Being Human: Is obesity best understood as a social or biologically/evolutionarily-driven phenomenon?

As part of our first year Being Human module, students write an essay where they consider social and biological anthropological perspectives on a key topic in anthropology.  This week we are featuring an essay by Katie Goode.
Katie Goode
Katie’s bio: I am a first-year anthropology student from Berkshire. I came across anthropology unexpectedly when looking for a course to study and quickly realised it would become my passion. My initial curiosity was with the social aspects of anthropology. However, my fascination with biological matters has developed and made me appreciate the discipline as a whole.

The assessment of what is considered as ‘fatness’ and how it is measured has been greatly debated (Mueller, 1983). In 1972, the body mass index (BMI) was produced after being adapted from the Quetelet Index, which helped define individuals who were underweight or overweight (Nuttall, 2015). The Global status report on noncommunicable diseases 2014 from the World Health Organization indicates that there is obesity data from nearly every country in the world (WHO, 2014).  The report is based on BMI data, showing the extent to which BMI is globally used to represent fatness (WHO, 2014). However, there is extensive evidence that using BMI to understand fatness may be problematic (Nuttall, 2015). Using weight as a measure of fatness can lead to misrepresentation of people that are more muscular or have metabolic abnormalities, so body composition does not necessarily signify fatness (Blackburn and Jacobs, 2014). Consequently, research that is conducted using BMI data may be misconstrued. The use of BMI has compounded negative connotations around fatness. An alternative view would be from an evolutionary standpoint which suggests fatness was an adaptive quality.

In humans, fat to total body mass proportion ranges from approximately 10 per cent to over 35 per cent, making the human population one of the fattest mammals (Brown and Konner, 1987). Adipose tissue represents an energy store of fat content that is used to buffer against changes in dietary energy supply (Wells, 2010). In humans, although not all fat serves as an energy reserve, it has been argued that this is why fatness can be assumed to be ‘thrifty’ (Brown and Konner, 1987). During the evolution of hominins, a substantial number of metabolic demands were placed on expanding brain size and developing bipedalism (Trevathan, 2007). Due to there being such a high demand for nutrients to support these advancements, high-quality food was necessary for these traits to be developed (Trevathan, 2007).

In populations that struggled with a scarcity of food, a “thrifty genotype” that allowed the body to store excess amounts of calories as fat would have been selectively favoured, resulting in a higher body fat percentage (Trevathan, 2007). When going through periods of famine the body would be able to utilise these stores, making this trait advantageous. However, the idea that human adipose tissue evolved in response to famine is still debated as during famine periods death from starvation has not always been illustrated as the primary cause of death (Wells, 2010: 154). In the 19th century, during the Irish potato famine, only a minority of deaths could be directly related to starvation (Wells, 2010: 154). However, it could be that undernourished humans are more vulnerable to infections (Wells, 2010: 154). Nevertheless, having more adipose tissue could mean that the body can draw on energy reserves for long periods, which would help to survive famine (Wells, 2010: 154).

Females have been selected for having a slower release of peripheral body fat than men due to demands of pregnancy and lactation and it is likely that in some condition’s fatness would be an adaption to successful pregnancy (Brown and Konner, 1987). This helps to explain sexual dimorphism between human males and females as women evolutionarily benefited from having a larger amount of energy stores for pregnancy and lactation when food sources were low (Brown and Konner, 1987).

Due to ecological pressures from food scarcity as well as population growth, some societies began to move towards an economy based on agriculture (Brown and Konner, 1987). Moving from food foraging to agriculture was due to nutritional stresses in society (Brown and Konner, 1987). There is evidence that suggests sedentarism has been associated with an increased risk of obesity, which may have played a role during this modernisation of diets (Prentice and Jebb, 2004). Food sources have changed dramatically in many parts of the world as ancestral populations mostly ate wild plants and animals, whereas modernisation has led to diets being made up of grains, refined sugars, dairy and meat from domesticated animals (Trevathan, 2007). Western diets are now higher in fats, sodium and sugar and low in complex carbohydrates and fibre, compared to ancestral populations (Trevathan, 2007). The desire for these fatty, sweet foods would have been advantageous for hunter-gatherers, however, in today’s industrial societies this is problematic when there is such an abundance of fatty foods that are so obtainable (Trevathan, 2007). Humans do not regulate food quantities to intake less when the energy density of food is so high, which can cause an excessive amount of food intake (Prentice and Jebb, 2004). Due to nutritional needs evolving in circumstances so different from contemporary diets, it has left a mismatch between the diets many modern-day humans consume and their biology (Trevathan, 2007). Obesity is not an issue for all humans but some societies that have such affluence that there is enough access to food that even the poor can become obese (Brown and Konner, 1987).

