Who is responsible for obesity?
Reduced physical activity or increased energy intake?
The main cause of abnormal fat accumulation is the chronicly sustained energy imbalance where energy intake exceeds energy expenditure. However, whether the emergence of a positive energy balance is due to excessive consumption of high energy density foods or reduced physical activity associated with our sedentary lifestyle remains a controversial issue.
What we knew until recently
Until a few years ago, it was undoubtedly claimed that the problem of the escalating frequency of obesity worldwide is due not to increased energy intake, but rather to reduced energy expenditure and more specifically to the lack of physical activity.
A number of surveys conducted in the 1970-2000 period to collect information on the eating habits of the developed country's inhabitants indicate a lack of any increase in the amount of energy consumed. And more importantly, according to these surveys, the consumption of fat has declined significantly over this period. In this way, irrational nutrition, and in particular the feeding of foods with high energy density, rich in simple sugars and fats, as well as their importance in the etiology of obesity, remained in the shadow of a much more discussed factor - physical activity.
Widespread was the notion that modern people leading the so- a Western model of life, extremely "full" use all the comforts offered to them by the modern world, and so have noticeably reduced their motor activity. Unlike us, our ancestors had to make significant daily physical effort and therefore did not have overweight problems. At the same time, it was more than obvious to everyone that the obese people around us are moving significantly less and that their energy expenditure due to physical activity is very limited.
An experiment comparing motor activity among modern humans with wildlife living in their natural environment showed lower than expected energy expenditure in humans and reinforced the belief that physical activity is the cause of the observed boom in the prevalence of obesity.
What we know today
Contrary to the results obtained through surveys that participants had to fill in, government data reporting production and sales of food products showed a significant increase in consumption of fat and simple sugars and energy respectively in the last 40 years. Since collecting information on the dietary habits of the population is one of the most complex issues of epidemiology, the causes of such inconsistencies have been sought for years. It turns out that in order to make a better impression, people tend not to adequately reflect the amount of food received and even limit their energy intake while they are under surveillance.
On the other hand, we can only guess how physically active our ancestors were. It is clear that cultivation of crops is an activity requiring considerable physical effort, but this was far from being the only source of livelihood in the past. Unlike agriculture, hunting is not always associated with a particular energy consumption.
An exemplary example in this respect is the kangaroo hunt practiced by Australian Aborigines who have spent hours standing in one place in anticipation of the approaching animal. The development and refinement of laboratory research methods has turned over some of the facts previously considered irrefutable.
The "double labeled water" method allows absolutely accurate measurement of daily energy consumption without any interference with the subject's motor and eating habits. By using this method, it was found that while obese people are less physically active, they have the same energy expenditure as people with a normal body, because moving larger mass requires more energy.
It also turned out that significant emptiness was made in the emblematic experiment comparing the energy consumption of human beings and wild animals. For example, there is no correction for the effect of anthropometric characteristics, body temperature of the species studied, environmental temperature, and individual energy needs on energy consumption. Taking into account all these factors would lead to radically different results from the study.
Therefore, until recently it seemed that the question of whether reduced physical activity or rather increased energy intake lies in the root of the development of obesity will remain open. At the end of 2008, however, it turned out that for nearly 30 years, a group of Dutch and British scientists have worked on this issue, but kept their results secret.
Immediately after approving "double-tapped water" for human use in the 1980s, they have conducted energy-saving studies on nearly 400 people living in the Netherlands. The same study was repeated in 2005 to make a direct parallel between the energy-wastage generated by physical activity these days twenty years earlier. Contrary to the recent belief that our physical activity dramatically decreases over time, thus stimulating the development of obesity, the results of this study show that physical activity has even increased slightly over the past 20 years.
For the same period, the prevalence of obesity in the Netherlands has increased by 4-5%. It is well known that obesity occurs due to disturbed balance of energy intake and energy expenditure. Therefore, this experiment, using the gold standard to measure the energy consumption of "double labeled water," unambiguously shows that reduced physical activity and increased energy intake is responsible for abnormal fat deposition.
Considering that the cited study was conducted among the population of only one West European city, it will be necessary to confirm the results repeatedly among a significantly larger number of people. Only then can the findings made on the basis of this experiment be unanimously accepted and put an end to a discussion lasting almost half a century. Until that moment, anyone with little knowledge of physical activity and nutrition can make the necessary conclusions for themselves.
Which is the more logical answer
It is hard to say with certainty whether reduced physical activity or increased energy intake is responsible for the progressive obesity of the world's population. It is most likely a combination of these two factors, where the excess weight of excess calories is overweight.
The average energy needs of an average man and woman are respectively 2500 and 2000 kcal. If we pay a little more attention to food packaging, we will notice that a wafer contains 400 kcal, a 500 kcal chocolate, and a menu at a fast food restaurant - 2000 kcal. On the other hand, the energy consumption associated with one-hour practice of some of the most common types of physical activity is as follows: walking 204 kcal / hour; cycling 260 kcal / hour; tennis 475 kcal / hour; weight lifting 530 kcal / hour; running at a moderate pace of 735 kcal / hour.
This means that if we run 3 one-hour workouts with weights (530 kcal / hour) and run for 2 times 40 minutes (735 kcal / hour) within one week, we will provide an energy efficiency of about 2500 kcal. At the same time eating 2-3 wafers and one menu at the fast food restaurant for this period will give us about 3,200 additional kilocalories. The final result will be a positive energy balance of about 1200 kcal in just one week.
From the example above, it can be seen that excessive intake of energy from food can hardly be compensated for by physical exercise. That is why it is more logical that the main culprit for the accumulation of extra pounds is to feed food with high energy density. However, lowering physical activity and reducing the time spent on exercise and sports add to the negative effect of feeding and thus further favor the development of obesity.
In conclusion - the results of a brand new research have turned over the recent perception that the main cause of the growing number of obese people is reduced physical activity, and have focused attention on gradually increasing energy per capita energy.
Most likely, however, it is a combination of these two factors. That's why if you want to reduce the likelihood of obesity and make yourself healthier, pay attention to your eating habits and include a few activities in your weekly plan.