Obesity rates have increased dramatically in the last three decades, with the United States of America leading the way. The cause of this obesity is not known, but it is often assumed without question, that obesity results from a combination of an increased food intake and a reduction is physical activity. This imbalance is suggested to result in the accumulation of energy that is stored as body fat. Proponents of such a belief therefore see obese individuals as either lazy or greedy, and the solution offered to them is to limit energy intake through forced energy restriction, or to increase physical activity to remove excess body fat. In fact, evidence contradicts this viewpoint and shows that obesity is a metabolic disease characterised by insulin resistance in the liver and skeletal muscles. This results in an inability to correctly compartmentalise and utilise energy, with the result that triglycerides accumulate in abdominal and subcutaneous adipose tissue.
Despite evidence to the contrary, proponents of the ‘eat-too-much do-too-little’ hypothesis of obesity claim that increasingly sedentary lives are to blame for the epidemic of weight gain in Western countries. Often television and video games are blamed for this increasingly sedentary behaviour. However, evidence does not support this contention. For example, a study published in the International Journal of Obesity in 20081 investigated the energy expenditure from physical activity in countries from both Europe and North America, extending back in time to the 1980’s. The results showed that in Europe, in contrast to the claims, the physical activity expenditure had actually increased since the 1980’s. Likewise, physical activity also increased since the 1980’s in North America. The researchers also reported that the daily energy expenditure did not differ between subjects in Europe or North America with subjects in third world countries.
Therefore evidence does not support the contention that physical activity levels have decreased over time, and so this cannot be responsible for the increase in obesity rates. Extending the same logic shows that if decreasing physical activity levels are not to blame for obesity, then increasing physical activity would not be an effective strategy to treat obesity, as laziness is not the cause of the disease. The fact that daily energy expenditure is similar between Western nations where obesity rates are high, and third world countries where obesity rates are low, further supports the contention that physical activity is not to blame. The authors of this paper also calculated the daily energy expenditure of a 78 kg wild mammal living at 20°C to be 2190 kcal per day, which was lower than the 2428 to 3000 kcal required by a 70.5 to 78.6 kg human subject living in a Western nation. Therefore lack physical activity is not the cause of the obesity epidemic seen in Western Nations.
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