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Evaluate the relative contributions of changes in diet and in physical activity to the rise in the prevalence of obesity over recent decades.
How we can live in a world in which there are so many individuals suffering from malnutrition at the same time there are approximately 400 million adults who are obese? (www.who.int) Comparable statistics between these two extremes epitomise some of the global problems that we are faced with today such as health inequalities, social injustice and issues of Human Rights. As individuals we should all have the right to health, so how have we got to the point where many are exploiting these rights and have direct involvement in abusing their bodies? Through wider environmental changes in diet composition, food consumption, and the reduction of physical activity, a disproportionate imbalance of energy intake and energy expenditure is created which can result in the accumulation of excess body fat. Obesity is a contemporary concept that represents the single largest cause of morbidity and mortality throughout the western world (Cordain et al. 2005). It has rapidly proliferated in recent decades, which has lead to it often being seen as consequence of modern society. This is reinforced by evolutionary approaches that show the problem was almost non existent in our ancestral hunter-gatherer societies, suggesting that an evolutionary discordance exists between our human genome and these modern changes. Social and political factors also play a part and have huge influences on lifestyle choices and people's attitudes towards their bodies.
On a global level we can see that it is no longer just the affluent west that are seeing rises in obesity trends but this health problem seems to be spreading further afield to the developing world (Pollard, 2008). Globalisation is increasingly homogenising diets as local foods are now being crushed by a dominating, global food market. As a relatively new concept, obesity still has a window of opportunity for intervention and prevention. By re-educating society and providing them with opportunities for change, this problem can be tackled.
Humans as Hunter-Gatherers
Until 10,000 years ago, humans lived in small social groups with a subsistence strategy known as hunting and gathering (Trevathan et al. 2008). Hunter-gatherers are characterised as being nomadic, physically active and often had to survive in unpredictable environments which produced specific biological and behavioural adaptations. During times of abundance, energy intake was high, causing the body to store the excess in the adipose tissues ready for times of scarcity. It is this adaptation that can be seen as the downfall of the modern day Homo sapiens as the body is not adapted to food abundance. Eaton & Eaton (1999)show that the Palaeolithic diet was distinguished by a high reliance on wild plant and animal sources, a high intake of complex carbohydrates, high fibre intakes and low levels of saturated fats (Eaton, & Konner, 1984). Combine this with high levels of physical activity and it is easy to see why obesity was rare in these types of societies.
One main turning point in changes to diet was the Neolithic Revolution which involved a transition to agricultural subsistence, which meant that nutrient characteristics changed, lifestyles became more sedentary and populations increased. Leaving the ancestral lifestyle behind the rise to modernity brought food abundance, novel foods being introduced and a reliance on food processing procedures. This produced energy dense, highly palatable foods based on convenience and mass production that were alien to the human genome (Gard & Wright, 2005).The west is no longer at threat from scarcity but instead faces threats from the other end of the scale through supersizing trends. Some characteristics of contemporary diets are; high cholesterol, low fibre, high refined sugars and salt, refined carbohydrates and high saturated fat. Highly refined and processed carbohydrates and sugars replace that of natural complex macronutrients as seen in the hunter-gather diet (Trevathan, 2008). These refined foods are often void of any essential vitamins or minerals and also produce changes to the glycemic index, consequences of which affect insulin secretion therefore promoting the uptake of glucose for storage (Pollard, 2008). Fibre slows down the digestion process which results in lower insulin and glucose responses. In contemporary diets (where fibre intake is low) the effects are reversed which results in an increased rate in which glucose is absorbed into the blood often leading to diabetes and excess storage as fat. Stearns (1999) claims that modern Americans' fibre intake is approximately 1/5 of that of the traditional hunter-gatherer.
With an over reliance on fast food joints and ready meals, families are constantly being encouraged to live a convenience based lifestyle. Family meals around the table are a rare feature of contemporary society (Kaur et al. 2003) with meals now being consumed on the go, in the car or even at ones desk. The consequences of which are highly disastrous for the body as fast food oozes saturated fats, salt and an excessive amount of calories. Pollard (2008) suggests that it is not simply energy intake that has dramatically increased but it is this energy imbalance created by the lack of physical activity that is the driving force of obesity.
Physical activity is a crucial component in the energy balance equation (Pollard, 2008). Lehtonen & Viikari (1978) use an example of USA lumberjacks who consume approximately 4500-8000kcal/day but due to balanced expenditure their BMI is healthy a 25.5. High calorific intake is therefore cancelled out by increased physical activity. We must therefore look at changes that have occurred to physical activity levels in order to note its contribution to the obesity epidemic.
