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| The Hadza live a hunter gatherer existence that has changed little in 10,000 years |
The idea
that exercise is more important than diet in the fight against obesity has been
contradicted by new research.
A study of
the Hadza tribe, who still exist as hunter gatherers, suggests the amount of
calories we need is a fixed human characteristic.
This
suggests Westerners are growing obese through over-eating rather than having
inactive lifestyles, say scientists.
One in 10
people will be obese by 2015.
And, nearly
one in three of the worldwide population is expected to be overweight,
according to figures from the World Health Organization.
The Western
lifestyle is thought to be largely to blame for the obesity
"epidemic".
Various
factors are involved, including processed foods high in sugar and fat, large
portion sizes, and a sedentary lifestyle where cars and machines do most of the
daily physical work.
The
relative balance of overeating to lack of exercise is a matter of debate,
however.
Some
experts have proposed that our need for calories has dropped drastically since
the industrial revolution, and this is a bigger risk factor for obesity than
changes in diet.
A study
published in the PLoS ONE journal tested the theory, by looking at energy
expenditure in the Hadza tribe of Tanzania.
The Hadza
people, who still live as hunter gatherers, were used as a model of the ancient
human lifestyle.
Members of
the 1,000-strong population hunt animals and forage for berries, roots and
fruit on foot, using bows, small axes, and digging sticks. They don't use
modern tools or guns.
A team of
scientists from the US, Tanzania and the UK, measured energy expenditure in 30
Hadza men and women aged between 18 and 75.
They found
physical activity levels were much higher in the Hadza men and women, but when
corrected for size and weight, their metabolic rate was no different to that of
Westerners.
Diverse
lifestyles
Dr Herman
Pontzer of the department of anthropology at Hunter College, New York, said
everyone had assumed that hunter gatherers would burn hundreds more calories a
day than adults in the US and Europe.
The data
came as a surprise, he said, highlighting the complexity of energy expenditure.
But he
stressed that physical exercise is nonetheless important for maintaining good
health.
"This
to me says that the big reason that Westerners are getting fat is because we
eat too much - it's not because we exercise too little," said Dr Pontzer.
"Being
active is really important to your health but it won't keep you thin - we need
to eat less to do that.
"Daily
energy expenditure might be an evolved trait that has been shaped by evolution
and is common among all people and not some simple reflection of our diverse
lifestyles."
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