Abstract
Physical inactivity is a major public health problem in developed countries, and the fourth leading mortality risk factor globally. Recently, it was suggested that the total energy expenditure of sedentary Western population is similar to the total energy expenditure of Hadza hunter-gatherers known for their traditional foraging lifestyle in the savannah-woodland environment.
However, this claim was based on the similarity of metabolic rates of walking and resting, and completely ignored the effects of different total energy expenditure normalized to the fat free body mass in individuals of different height and weight. The above claim stemmed from mixing the effects of tissues with low metabolic rate (bone) and those with high metabolic rate (muscle, liver, brain, etc.).
Thus, the total energy expenditure is not similar among the sedentary Westerners and the Hadza hunter-gatherers. While the total energy expenditure recorded for basic human activities is similar across a broad range of cultures and lifestyles when adjusted to the weight, the unadjusted values differ.
Thus, increase in body mass, and particularly the obesity, serves as compensatory total energy expenditure increasing mechanism resulting from the combination of low physical activity levels and high long-term total energy intake. Thus if two individuals at iso-energetic conditions match their energy demand with different substrates' contribution, it may be caused, e.g., by their reliance on a different contribution of fatty acids oxidation to cope with energy demand.
Differences in substrate partitioning need to be addressed when assessing the energy expenditure across multiple human populations.