What are the Causes of Obesity?

Obesity is a multifactorial disease; in other words, it is a disease in which many causes play a role. Among these, overnutrition, malnutrition, and inadequate physical activity are considered to be the most important causes. In addition, genetic, environmental, neurological, sociocultural and psychological factors play a role as well. The increase rates of childhood obesity all over the world suggest that environmental factors are more prominent than genetic factors.

Dietary patterns in early years of life have been found to affect obesity in later ages. According to the World Health Organization study, obesity and chronic disease risk can be lowered in children exclusively breastfed for a period of 6 months, with continued breastfeeding for at least 2 years. To sum up the effective factors in obesity;

What are the Causes of Obesity?

1-Excessive Consumption of calories


The caloric intake of these days’ people is higher than that of the previous generations. The factor is not only the easy access to cheap high-calorie foods but also the fact that foods are becoming increasingly more processed foods with higher industrial sugar content. Moreover, this is not a problem suffered only by developed countries, but shows an increase all over the world.

Despite billions of dollars being spent on public awareness studies intended for encouraging people to eat healthily, the great majority of the society continues to eat excessively. The prevalence of obesity has doubled all over the world over the last 10 years. For example, the prevalence of obesity in the United States that was 14% in 1980 reached 31% by 2000.

According to studies, the consumption of calories in the USA that was 1,542 per day for women increased up to 1,877 per day by 2004. And in men, the figure increased from 2,450 to 2,618 in the same period. The most important cause of this increase in caloric intake is the boom of carbohydrate foods and sugar production experienced under compulsion of the industry. The most important factor responsible for the increased caloric intake—especially in young adolescents—is the consumption of sugary drinks and fast-foods. The consumption of fast-foods has tripled over the last three decades.

Other reasons that increase calorie consumption are the facts that the sugar lobbies have influence over food policies; the agricultural policies have paved the way for the consumption of more cheap and poor quality foods especially in developed countries; and foods such as genetically modified corn and corn syrup are cheaper than vegetables and fruit.

Contrary to popular belief, obesity does not appear instantly; instead, it appears as a result of excessive calories accumulating gradually over the years. For example, let’s consider a 40-year-old woman weighing 105 kg, who weighed 60 kg when she was 20 years old. This person gained about 2.5 kg each year. 1 kg fat corresponds to 3,500 calories. Accordingly, 2.5 kg fat corresponds to17,500 calories. Daily average caloric intake is equivalent to 1,800 calories. Yearly average caloric intake is 657,000 calories. So, she gained 2.5 kg each year just due to excessive caloric intake in an amount 2.6% higher than what we can burn a day, i.e. extra 48 calories per day. 48 calories correspond to almost half a slice of bread. This example shows the importance of developing wise nutrition tactics for the prevention of obesity. It also gives clues about the impossibility of treating obesity by only preventing that extra 50 calories. If it was possible, diet and exercise would work in all patients.

2-Sedentary Lifestyle: With the technological progress and the devices such as televisions, computers, video games, washing machines, dish washers and automobiles that became an inseparable part of our daily life, these days people adopted a much more sedentary lifestyle compared to their parents and predecessors. Just fifteen years ago, even shopping required walking a certain distance, but then the number of shopping malls and fast food restaurants that make home delivery has increased in all the cities. Even if it is not so, car addiction has progressed so much that people began to go by car to a buffet located a half kilometer away to buy bread.

As the amount of movement decreased, the amount of caloric intake got minimized. But the problem is not just about caloric intake. Physical activity affects even the functioning of your hormones and the processes needed when the foods you eat are processed. In many studies, the beneficial effects of physical activity on insulin levels have been proven. A study published in the January 2012 issue of the American Journal of Preventive Medicine showed that children who had a television in their bedroom were at a higher risk of being obese and overweight, compared to those who didn’t have a television in their room.

3-Inadequate Sleep: Studies have shown that inadequate sleep doubles the risk of obesity. This risk is for both children and adults. The epidemic of obesity in children and adults is paralleled by the silent epidemic of insomnia. Shortening of sleep durations and decrease in sleep quality lead to hormonal imbalance and increased appetite. When you do not sleep enough, your body secretes Ghrelin, a hormone that stimulates appetite. Inadequate sleep also leads to inadequate production of leptin, a hormone that suppresses appetite.

4-Foods affecting the endocrine system, which also interfere with the fat metabolism: A study conducted at the University of Barcelona showed that fructose (fruit sugar) intake affects lipid energy metabolism and consequently leads to fatty liver and metabolic syndrome. Fructose is basically metabolized in the liver. The liver is the target organ, where sugar consumption causes metabolic affects. The study showed that a condition similar to metabolic syndrome developed in rats fed with fructose-containing foods, which caused higher levels of blood lipids, fatty liver, and eventually led to hypertension, resistance to insulin, diabetes and obesity.

Imbalanced diet and the lack of physical exercise are the key factors responsible for the increase of obesity and other metabolic diseases in modern societies. The new epidemiological studies showed that the consumption of fructose-sweetened beverages have more severe effects on women in particular. Fructose is abundant especially in corn syrup, which is used in the production of almost all industrial beverages.

Researchers from Yale University compared the effects of fructose and glucose on the brain with MRI scans, and asserted that a high-fructose diet may be the underlying cause of the current obesity epidemic.

In an article published in JAMA (Journal of the American Medical Association), it was stated that the region in the brain that regulates appetite became active in people who consumed glucose, but remained inactive when they consumed fructose. If those regions become active, the hormones that produce the feeling of satiety, i.e. the stimulants telling you to stop eating, are released.

5-Certain Medications: According to an article published in Annals of Pharmacotherapy, some commonly prescribed medicines may cause weight gain. This effect of corticosteroid drugs and some antidepressants in particular are known. Since the effects of these drugs vary from person to person, their alternatives should be preferred (if possible) especially in overweight and obese individuals.

6-Perpetuation of Physical Obesity: Losing weight is known to become harder in parallel with the length of the period in which a person is overweight. This information suggests that obesity is a condition that reinforces itself and tries to become a permanent state. According to an article published in the Journal of Clinical Investigation, some findings obtained in animal experiments suggested that obesity is a condition reinforcing itself. These findings show the importance of intervening in childhood obesity as early as possible and ensuring children to be protected from this condition—that may affect whole of their lives—and to be treated as soon as possible.

This study also clarifies why adults have difficulty in losing weight successfully with diet and exercise alone, after reaching a certain degree of obesity. In addition to this study, research published in the journal Nature Communications in 2015 showed that losing weight gets harder in parallel with the increase in fat that we carry in our body. The more increase in fat, the more production of a protein that prevents the body from burning fat.

7-Obesity gene: According to an article written by a team of researchers from University College London, published in the July 2013 issue of the Journal of Clinical Investigation, a faulty gene called FTO seems to be the cause of overeating in one in every 6 people. People who carry the FTO gene variant tend to eat much more high-energy and fatty foods, and are generally obese. Such people also need a longer time to feel satiety.