A group of experts and scientists from the International Atomic Energy Agency has concluded that total human energy expenditure has decreased in both men and women in the last 30 years. Contrary to what was expected, the researchers discovered that it is not due to the reduction in physical activity expenditure, but rather to the decrease in basal expenditure.
Basal expenditure is the energy used for basic bodily functions, such as respiration and circulation. This expenditure, combined with that used for day-to-day activities, make up the total energy expenditure.
The results help understand how food intake contributes to obesity, a condition that can decrease the quality of life and contribute to the appearance of various diseases. Already considered an epidemic that grows every day, it occurs when energy intake is greater than a person’s energy expenditure.
According to the authors, until now it had been assumed that obesity was caused by increasingly sedentary lifestyles, in which physical activity has decreased considerably and, on the contrary, food intake has increased.
Dual labeled water
The document has been prepared from the database Dual labeled water of the Agency, created in 2018, which provides a data repository that includes information on the participants, their age, body composition and activity levels.
To collect the data, scientists use water that contains two stable isotopes, hydrogen-2 and oxygen-18, to determine how much energy a person has expended, or in other words, how many calories they have burned.
Each participant consumes a double labeled dose of water before resuming their normal activities. Urine samples are then collected over a period of 10 to 14 days to determine how quickly the two isotopes leave the body. Calculating the rate at which these isotopes are removed, one can estimate the amount of carbon dioxide produceda figure that is related to energy expenditure.
For the recent work, measurements collected since the 1980s on the energy expenditure of more than 4,500 adults in Europe and the United States were analyzed, allowing the researchers to discover that the total energy expenditure has decreased since the 1990s around 7.7% in men and 5.6% in women.
John Speakman, lead author of the study and a professor at the Shenzhen Institute of Advanced Technology in China and the University of Aberdeen in the UK, said activity spending has risen slightly over time. “What really has decreased is the basal energy expenditure. This means that the resting metabolic rate of a person living in 2023 is lower than that of a person of their same age and body composition in the late 1990s. That’s pretty unexpected. And we don’t really know why.”
Speakman added that there are several potential factors that may explain why basal energy expenditure has decreased, including dietary changes. However, they need more research to understand how to reverse this decline. “This could be the basis of a useful strategy in the treatment of obesity. However, at present, the best way to avoid it is not to overeat.”
Extend the investigation
The database contains more than 8,000 measurements from 37 countries made with its method since 1981. Since the figures come mostly from research carried out in Western countries, the Agency has begun a investigation project coordinated project started this year, with the aim of add information from Asia, Africa and Latin America.
“These data have allowed us to better understand the obesity epidemic and have provided, for the first time, evidence on how energy expenditure has decreased in the last 30 years,” said the head of the section of Nutritional and Environmental Studies Related to Health at the Organization and co-author of the document.
Cornelia Loechl added that “individual studies are often small and not generalizable. However, when combined into one database, big questions about the causes of obesity can be addressed.”