Genes that have evolved in environments of scarcity cannot be expected to accommodate such rapid changes of high energy intake (Wells, 2007). Twin and adoption studies have suggested that up to half of inter-individual variation in total fatness and distribution is in fact due to genetics (Wells, 2007). Mutations in the genes that regulate leptin metabolism have been found in patients with severe obesity, suggesting that rare single-trait conditions could affect fatness (Wells, 2007). The rarity of these genes means that they cannot explain current obesity rates in Euro-American societies (Wells, 2007); however, multiple studies that have been carried out on measuring skinfolds and other parts of the body indicate that there is a strong genetic component to fatness (Mueller, 1983). One study of dizygous and monozygous twins showed that genetics play a strong role in fatness when using measurements of physically tangible fatness. However, later research with a reduced sample of adult twins determined that environmental factors also largely determine adult fatness, reflecting a possibly greater social component to adult fatness (Mueller, 1983). Fatness could be better understood as a result of genetic and environmental factors such as dietary composition – as there is also evidence suggesting high protein in early life may programme for obesity (Wells, 2007). An adoption study aiming to find out if cohabitation had effects on fatness looked into two groups of foster mothers (one overweight, the other normal weight) and used BMI to measure the fatness of the foster children (Mueller, 1983). The children who had overweight mothers had much higher BMI’s than the normal weight mothers, suggesting there may be a greater social component to fatness (Mueller, 1983).

Rebecca Popenoe’s research has focused closely on the people from Tuareg culture as well as from Moorish culture, where fattening is used to accelerate puberty and aid girls in marriageability (Popenoe, 2003: 39). Both cultures sexualise female fatness and celebrate skinfolds females get from this process (Popenoe, 2003: 39). For many women in these cultures, their life purpose is to fatten, and the fattening process is not just about the size of their body but how it educates them on their place in society (Popenoe, 2003: 41-42). Between these cultures and their Western counterparts, there are vast differences in how fatness is perceived. Even dolls in each culture reflect each societal standard of women’s plumpness, one being large and curvy and the other being the traditionally slim Barbie doll (Popenoe, 2003: 43). There are many examples of this ideal for plumpness in societies that have not been so westernised (Brown and Konner, 1987). Nevertheless, there has been no extensive research looking at body type standards cross-culturally (Brown and Konner, 1987).

When determining eating behaviour, the social environment is of great importance (Feunekes et al., 1998). The impact of social influences on eating behaviour is substantial whether an individual realises it or not, when in a social situation we may alter how much food we consume as well as what we consume (Feunekes et al., 1998). This also impacts food decisions when individuals are eating alone as social influences engrain habits and behaviours into decision making (Feunekes et al., 1998). When looking at resemblances in food intake in Fuenekes et al.’s study, food item intake frequency between husbands and wives (94% of items) and of mothers and children (87%) were the highest of the results (Feunekes et al., 1998). But when looking at snack foods and alcohol intake this was greatly associated with friends (Feunekes et al., 1998). This research illustrates that a person’s social group will greatly impact the diet that they consume. We can then infer that if an individual ate a high fat and sugar diet, this would greatly affect the diets of those around them. In modernised, western societies where high-fat foods are so cheap and readily available, it is likely that these social influences affect many people.

Robinson et al.’s (2013) research further supports the idea of social interactions affecting food intake. A group of participants were led to believe that a group before them had either eaten a large or small amount of food. When making the participants think that the normal intake was to eat a lot of food, the food intake increased and when the norm was to eat less food intake reduced. These results suggest that when led to believe others around an individual are eating large amounts of food, this may promote overconsumption, even when eating alone. It has been suggested that social factors such as overconsumption of food may contribute to weight gain and specific eating patterns within social networks (Robinson et al., 2013). Some evidence further suggests that the presence of peer effects contributes to weight gain in adolescents (Fortin and Yazbeck, 2015). As adolescents often compare themselves to their peers, they may change their eating behaviours to fit in with the social groups that they are in (Fortin and Yazbeck, 2015). Fortin and Yazbeck (2015) found that when increasing friends’ mean fast food consumption this led to adolescents in that social group also increasing their fast-food consumption. As adolescents begin to gain independence and have more freedom with what they eat, it is very easy for them to be able to change their diets to what individuals around them are eating (Fortin and Yazbeck, 2015). With this in mind, due to the lower price and easy availability of fast food increasing, this could generate an even further increase in the prevalence of fatness (Fortin and Yazbeck, 2015).

