,” said Alexia Alford, Nutrition Specialist at the IAEA’s Division of Human Health. “This is a landmark study for the IAEA and demonstrates how the application of isotopic and nuclear techniques are vital to understanding human health.”

The study illustrates how metabolism changes from birth to the ninth decade of life. "We know now, for example, that metabolism doesn’t slow in middle age, and women and men do not have different metabolisms,” Alford said. “The study also highlights the importance of the first year of life for development, when the high energy expenditure is due to the increased energy demand of growth and development.”

The data for the study was derived using a stable isotope technique, known as the doubly labelled water (DLW) method (see THE SCIENCE), and was gathered from the IAEA’s DLW Database, launched in 2018, which provided experts with the data of 6 421 people from 29 countries, aged eight days to 95 years. The technique is non-disruptive – individuals taking part in studies can go about their daily lives during the measurement period.

Experts evaluated the effects of age, body composition (the proportion of fat and fat-free mass) and gender on total energy expenditure or the number of calories burned. “The findings will help scientists better understand important questions about metabolic health and how to help people live healthier lives at every life stage,” Alford said.

The DLW Database

The IAEA DLW Database contains over 7 600 measurements collected from 128 studies between 1981 and 2019. Though most of the data submissions are from high-income countries, the database includes data from 32 countries in total. A coordinated research project will be launched later this year to support more low- and middle-income countries to implement the DLW method. Data submission to the IAEA DLW Database is encouraged.

“By bringing together the smaller studies of hundreds of different researchers from across the world in the IAEA DLW database, we have been able to compile the first complete picture of how metabolism changes through the life course,” said John Speakman, professor at the Chinese Academy of Sciences and University of Aberdeen, chair of the IAEA DLW Database Management Group and corresponding author of the recent study.

Cornelia Loechl, Head of the IAEA’s Nutritional and Health-related Environmental Studies Section, added: “By pooling data from different studies, it gives us the opportunity to do more powerful investigations and answer bigger questions.”

The DLW database was launched during the International Symposium on the Double Burden of Malnutrition for Effective Interventions in December 2018. Since its launch, 10 articles based on its data have been accepted or submitted for publication by other peer-reviewed journals.

Stay in touch