On innovative approach was used in the study to evaluate the relative contributions of food and exercise levels to the development of obesity.
The researchers employed a combination of methods like metabolic relationships, the laws of thermodynamics, epidemiological data and agricultural data, to reach the conclusions.
Lead researcher Professor Boyd Swinburn, chair of population health and director of the World Health Organization Collaborating Centre for Obesity Prevention at Deakin University in Australia, said the study demonstrated that the weight gained by American population seemed to be explained by that fact that there was more in-take of calories. It appeared that changes in physical activity played a minimal role.
Study details
The researchers tested 1,399 adults and 963 children to measure the total number of calories they could burn in real-life situations.
After this, Swinburn and his colleagues computed amount of food adults needed to eat so as to retain a stable body weight, and how much children needed to consume for normal growth.
In the next step, the study researchers determined the amount of food Americans were actually eating under free-living conditions.
For this, the researchers used national food supply data (the amount of food produced and imported, minus the amount exported, thrown away and used for animals or other non-human uses) from the 1970s till the early 2000s.
The researchers used these findings to predict approximate weight Americans would have gained over the 30-year period.
To find out the actual weight gained by Americans over that period, the researchers used data from NHANES (National Health and Nutrition Examination Survey), a survey research program conducted in the United States, that recorded the weight of Americans in the 1970s and early 2000s.
Study assumptions
Swinburn said "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."
"If the actual weight gain was higher than predicted, that would suggest that a decrease in physical activity played a role," he added.
Study findings
The study researchers deduced that rise in obesity in the United States was an outcome of over-eating since the 1970s.
It was found that the predicted and actual weight increase matched exactly in case of children, which implied that over-eating was responsible for the weight increase.
Swinburn concluded, "For adults, we predicted that they would be 10.8 kg heavier, but in fact they were 8.6 kg heavier. That suggests that excess food intake still explains the weight gain, but that there may have been increases in physical activity over the 30 years that have blunted what would otherwise have been a higher weight gain."
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