A RECENT large-scale study has revealed for the first time what happens with a person’s metabolism throughout his or her life and how metabolic rates decrease later than previously thought, Shenzhen Economic Daily reported yesterday.

The study, published in the journal Science, was the result of work by international teams of scientists, including one led by John Roger Speakman, chief scientist at the Center for Energy Metabolism and Reproduction of Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences.

People often say, “I’m not burning those calories as quickly as I did when I was younger,” attributing those extra pounds gained in middle age to a slower metabolism.

However, the study has unexpectedly found that the rate at which humans burn calories is relatively stable from their 20s to their 50s. Metabolic rate begins to slowly decline by age 60 and beyond.

The study had researchers analyze the daily lives of over 6,000 people aged one week to 95 years old across 29 countries.

To calculate an individual’s energy expenditure, the researchers looked at data gathered using a method called “doubly labeled water.” The method, though expensive, is not new and has been used by researchers in humans since the 1980s.

The new study is the result of a massive international collaborative data-sharing effort. The study is also a broad investigation on human metabolism through the “doubly labeled water” metabolic data from individual small studies shared by scientists from all over the world.

According to the research data, energy expenditure rapidly increases from birth to the first 12 months, before peaking at the age of 1, with infants burning calories around 50 percent faster than adults.

After the initial increase in infancy, metabolism slows down by about 3 percent each year. Once metabolic activity stabilizes when the person hits his or her 20s it remains relatively constant until around the age of 60.

“Our research shows that middle-age spread may be related to pressure from family and society or eating habits, and the change in metabolic rate is not one of the reasons,” Speakman said.

According to the study, a person’s metabolism begins to gradually slow down after the age of 60, with energy expenditure declining at a rate of around 0.7 percent per year. A 90-year-old needs 26 percent fewer calories per day than a middle-aged person.  (Zhang Yu)