A study presented on Friday at the European Congress on Obesity is the first to examine the question of the proportional contributions to the obesity epidemic by combining metabolic relationships, the laws of thermodynamics, epidemiological data and agricultural data.
There have been a lot of assumptions that both reduced physical activity and increased energy intake have been major drivers of the obesity epidemic.
Until now, nobody has proposed how to quantify their relative contributions to the rise in obesity since the 1970s.
“This study demonstrates that the weight gain in the American population seems to be virtually all explained by eating more calories. It appears that changes in physical activity played a minimal role,” said the study’s leader, Professor Boyd Swinburn, chair of population health and director of the World Health Organization Collaborating Centre for Obesity Prevention at Deakin University in Australia.
The scientists started by testing 1,399 adults and 963 children to determine how many calories their bodies burn in total under free-living conditions. The test is the most accurate measure of total calorie burning in real-life situations.
The researchers used their findings to predict how much weight they would expect Americans to have gained over the 30-year period studied if food intake were the only influence.
“If the actual weight increase was the same as what we predicted, that meant that food intake was virtually entirely responsible. If it wasn’t, that meant changes in physical activity also played a role,” Swinburn said. “If the actual weight gain was higher than predicted, that would suggest that a decrease in physical activity played a role.”
The researchers found that in children, the predicted and actual weight increase matched exactly, indicating that the increases in energy intake alone over the 30 years studied could explain the weight increase.
Physical activity should not be ignored as a contributor to reducing obesity and should continue to be promoted because of its many other benefits, but that expectations regarding what can be achieved with exercise need to be lowered and public health policy shifted more toward encouraging people to eat less.
Source: European Association for the Study of Obesity, Netherlands