by Selin Ilgaz
Why do we have meals instead of simply eating every time we feel hungry? Why are mealtimes structured and was this always the case?
For anthropologists human feeding behaviour comes from interplay between many environmental factors [1]. More specifically, foraging effort is obtained from an interaction between foraging opportunities (i.e. available resources and efficacy of foraging), limiting factors (i.e. population density, energy budget and allocation) and evolutionary factors (i.e. survivorship, reproduction and growth). Every living species including primates and humans have been through periods of famine and energy income shortages; therefore according to the point of view of anthropologists and behavioural ecologists, humans are equipped with genes that drive them to be careful with resources [1-2]. Thus, eating behaviours become opportunistic and in order to be favoured by natural selection, one has to be able to effectively store calories in times of abundant food availability [3]. Nowadays, technology and our environment provide us with plentiful opportunities forfood, without any food shortages, leading to an inevitable increase of calorie storage and therefore subsequently an increase of obesity. Modern neurobiological theories on feeding are based on a principle of homeostasis – our bodies are able to adjust to changes in conditions, such as high availability/intake of food, leading to a direct and indirect regulation of meal sizes [4]. However, this theory is not able to account for the reality that there is in fact an important increase of meal size and obesity and therefore today, it is considered that it may be more likely that our reward systems are over-activated by highly tasty and palatable food, leading to an alteration of the homeostatic balance [4].
If we look at the evolution of feeding behaviour, starting with our ancestors the non-human primates, we can clearly see that they differ from humans in their eating patterns. Like humans, they forage in groups, use tools, share their food but unlike humans, they do not gather and accumulate food. Instead, they have an opportunistic approach: the instant they find some food, they eat it [5]. Furthermore, it has been found that the times during which they do not eat in the presence of food is highly dependanton the environment like the palatability of the available food, the presence of social threat or the difficulty accessing it, therefore suggesting that the eating behaviour of non-human primates is not entirely controlled by internal biological mechanisms [6]. Moving to humans, when feeding behaviours of hunter-gatherers are observed, two of their defining features are crucial: an under-production of food and an absence of material accumulation [4]. Indeed, there has been no evidence of food storage until the latest human primate species, Homo sapiens. And even among Homo sapiens, food storage is highly dependanton external conditions. For instance, hunter-gatherers who depend on animal resources will find ways to preserve the meat collected during summer for harsh winter days. On the other hand, people living in equatorial regions – where the seasons are much less variable, will have poorly developed storage strategies compared to populations living in extreme conditions [4]. Despite storage differences inside various hunter-gatherer populations, humans are still the central foragers among all other species [7]. They all have a hub where they store the benefits obtained from hunting and gathering and it has been hypothesized that since there is a central location where food is stored, there have to be rules as to how the food is distributed, when, how much and by whom to whom. The procedure of a controlled distribution would have inevitably led to a structurization of meals and to dietary restraint [8].
To recapitulate, hunter-gatherers have a great capacity for adaptation to external conditions and have a great variability in their food habits among different hunter-gatherer populations. As they have experienced periodic food shortages and famines, calorie storage during times of surplus became crucial. Finally, in contrast to what is usually thought, hunter-gatherers don’t spend extreme amounts of energy, and usually forage only for 3-4h a day. They manage their calorie expenditure by foraging in large areas when food is abundant and save their energy by foraging in proximate areas when food is sparse. These characteristics of hunter-gatherers lead researchers to hypothesize that, meals and meal patterns may not be physiologically programmed but instead are solutions to food sharing issues and have a socialization function.[4].
The biggest issue that patterns of food consumption are facing now is meal size. People tend to finish whatever portion they are served,and in the USA meal sizes doubled in the last 20 years. It costs just a little more to serve bigger portions in restaurants, thus competition drives owners to escalate with their served portion sizes. Even though people are free to eat the amount they want out of their portions, it looks like there is an opportunistic behaviour at work, our “biological program” coming out telling us to eat it all when we can. Furthermore, food intake is highly influenced by plate size and social presence, showing that indeed meal size is not under physiological control but largely dependant on the environment.
Interestingly, it has recently been suggested that without any social restraints and norms on food patterns, snacking would be our natural form of eating. For Fischler, there is a breakdown of social rules of food – an anomie of eating; resulting with an increase in snacking and portion size and this loss of norm is what is leading to obesity [9]. The suggestion that snacking is our natural way of feeding is backed up by rodent studies.
The genetic, biological and behavioural characteristics of rodents closely resemble those of humans, and many symptoms of human conditions can be replicated in mice and rats, therefore they have been extensively studied in laboratories. It has been long thought that rodents have an internal regulator of meal intake, but Collier et al. challenged this theory by showing that the number of meals consumed by rats was actually influenced by the cost to reach the food and not by the number. Similarly, meal size was changing according to the number of meals taken and not by any biological factor [10]. For instance rats took only two meals a day when confronted to a high access cost situation while in easy access cases they were taking up to 10 meals a day, characterising them as “snackers”. We are biologically programmed to immediately attend to the smell or sight of food with an urgent response of whether or not to eat it. The food industry relies on that mechanism to grasp our attention and make us buy their products
References:
[1] Jenike MR. Nutritional ecology: diet, physical activity and body size. In: Panter-Brick C, Layton RH, Rowley-Conwy P, editors. Hunter-gatherers: an interdisciplinary perspective. Cambridge: University of Cambridge Press; 2001. p. 205–38.
[2] Pennington R. Hunter-gatherer demography. In: Panter-Brick C, Layton RH, Rowley-Conwy P, editors. Hunter-gatherers: an interdisciplinary perspective. Cambridge: University of Cambridge Press; 2001. p. 170–204.
[3] Gaulin SJC, Konner M. On the natural diet of primates, including humans. In: Wurtman RJ, Wurtman JJ, editors. Nutrition and the brain, vol. 1. New York: Raven Press; 1977
[4] Rowland NE. Order and disorder: temporal organization of eating. Behav Brain Res. 2012;231:272–278.
[5] Hohmann G. The diets of non-human primates: frugivory, food processing, and food sharing. In: Hublin J-J, Richards MP, editors. The evolution of hominin diets: integrating approaches to the study of palaeolithic subsistence. Springer; 2009. p. 1–14.
[6] Altmann SA. Foraging for survival. Chicago IL: University of Chicago Press; 1998
[7] Winterhalder B. The behavioural ecology of hunter-gatherers. In: Panter-Brick C, Layton RH, Rowley-Conwy P, editors. Hunter-gatherers: an interdisciplinary perspective. Cambridge: University of Cambridge Press; 2001. p. 12–38.
[8] Power ML, Schulkin J. The evolution of obesity. Johns Hopkins University Press; 2009.
[9] Fischler C, Masson E. Manger: Francais, Europeens et Americaains face a l’alimentation. Paris: Odile Jacob; 2008.
[10] Collier G, Hirsch E, Hamlin P. The ecological determinants of reinforcement in the rat. Physiol Behav 1972;9:705–16.
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