An important factor concerning the social debate on fatness is its association with social class in western contexts (Brown and Konner, 1987). During childhood, middle and upper-class girls are fatter than lower-class girls but when these children reach puberty the fatness in the groups switches (Brown and Konner, 1987). Lower class women are consistently bigger than middle and upper-class women in adulthood, suggesting a relationship between obesity and social class (Brown and Konner, 1987). Due to cheaper foods usually being fast food or other foods high in fat and sugars, unsurprisingly, lower-class individuals become fatter than those in the middle and upper-class later on in life. This suggests that in western social climates it is likely that the lower class will continue to be overweight unless a change occurs which allows healthier foods to be more readily available at a lower price.

For a trait such as fatness that has such strong social-environmental and genetic origins, it is not surprising that research remains inconclusive regarding the cause of obesity, but current and previous research does help to give a better understanding of fatness and its origins (Mueller, 1983). In the area of adult fatness, more research needs to be carried out to find more conclusive explanations on whether fatness is biologically or socially driven. To conclude, the phenomenon of obesity is predominantly biologically driven; however, social influences have great effects on people’s diets, meaning the fatness of societies will constantly alter.

 

References

Blackburn, H. and Jacobs Jr, D. (2014) Commentary: Origins and evolution of body mass index (BMI): continuing saga, International Journal of Epidemiology, 43(3), pp. 665-669. doi:10.1093/ije/dyu061

Brown, P, J. and Konner, M. (1987) An Anthropological Perspective on Obesity, Annals of the New York Academy of Sciences, 499, pp. 29-46. doi:10.1111/j.1749-6632.1987.tb36195.x

Feunekes, G, I, J., Graaf, C, D., Meyboom, S. and Staveren, W, A, V. (1998) Food Choice and Fat Intake of Adolescents and Adults: Associations of Intakes within Social Networks, Preventive Medicine, 27(5), pp. 645-656. doi:10.1006/pmed.1998.0341

Fortin, B. and Yazbeck, M. (2015) Peer effects, fast food consumption and adolescent weight gain, Journal of Health Economics, 42, pp. 125-138. doi:10.1016/j.jhealeco.2015.03.005

Mueller, W, H. (1983) The genetics of human fatness, American Journal of Physical Anthropology, 26(1), pp. 215-230. doi:10.1002/ajpa.1330260510

Nuttall, F, Q. (2015) Body Mass Index: Obesity, BMI, and Health: A Critical Review, Nutrition Today, 50(3), pp. 117-128. doi:10.1097/NT.0000000000000092

Popenoe, R. (2003) Feeding Desire: Fatness, Beauty and Sexuality among a Saharan People. Milton, UK: Taylor & Francis Group

Prentice, A. and Jebb, S. (2004) Energy Intake/Physical Activity Interactions in the Homeostasis of Body Weight Regulation, Nutrition Reviews, 62(2), pp. 98-104. doi:10.1111/j.1753-4887.2004.tb00095.x

Robinson, E., Benwell, H. and Higgs, S. (2013) Food intake norms increase and decrease snack food intake in a remote confederate study, Appetite, 65, pp. 20-24. doi:10.1016/j.appet.2013.01.010

Trevathan, W, R. (2007) Evolutionary Medicine, Annual Review of Anthropology, 36, pp. 139-154. doi:10.1146/annurev.anthro.36.081406.094321

Wells, J, C, K. (2007) The Evolution of Human Fatness and Susceptibility to Obesity: an ethological approach, Cambridge Philosophical Society: Biological Reviews, 81(2), pp. 183-205. doi:10.1017/S1464793105006974

Wells, J, C, K. (2010) The Evolutionary Biology of Human Body Fatness: Thrift and Control. Cambridge, UK: Cambridge University Press

World Health Organization (2014) Global Status report on noncommunicable diseases 2014. Available at: https://www.who.int/nmh/publications/ncd-status-report-2014/en/ (Accessed: 06 April 2021)

 

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