The solution to the present obesity epidemic lies in recognizing its evolutionary origins. Obesity defined as excess body fat sufficient to impair mobility, could not have existed in hunter-gatherers of the genus Homo, because ineffective mobility would have impaired survival. The sole extant member of this genus, Homo sapiens (humans), lived as did its ancestors with a keen sense of hunger so as to maintain energy reserves required for mobility and survival in relative famine, and constrained by impairment of survival imposed by excessive weight. This changed when the “Black Death” ravaged southern Europe. During this period, to avoid contact with the substrate that was presumed to be contaminated, all social classes in Europe adopted the habit of wearing shoes. The associated discomfort of standing when using footwear caused avoidance behavior through extensive use of chairs for the first time in human history – a sedentary lifestyle and subsequent obesity for many, because unlike when humans were hunter-gatherers, technology now allowed less mobile humans to survive. Consideration of this perspective suggests that highly restrictive diets will typically fail to curb obesity, and instead, increasing daily weight-bearing time is essential. This will require avoidance of footwear whenever possible.
All members of genus Homo are descended from a common ancestor who must have lived in the Sub-Saharan savanna, and was likely a nomadic hunter-gatherer with a vertical posture.1 These early humans spent most of their wakeful hours weight-bearing – mainly standing but also walking and running.2 The development of a behavioral adaptation to prevent plantar skin ulceration resulting from prolonged standing was a precondition to this emergence. More specifically, all members of this genus rely upon a relatively small area of skin as a heavily weighted interface between their body and support surface. It is notable that plantar skin is durable when walking and running but loses protective value with prolonged standing without the addition of a behavioral protective mechanism, because glabrous skin (skin type of palms and plantar surface) though more resistant to mechanical forces than other skin types is susceptible to ischemic necrosis (death from lack of blood supply) arising from persistent loading.3-5 This plantar surface sensory mediated behavioral mechanism involving constant repositioning of plantar loads is likely ancient, considering that it was a precondition to the emergence of the upright stance characteristic of the genus.6-8
Obesity is defined here as excess body fat capable of impairing mobility. Sub-optimal mobility likely would have compromised survival of members of genus Homo from their emergence up until the time Homo sapiens developed adequate technology in animal husbandry and agronomy that would have allowed departure from nomadic life (c. 10,000 years ago).1,2 Natural selection optimized their nutritional balance via their sense of hunger. Onset of hunger commenced when easily available stored energy in muscle and liver began to be depleted. Sense of satiation was probably always weak as will be discussed later.
Even humans that gave up their nomadic life remained weight-bearing, since there is no evidence of widespread use of seating until modern times.9 This is explained by adaptation over time leading to inherent comfort of barefoot weight-bearing in humans. But it also suggests weight-bearing is inherently more comfortable than sitting because humans voluntarily remained weight-bearing for thousands of years after chair technology was known and living conditions allowed a more sedentary life.9
This changed suddenly when Renaissance Europeans became the first society in human history where all classes (particularly the less affluent masses) began wearing footwear. Pain from the feet of shod humans attempting to stand for long periods forced avoidance behavior via seating.9 The result was that Renaissance Europeans became the first sedentary population in history. This is the only available explanation of why chairs were rare prior to the Renaissance but common thereafter.9 The present worldwide use of footwear and sedentary lifestyle outside of Europe can be traced to European colonization and cultural imperialism.
The effect of this sedentary change on human energy requirements was massive. The MET (Metabolic Equivalent of Task) scale is used to simplify discussion of average energy consumed by a population of humans performing activities. One MET is defined as the oxygen consumption of 3.5 ml O2·kg−1·min−1 , which approximates the energy consumed when subjects are sitting quietly. Simply maintaining stable equilibrium in the upright position for short periods requires 1.8 METs, but performing minimal upper body work for prolonged periods upright requires considerable additional work to protect plantar skin from necrosis. This raises energy expenditure to about 3 METs – near the cost of walking slowly (3.5 METs).
