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samedi 28 juillet 2012

Energy expenditure: an explaining key of obesity?

Two examples of our trend to sprend less calories in the daily life:
Cold-induced thermogenesis
 Cold-induced thermogenesis is the production of heat in response to environmental temperatures
 below thermoneutrality. Cold-induced thermogenesis can be divided into two types: shivering
 thermogenesis and non-shivering thermogenesis. The thermoneutral zone (or the critical temperature)
 is the environmental temperature at which oxygen consumption and metabolic rate are lowest (IoM,
 2005). The relative contribution of cold-induced thermogenesis to TEE has decreased in recent
 decades due to the increase in time spent in enclosed and heated environments.
Thermic effect of food (TEF)
 Eating requires energy for the digestion, absorption, transport, interconversion, and deposition of
 nutrients. These metabolic processes increase REE, and their energy expenditure is known as the
 thermic effect of food (TEF). It should be noted that the muscular work required for eating is not part
 of TEF.

But it seems too simple...
Some are challenging our preconception that we spend less calories than hunter gatherers...

Pontzer H, Raichlen DA, Wood BM, Mabulla AZP, Racette SB, Marlowe FW. Hunter-Gatherer Energetics and Human Obesity. PLoS ONE 2012;7(7):e40503.
Individual comparisons of TEE and FFM.
Energy expenditure for Hadza hunter-gatherers (red circles) was similar to that of Westerners (gray[19][26]). Bolivian women farmers (blue open circles [13][31]) had higher TEE than either Hadza or Western women. Trendlines are ordinary least squares regressions through Western men (solid line) and Western women (dashed line).
Population comparisons of TEE.
Energy expenditure among Hadza hunter-gatherers (red circles) was similar to populations in market economies; subsistence farming populations (Nigeria, Gambia, Bolivia; blue circles) had higher TEE than other groups. All non-Hadza data from[16] (Text S1). Each symbol is a single-sex population mean; male and female means are plotted separately for mixed-sex studies. Ordinary least squares regression lines are shown for all men (filled circles, solid line) and all women (open circles, dashed line). When controlling for body mass, men had higher TEE than women (F(162) = 86.75, p<0.001).

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