New study links unexpected factor to obesity epidemic.

New Study Reveals Decrease in Basal Metabolic Rate May Contribute to Obesity Epidemic

What is Basal Metabolic Rate?

Basal metabolic rate (BMR) is the number of calories the body burns while at rest. It is the energy required per unit of time for the body to maintain vital functions such as breathing, blood circulation, and maintaining body temperature. BMR is one component in the body’s total energy expenditure, the other being activity expenditure, the number of calories burned during physical activity, such as running or walking.

The Study

A new study published in Nature Metabolism (pdf) has revealed that the BMR in people in the United States and Europe has decreased over the past three decades, potentially contributing to the growing obesity epidemic in both regions. The study analyzed data from nearly 4,800 adults in Europe and the United States from the late 1980s to the present day. The data indicated a decline of approximately 7.7 percent in men and 5.6 percent in women in adjusted total daily energy expenditure since the 1990s. In terms of adjusted basal energy expenditure, men experienced a drop of 14.7 percent over time, while women’s decline was 2 percent and not deemed significant. However, a larger dataset of BMR measurements of nearly 10,000 adults across 163 studies going back 100 years confirms the decline in both men and women.

Why Has Basal Metabolic Rate Been Declining for Decades?

One factor that may be important in explaining the decline is food. “Diets have changed enormously over the past 100 years,” said John Speakman, a professor at the Chinese Academy of Sciences in Shenzhen, China, and a lead author of the study. The authors of the study pointed out that over the 20th century, people’s diets underwent numerous changes, including the amounts and types of carbohydrates, fiber, and fats consumed. For example, in 1910, animal fats accounted for over 90 percent of the fat intake, but currently, they account for less than 15 percent. Researchers conducted experiments on mice to explore the possible impact of these dietary changes, allowing for well-controlled and monitored diets. The results suggested that intake of saturated fats could be an essential factor in lower basal energy expenditure. These findings could indicate that our dietary shift from predominantly animal-based to plant-based fats over the past century may have contributed to the decline in energy expenditure, affecting our metabolic rate and thus making obesity more likely.

Other Possible Factors for the Decrease in Metabolic Rate

Exposure to environmental chemicals and unhealthy lifestyle behaviors are the two main reasons for the global sperm count drop, according to Dr. Shanna Swan, one of the world’s leading environmental and reproductive epidemiologists and an author of the study on sperm. Mitochondria, the tiny organs within a cell, play a central role in energy metabolism by converting energy from food into a form the body can use. Something in our environment is poisoning our mitochondria, said Dr. Christopher Palmer, an assistant professor of psychiatry at Harvard Medical School specializing in the connection between metabolism and mental health.

How to Speed Up Metabolism

Discovering why metabolism slows down is a “complex phenomenon,” said Dr. Konstantinos Spaniolas, director of the Bariatric and Metabolic Weight Loss Center at Stony Brook University. However, increasing physical activity is one way to improve metabolic profile, and balanced, whole-food diets can increase metabolism. Improving metabolism may also involve adequate sleep, stress management, and nutrient supplementation.

Study Limitations

The study’s authors acknowledged that one of the main limitations is its cross-sectional design, which does not allow for establishing a causal link between changes in metabolic rate and the changes in obesity rates. Furthermore, despite adjusting the basal energy expenditure for age and body composition, other factors may need to be considered. The study’s participants may not have been representative of the underlying population, and a long-term decrease in BMR may have come from methodological factors.