Is metabolic rate of population slowing down?
According to a new study, the total daily energy expenditure of individuals has decreased due to a slowing metabolism, not reduced activity.
In this recent study, researchers analyzed high-quality data spanning the last 100 years and found that people’s metabolism is decreasing (by approximately 81 kcal/day over the past 100 years).
Why is this important?
Obesity is currently a major problem, and a slower metabolism may contribute to it. However, based on the measurement results, we cannot claim that the decrease in population metabolism is the sole cause of obesity. The primary reasons for obesity still remain the consumption of highly processed foods and our convenience in meal preparation.
The model assumed:
Increased activity expenditure measured by energy expenditure as total Energy Expenditure – TEF – BMR. It is assumed that 10% of energy from food is spent on digestion. These numbers are measured based on natural foods. Ultra-processed foods are more easily digestible, resulting in lower energy expenditure for digestion.
Increased body temperature as a sign of activity (In studies before 2021)
What could explain the decrease of BMR?
Raise in global temperature – warming up body costs energy;
More sterile environment. Immune system costs energy.
Change of diet from saturated to monounsaturated fats (Based on rat studies)
The take-home message:
! Contrary to the assumptions in the study, physical activity went down on population level,.
! Assumed TEF
! Even if the assumptions are correct, it doesn’t explain obesity.
Speakman, John R et al. “Total daily energy expenditure has declined over the past three decades due to declining basal expenditure, not reduced activity expenditure.” Nature metabolism vol. 5,4 (2023): 579-588. doi:10.1038/s42255-023-00782-2