A tale of two tribes: Genetically the same, but oh, so different

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It's a tale of two tribes, closely related, separated by time and distance . . . each with different story to tell and a radically different health profile to share with the rest of the world.

The Mexican Pima who inhabit in the mountainous region of the Sierra Madre, are Native farmers, living in traditional adobe rancherias, who cultivate corn, beans and potatoes, raise a few chickens and put in about 24 hours a week in hard physical labor on their land.

They eat about 2,200 calories a day, are lean, fit and healthy and have a normal rate of diabetes.

Their cousins to the north, the Pima Indians of the Gila River live in a dust blown reservation in central Arizona, and have lost touch with their traditional ways. The Gila River, which used to support rich fields of beans, grains and squash, has been all dried up, drained by the urban growth of nearby Phoenix.

The Gila River Pima, who eat about the same amount of calories per day as their genetically identical Mexican relatives, but average only about two hours a week in hard or culturally relevant labor, have now become famous for being fatter than any other group of people in the world (except for the Nauru Islanders of the West Pacific) as well as having the highest rate of diabetes in medical history; an astonishing 50 per cent of the population, eight times higher than the national average.

The ancestors of the two Pima tribes were some of the first people to set foot in the Americas, some 30,000 to 40,000 years ago.

And in a fascinating "reverse migration theory" modern archaeology suggests that the Pima in Arizona are descended from a prehistoric people down in Mexico called the Hohokam - "those who have gone" - master weavers and farmers who traveled north to where the Gila and Salt River meet, and made the desert bloom with a sophisticated system of irrigation and crop rotation.

Their descendants, the Gila River Pima, were able to maintain much of their traditional way of life until the early 19th century, when their water supply was diverted by American farmers settling upstream.

The complete disruption of an ancient way of life led to poverty and malnutrition, according to diabetes researcher, Dr. Eric Ravussin, forcing them to rely on government handouts of white sugar, flour and lard.

More leisure and a sedentary lifestyle, combined with a diet that had changed from a healthy traditional of high fibre and low fat to one that was very high in fat, led to profound physical changes in the Pimas, including obesity and a dangerously high incidence of diabetes.

These startling statistics were discovered 35 years ago when some researchers came to the reserve to do a routine comparative study on rheumatoid arthritis among Aboriginals, including the Blackfoot of Montana and the Arizona Pima. They soon realized that they had stumbled upon something much more significant, the possibility of not only studying the phenomenon of rampant diabetes in a closed population over a long period of time, but also the hope and expectation that such a study would lead to better ways of dealing with the disease.

One of the theories that emerged, favored by Dr. Ravussin, was what is now called "the thrifty gene theory", one that gave an advantage to Aboriginal people living on a traditional diet who also experienced seasonal cycles of feast and famine. This "thrifty gene" would make Aboriginal people, living in the desert, highly adept at storing fat in times of plenty, to tide them over times of famine and drought.

The big problem, in the case of the Gila River Pimas, is that such a gene would backfire and become a liability, given a post-contact sedentary lifestyle and high fat/low fibre diet.

The uniqueness and clinical value of more than 30 years of cutting-edge research into the genetic mysteries and environmental factors causing this diabetic plague lies in the fact that it is backed up by a genetically identical control group, the Pimas from the Sierra Madre in Meico who suffer little or no problems with the dreaded disease.

The studies have helped to crack open some of the mysteries of how diabetes works, how it is affected by obesity, and how it affects pregnant women and their yet-to-be born offspring.

Gluclose tolerance tests that help to keep blood sugar levels as normal as possible during pregnancies have now become routine all over North America because of what researchers and doctors have learned from the Pima Indian volunteers.

With a stable population of 11,000 on the reservation, researchers have also been able to follow the heredity factors through several generations. The collaboration between the National Institute of Health and the Gila River Pimas has been called one of "the most fruitful relationships in modern medical science" . . . one that will help people all over the world to control or avoid diabetes, have healthier eyes, hearts and kidneys, deal with the problems of obesity and try to understand all the ways that an unhealthy lifestyle can undermine our quality of life.