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 In
"The Desert's Perfect
Foods," Alan met members of the Tohono O'odham tribe
of Arizona. Though the Tohono O'odham, and their nearby relatives
the Pima, eat and exercise about the same amount as other
Americans, the tribe's obesity rate is more than twice that
among Caucasian Americans. Why? It is a question scientists
have been trying to answer since 1965. Dr. Eric Ravussin,
who has worked with the Pima for more than 15 years, weighs
in on the Pima paradox.
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Metabolic
Measures
Born
and raised in Luzon, Switzerland, Eric Ravussin always wanted
to be a scientist. After graduating from the University of
Luzon, Ravussin began work on his Ph. D, in human physiology,
perhaps inspired by the University's metabolic chamber - an
enclosed room that measures metabolic activity. As a post-doctorate
at the University of Vermont in Burlington, Ravussin worked
on a well-known feeding study of prisoners. After two years,
he returned to Switzerland.
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| Eric
Ravussin studies the genetic components of weight gain |
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In
1984, he returned to the states to set up a metabolic chamber
for the National Institutes of Health in Phoenix, AZ- not
far from the Pima reservation. The chamber would be used to
compare the metabolic rates of different ethnic groups, including
the Pima. Ravussin had planned to stay for just two years.
"But I guess I stayed for 16," he laughs from his office at
the Pennington Biomedical Research Center in Baton Rouge,
Louisiana.
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In the Pima, their survival mechanisms evolved to store
fat extremely efficiently.
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During
those 16 years, Ravussin's work with the Pima has illuminated
the genetic components of obesity. Ravussin estimates some
200 genes work together to control eating behavior and weight
regulation, though probably only 5 to 15 play the most important
roles. Why such a complex arrangement for something so crucial
as feeding?
"Any
important behavior needs alternate pathways," says Ravussin.
"When
it comes to survival mechanisms, you need redundant systems."
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| The
Arizona Pima showed no unusual rates of obesity pre-WWII
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In
the Pima, Ravussin's research indicates, their survival mechanisms
evolved to store fat extremely efficiently, a genetic make-up
that would have served the tribe well in the harsh desert
climes of the southwest. Today, however, this so-called "thrifty
gene" means roughly 70% of the Arizona Pima are obese.
"There's
no question these people suffer from a genetic disease," says
Ravussin. "It's not sloth and gluttony."
Type
II diabetes, strongly associated with obesity, is also epidemic
in the tribe, striking younger and younger children- something
almost unheard of in the general population.
"The
Pima have a genetic liability. But it's only a liability in
our environment," says Ravussin. "It was an asset to survival
in mankind's history."
Though
Ravussin's research has not yet isolated the genes and metabolic
pathways responsible for the Pima's obesity epidemic, he is
optimistic the work will one day help all overweight people.
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A Pima woman sits in a metabolic chamber |
"We've
known about the Pima's problem for 30 years, but nothing earthshaking
has been done," he says. "But I still hope, when we know the
exact genes, we will be able to correct the problem."
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