It’s not about Western Lifestyle!

September 26th, 2012 by MorganDowney Leave a reply »

Herman Ponzer of the Department of Anthropology at Hunter College and colleagues have challenged one of the major assumptions in current thinking about obesity. The assumption is that Western lifestyle differs markedly from those of our hunter-gatherer ancestors and that these changes are responsible for our current obesity epidemic. To look at this Ponzer and colleagues studied daily energy expenditure of the Hadza foragers. The Hadza live in a savannah-woodland environment in Northern Tanzania. It is believed that the lifestyle of the Hadza are similar in critical ways to our Pleistocene ancestors. Hadza women gather plant foods; while the men engage in hunting. 95% of their calories come from wild foods including tubers, berries, game, baobab fruit and honey. The researchers expected that the Hazda would have lower body fat than Western populations and that, with their natural diet and lack of mechanization, they should expend more energy than individuals living in market economies with comparatively sedentary lifestyles and more energy dense diets.

Surprise! The authors state, “Contrary to expectations, measures of TEE (total energy expenditure) among Hadza adults was similar to those in the Western (U.S. and Europe) populations.” Because the Hadza are smaller than Westerners, their energy spent on their basal metabolic rate (BMR) was smaller than for Westerners. According to the researchers, “ Measurements of TEE among Hadza hunter-gatherers challenge the view that Western lifestyles result in abnormally low energy expenditure, and that decreased energy expenditure is a primary cause of obesity in developed countries. Despite higher PAL (physical activity level) and dependence on wild foods, Hazda TEE was similar to Westerners and others in market economies. Further, while Hadza differed from Western populations in body fat percentage, variation in adiposity both within and between populations was not correlated with PAL nor with TEE. The lack of correspondence between TEE, PAL, and adiposity in our Hazda and comparative samples is consistent with previous DLW (doubly labeled water) studies in Western populations. The similarity in TEE among Hadza hunter-gatherers and Westerners suggests that even dramatic differences in lifestyle may have a negligible effect on TEE, and is consistent with the view that differences in obesity prevalence between populations result primarily from differences in energy intake rather than energy expenditure…Data on hunter-gatherer TEE provide additional perspectives on Paleolithic humans and on the origins of farming. While the lifestyle of late Pleistocene hunter-gatherers was no doubt highly active as seen in foragers today, our results suggest that their daily energy requirements were likely no different than current  Western populations…TEE is remarkably similar across a broad, global sample of populations that span a range of economies, climates and lifestyles. Not only is TEE statistically indistinguishable between Western, foraging, and farming population levels. We hypothesize that TEE may be a relatively stable, constrained physiological trait for the human species, more a product of our common genetic inheritance than our diverse lifestyles.”. They cite another study pointing to the body’s complex physiological responses to dieting and weight loss support this view PubMed_Hunter Gatherer Energetics and Human Obesity

This is not the first study making this observation. Ramon A. Surazo-Arizu of Loyola University Medical School and colleagues studied the rise of obesity in three countries: Jamaica, Nigeria and the United States. They found that women in Nigeria and the US had higher weight gains than men but the reverse was true for Jamaicans. They write, “The steep trajectory of weight gain in Jamaica, relative to Nigeria and the US, is most likely attributable to the accelerating effects of the cultural and behavioral shifts which have come to bear on transitional societies.” The three countries span economic development from highly developed (U.S.) to middle-income (but stagnant in Jamaica’s case) to low-income (Nigeria). The average weight gain was .43 kg/year in Nigeria, 1.28 kg/year in Jamaica and .38 kg/year in the US. The researchers observed, “The prevalence of obesity was lowest in Nigeria, although during this time period participants in that rural community were gaining about as much weight as those followed in the U.S…Over the last 10-15 years societies as geographically and culturally distant as Barbados, Russia, Kuwait, and Japan have all experienced rapid increases in relative weight, affecting both children and adults. In the US the shift in the BMI trend slope occurred in the mid-1980’s and a 5-fold increase in the rate of change/year has been observed subsequently. Even Norway – with its historically low obesity rates and high participation in leisure time physical activity – experienced an abrupt up-turn around 1990. Clearly some “common source exposure” is shifting the population distribution of weight right-ward and virtually all segments of the societies that participated in the world economy are being affected. While it is assumed that lifestyle changes related to the growing consumer economy are the driving force it has been difficult to define and quantify the specific factors…Although Jamaica has undergone rapid cultural changes over the last 20 years, accompanied by a decrease in the rural population, it has experienced stagnating or negative economic growth. While accurate economic data are difficult to obtain, it is also unlikely that average Nigerians have seen any substantial increase in their material standard of living over the last 2 decades. Thus, the lifestyle changes required to fuel weight gain do not require general economic development, and instead may reflect the penetration of market-based consumption patterns into stagnating or declining economies. These observations suggest that it is the character of social development, not necessarily the level of economic activity per se that is driving the combined obesity-diabetes epidemic in many poor and middle-income countries.” PubMed: Rapid increases in obesity in Jamaica, compared to Nigeria, US

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