One consequence of the Industrial Revolution was changes in types of labour, more specifically, a decline in the need for physically intensive labour (Pollard, 2008). These days, jobs are more office based and exercise has now become a recreational activity rather than incorporated in labour. Physical activity seems to have been displaced to make way for other important aspects of the modern day life. Now we have Tesco delivery and many other modern day technologies that achieve in their aims to increase efficiency, but as a consequence, reduce our activity levels. Kaur et al. (2003) show the correlations between childhood obesity and the weekly hours of television watching. Results show that there is a consistent upward trend in the amount of hours a week spent by children watching television or playing on computer games which is displacing physical activity (Kaur et al, 2003). The traditional game of football has been replaced by Fifa Football games on the computer, so we can see modern day technologies replacing the real experience of going outside and playing sport. The virtual realm seems to be changing childhood experiences as we knew them. Through a lack of education on health there are often no real incentives to be of a normal weight and when you look at the USA with approximately 65% of all adult being overweight; individuals (especially children) must be confused as to what a normal weight is.
The Developing World
In the developing world, obesity can be seen as an effect of westernisation. As countries prosper in the benefits of industrialisation, they also become victims of its consequences. The best example of this can be seen in Nauru (South Pacific); a nation that is classified by WHO as having the highest prevalence of obesity and type two diabetes in the world (WHO, www.who.int). Explanations for the high obesity prevalence are based on biological approaches, behavioural and cultural approaches and also social and economic changes but we also cannot ignore those genetic factors that play a part in individual's responses to the environment (Hill & Melanson, 1999). Neel (1962) proposed the theory of the thrifty genotype in relation to Nauruan Islanders and other groups such as the Pima Indians. Neel (1962) believed that reproductive fitness would increase if an individual was able to release store energy during times of abundance and utilize energy during times of scarcity (Trevathan et al. 2008). He suggested that Nauruan individuals possessed a thrifty genotype that meant highly energetic foods could be stored efficiently. This adaptation became a problem when it was discovered that Nauru Island was made up of lots of high quality phosphate rock which was an economic gold mine for international mining companies. Nauru Island became one of the richest nations per capita and as westernisation took hold, most food began to be imported from Australia (Ringrose & Zimmet, 1979), calorie intakes almost doubled along with physical activity falling. Infrastructure and speed boats for fishing meant that the Nauruan people began to live a more sedentary lifestyle reflecting that of our own. Obesity soon became a huge problem with 34.4% of the population having type II diabetes and a life expectancy of males falling to 52.5 years old (Colaquiri et al. 2009).
Nauru is not unique in this rapid change to a westernised lifestyle affecting the health of its people. The same kind of patterns can be seen in the Pima Indians of Arizona who in comparison to their traditional Mexican Pima relatives, can be seen to be suffering from this exposure to the western world. Pima Indians living in America are approximately 25kg heavier than those living in Mexico (O'Rahilly, 2006). Obesity seems to be the price that society pays for progression.
Through looking at other Primates, there is also evidence to show that humans are more susceptible and vulnerable to obesity. Chimpanzees for example are believed to have 98% of the same genetic material as us and are seen to have relatively similar physical activity levels (Panter-Brick, 2003) yet there are very few cases of obesity within that species. This suggests that the triangulation of differences in diet, physical activity and environment may contribute to the prevalence of obesity in humans. The main question that arises in relation to obesity is; who is to blame? It comes down to individual choice over the foods we eat and the amount of exercise we partake in, but are we really such free, autonomous beings? Or are the constraints of our social environment influencing our bodies in ways that are out of our control?
By studying the social and political factors that contribute to the rise of obesity, we can try and weigh up this environmental influence. Anthropologist and physician Johan Galtung (1990) coined the term 'structural violence' to help explain global health inequalities. He claims that certain structures expose you to harmful risks and prevent you from reaching your full needs or potential (Galtung, 1990). For example he claims that if you are born in Sierra Leone, you are born into an environment with severe health problems so as an individual you have no control over the violence to the body and mind that you are faced with (Galtung, 1990). These health inequalities then cascade from one generation to the next. This concept can be seen to relate to obesity as by being born into certain social environments, individuals are more exposed to the risks that cause obesity. Through genetic inheritance, socialisation, social selection and access to certain resources, the chances of an individual becoming obese are increased under certain social and political contexts.
The distribution of obesity is not random (Brown & Konner, 1999) and throughout the literature we can see that social, biological and psychological factors play influencing roles on diet and physical activity levels. Society has gone through many changes over the last few decades which have affected all aspects of society. Lifestyles are now more sedentary in both labour and recreation, as well as diets being more processed and manufactured therefore replacing some of the goodness from natural nutrients with salts and fats. Evolutionary approaches suggest that we have advanced at such a speed that our metabolically thrifty body has not had time to adapt to modern day society. Food has gone from being a tool for survival to being one of the main causes of health problems throughout the western world. It is no longer simply a problem for the affluent west as modern day changes are spreading to a global level, taking with them some of the consequences of advancement; obesity being one of them. There is no one single causal pathway of obesity; causes are multi-factoral and complex, ranging from our genotype to our social environment, all playing their role in increasing our exposure to certain risks.
With increasing globalisation of foods, supersizing of meals and marketing campaigns capitalising on obesity, the future looks bleak. It is clear that both diet and physical activity are actively involved in the aetiology of obesity but the relative contribution of each is ever changing and needs to be a topic of further research.
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