Increased Food Intake Alone Explains Rise In Obesity In United States, Study Finds
research that uses an innovative approach to study, for the first time,
the relative contributions of food and exercise habits to the
development of the obesity epidemic has concluded that the rise in
obesity in the United States since the 1970s was virtually all due to
increased energy intake.
much of the obesity epidemic has been caused by excess calorie intake
and how much by reductions in physical activity has been long debated
and while experts agree that making it easier for people to eat less
and exercise more are both important for combating it, they debate
where the public health focus should be.
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.
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.
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.
they had determined each person's calorie burning rate, Swinburn and
his colleagues were able to calculate how much adults needed to eat in
order to maintain a stable weight and how much children needed to eat
in order to maintain a normal growth curve.
then worked out how much Americans were actually eating, using 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 and the early 2000s.
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. They used data from a nationally
representative survey that recorded the weight of Americans in the
1970s and early 2000s to determine the actual weight gain over that
the actual weight increase was the same as what we predicted, that
meant that food intake wasvirtually 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."
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
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," Swinburn said.
return to the average weights of the 1970s, we would need to reverse
the increased food intake of about 350 calories a day for children
(about one can of fizzy drink and a small portion of French fries) and
500 calories a day for adults (about one large hamburger)," Swinburn
said. "Alternatively, we could achieve similar results by increasing
physical activity by about 150 minutes a day of extra walking for
children and 110 minutes for adults, but realistically, although a
combination of both is needed, the focus would have to be on reducing
emphasized that 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.
For more information on the European Association for the Study of Obesity, visit www.easo.org.