From the emergence of genus Homo some 2,500,000 years ago, until the time when humans in Europe began using chairs at home and in the workplace, hunger had to become intense when energy intake was near 3450 kcal daily for a 70 kg human (the prototype in the discussion that follows). This is consistent with standing for all wakeful time (16 hours). Satiation probably was never fixed because of the variability of energy requirements with work, and the need for energy stored as body fat to be used when work intensity was great and/or food was scarce. Further, excessive body fat was constrained because it reduced mobility, making food gathering more difficult and less successful.
Contemporary obesity is the result of elimination of historical constraint on adiposity imposed by the need to be mobile, combined with an innate sense of hunger that drives humans to consume at least 3450 kcal daily and a poor sense of satiation. We will never return to a time when humans survived as hunter-gatherers. On the other hand, as intelligent animals, once informed, people would choose the healthier path if it does not disrupt their ability to work, travel and perform other required tasks of contemporary life. There are presently many practical ways that even the sedentary office worker can easily achieve the goal of 3450 kcal daily calorie consumption through exercise. For instance, it could be half met by working upright rather than in the seated position (remarkably, energy equivalent to competitive running for one hour). Remaining upright during transportation would be of further benefit. The goal could then be reached simply by adding a few intense exercise sessions weekly as is required for cardiovascular health. Obviously, most of this increase in energy utilization results from amplified weight-bearing time. Since much of any practical solution involves amplifying time standing, it will become necessary to wear shoes much less – e.g., being barefoot in the office and outside it when climatic conditions permit. The only obstacles to this are implicit and explicit social norms commencing with the European Renaissance that now force and encourage, respectively, footwear use.
People must be informed about the importance of eating only enough to satisfy hunger unless preparing for prolonged multi-day strenuous exertion as relying on the sense of satiation will surely lead to obesity. Once informed about the necessity of more exercise, most persons would be receptive so long as it is achieved without interfere with daily life imperatives. The alternative of hunger control through chemical means in presently unsafe. Even if improved pharmaceuticals become available, hunger suppression is a poor approach because unlike exercise, it does have secondary positive benefits on almost all organ systems.
Science is continually evolving though not linearly. Renaissance Europeans applied scientific principles considered advanced by the standards of their time by using footwear in a failed attempt to deal with contagious diseases that were devastating their society.10 This solution never resulted in disease control but was only proved ineffective by Koch near the beginning of the twentieth century. Data has suggested onl recently that footwear use is a major source of morbidity and mortality through causing our sedentary lifestyle and damaging our feet.6,11-14 This progression should not be used to support the argument that traditional practices must be sustained at the expense of scientific advances. Rather it argues for hesitation in incorporating new ideas that seem attractive in theory until they have been proven in practice. If this had been the standard of proof in the European Renaissance, footwear would have remained an ornament signifying social class as it had been for thousands of years prior to its general use in Renaissance Europe.
We have been slow in integrating scientific research in our daily lives via eschewing footwear, despite the recentness of developments in this area. This is in large part accounted for by resistance from groups that benefit from selling footwear and others that profit from the misery that shoes create. Nevertheless, ideas that improve health seem to get integrated into daily life rapidly in this age of electronic communication.
References:
1) Dunsworth, H. and Walker A. (2002). Early genus Homo. The Primate Fossil Record. (ed. W. Hartwig), 419-435. Cambridge: Cambridge University Press
2) Fleagle, J. (1999). Primate Adaptation and Evolution. Second Edition. New York: Academic Press
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9) Illustrated History of Furniture: From the Earliest to the Present Time. Frederick Litchfield. 1893
10) J Nohl, The Black Death: A chronicle of the Plague (London: Allen & Unwin, 1926)
11) Robbins SE, Waked E, Krouglicof N. Improving balance. J Am Geriatr Soc 1363-70 1998
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13) Robbins SE Gouw GJ McClaren J. Shoe sole thickness and hardness influence balance in older men. J Amer Geriatr Soc 1089-1994 1992
14) Robbins S. Waked E McClaren J. Proprioception and stability: Foot position awareness as a function of age and footwear. Age and Ageing 24:67-72 1995
