Epidemiological Data
Another argument against carbohydrate restriction is based on epidemiological evidence, and the Pima Indians are frequently cited. The Arizona Pima Indians have received the attention of the medical community because of their prodigious rates of obesity, which is nearly 70% among the adult population. Along with the reputation of being one of the most obese people known, the Arizona Pima has a rate of diabetes 8 times the national average with nearly 50% of the adult population over 35 afflicted with this condition.
In spite of innumerable studies, examining the Pima from every imaginable vantage point, there has been no defining discovery explaining the Pima's plight. One hypothesis favored by Eric Ravussn, Ph. D, is that after generations of living in the desert, the only Pima who survived famine and drought were those highly adept at storing fat in times of plenty. These "thrifty" genes which once ensured the Pima's' survival are now at the root of his demise.
Although it is not known for certain what metabolic processes these "thrifty" genes control, insulin resistance and glucose homeostasis are thought to be at the heart of the matter. Since preagricultural, man's diet was primarily derived from animal sources (protein/fat), an insulin resistant genotype would have minimized glucose utilization and thus, proven to be of an evolutionary advantage.
As primitive peoples have become acculturated and have assumed a modern diet, the constant supply of highly refined, high glycemic index carbohydrates has resulted in postprandial hyperinsulinemia and the subsequent diseases associated with this condition i.e. obesity, diabetes, cardiovascular disease, etc.
The Arizona Pima's diet prior to acculturation was essentially that of a hunter-gather with some subsistence farming: (chollacatus buds, honey mesquite, poverty weed, prickly pears, mule deer, white-winged dove, black-tailed jackrabbit, squawfish, and they raised wheat, squash and beans). However, by the end of the second World War, the Pima had almost entirely left their traditional lifestyle and adopted the typical American diet.
There are many problems with the typical American diet, and to blame the Pima's situation on just one element of that diet would be disingenuous. However, given the current scientific and anthropological studies, one could suggest that the high availability of sugar and highly refined, high glycemic carbohydrates (i.e. neocarbs), are at the core of the Pima's health crisis. It could also be extrapolated that, while the Pima's "thrifty" genes may work at a more accelerated pace, it is the same set of genes interacting with the same diet and producing the same results in the average American.
In 1991, the Pima's story became even more interesting. Peter Bennett FRCP, the lead epidemiologist studying the Arizona Pima, discovered in Sierra Madre, Mexico, the remnants of a tribe that once comprised the Southern half of the Pima Nation. However, unlike their Northern brothers, the Mexican Pima remained, in general, unacculterated and living a traditional lifestyle.
Also, unlike their northern counterparts, the Mexican Pimas were not obese, nor did they share in the Arizona Pima's high rate of diabetes and degenerative diseases. This dichotomy has been termed the "Pima Paradox." Since the Mexican Pima consume a diet comprised mostly of beans, potatoes, corn tortillas and the occasional animal product, (i.e. chicken) , this has often been used as the epidemiological case study for the benefit of high carbohydrate diets in obesity management.
However, two issues confound this example. First, on average, the Mexican Pima's have 23 to 26 hours/week of occupational physical activity versus the Arizona Pima's 5 hours or less. Certainly, such high levels of activity could mitigate the hyperinsulinemic effects of the Mexican Pima's diet.
The second issue is the "Enigma" within the "Paradox". Although the Mexican Pima does not have the health issues of the Arizona Pima, they still have a prevalence rate of diabetes at 6.4% (approximately 1.5x greater that the non Pima Mexicans), and a 13% incidence of obesity among the adult population.
While these numbers are impressive compared to the US population, and stellar compared to the Pima population, the question remains why should an essentially unacculturated population performing on average 23-26 hours of physical labor per week have any incidence of diabetes or obesity.
When modern day hunter-gatherers were studied by anthropologists, incidence of these conditions were non existent, even among the eldest members of tribe. The "evolutionary diet" model would thus suggest, in spite of their improved health over the Arizona Pimas, the Mexican Pimas are still consuming a less than optimal diet.
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