Are genes or the environment the main cause of obesity?
3 October 2012
The ongoing obesity epidemic is creating an unprecedented
challenge for healthcare systems around the world, but what determines
who gets fat? Two experts debate the issue on bmj.com.
Timothy Frayling, Professor of Human Genetics at the University
of Exeter thinks that genetic factors are the main driver for
obesity in today’s environment. Twin and adoption studies show
consistently that variation in body mass index has a strong genetic
component, with estimated effects of up to 70%, he says.
Studies also show that people carrying two copies of a gene
associated with obesity (the FTO gene) are, on average, heavier than
those carrying two copies of the protective version.
A recent study of over 200,000 people showed that the FTO variant
had a stronger effect in sedentary people than in those who are
physically active, while studies of physical activity in
schoolchildren suggest that education may not be as important as we
think, he adds.
“Although DNA variations explain only a small percentage of the
variation in body mass index, they provide proof of principle that
genetic factors influence it over environmental factors,” writes
In conclusion, he says, genetic factors influence substantially
where you are on the body mass index scale in a given population at
a given time, and evidence is accumulating that these genetic
factors may operate largely through appetite control.
He adds: “If true, plans based on changing our environment, such
as banning the sale of supersized sugary drinks, may be more
successful than plans to increase awareness through education.”
But John Wilding, Professor of Medicine at the University of
Liverpool believes that changes in our environment are responsible
for increasing obesity.
He acknowledges the role of genetics in the regulation of body
weight, but argues that the rapid increase in obesity seen over the
past 30 years cannot be due to genetic changes.
In contrast, the evidence that the environment has changed is
overwhelming, he says.
He points to the recent fall in the cost of energy dense foods,
alongside successful promotion by the food industry, and a decline
in physical activity due to changes in transport, technology, and
the built environment as key drivers for the obesity epidemic.
It will be important to identify genetic causes for rare cases
that may be treated, he says. However, changes to the food and
physical environment are going to be essential if we are to have a
meaningful impact on the obesity epidemic.
He calls for “a radical approach … backed by strong legislation
influencing food production and marketing, and ensuring the built
environment and transport systems are designed to encourage active
In summary, he says “obesity is a complex disorder with both
genetic and environmental causes. The predominant driver is
environmental, and changes to the environment will be essential if
we are to tackle the current epidemic.”
The article is available at: