Why do people become obese? People become obese for several reasons, including:

1. Consuming too many calories.
   People are eating much more than they used to. This used to be the case just in developed nations - however, the trend has spread worldwide. Despite billions of dollars being spent on public awareness campaigns that attempt to encourage people to eat healthily, the majority of us continue to overeat. In 1980 14% of the adult population of the USA was obese; by 2000 the figure reached 31% (The Obesity Society).
   
   In the USA, the consumption of calories increased from 1,542 per day for women in 1971 to 1,877 per day in 2004. The figures for men were 2,450 in 1971 and 2,618 in 2004. Most people would expect this increase in calories to consist of fat - not so! Most of the increased food consumption has consisted of carbohydrates (sugars). Increased consumption of sweetened drinks has contributed significantly to the raised carbohydrate intake of most young American adults over the last three decades. The consumption of fast-foods has tripled over the same period.
   
   Various other factors also may have contributed to America's increased calorie and carbohydrate intake:
   
   
   • In 1984 the Reagan administration freed up advertising on sweets and fast foods for children - regulations had previously set limits.
   • Agricultural policies in most of the developed world have led to much cheaper foods.
   • The US Farm Bill meant that the source of processed foods came from subsidized wheat, corn and rice. Corn, wheat and rice became much cheaper than fruit and vegetables.


2. Leading a sedentary lifestyle.
   With the arrival of televisions, computers, video games, remote controls, washing machines, dish washers and other modern convenience devices, the majority of people are leading a much more sedentary lifestyle compared to their parents and grandparents. Some decades ago shopping consisted of walking down the road to the high street where one could find the grocers, bakers, banks, etc. As large out-of-town supermarkets and shopping malls started to appear, people moved from using their feet to driving their cars to get their provisions. In some countries, such as the USA, dependence on the car has become so strong that many people will drive even if their destination is only half-a-mile away.
   
   The less you move around the fewer calories you burn. However, this is not only a question of calories. Physical activity has an effect on how your hormones work, and hormones have an effect on how your body deals with food. Several studies have shown that physical activity has a beneficial effect on your insulin levels - keeping them stable. Unstable insulin levels are closely associated with weight gain.


3. Not sleeping enough.
   If you do not sleep enough your risk of becoming obese doubles, according to research carried out at Warwick Medical School at the University of Warwick. The risk applies to both adults and children. Professor Francesco Cappuccio and team reviewed evidence in over 28,000 children and 15,000 adults. Their evidence clearly showed that sleep deprivation significantly increased obesity risk in both groups.
   
   Professor Cappuccio said, "The 'epidemic' of obesity is paralleled by a 'silent epidemic' of reduced sleep duration with short sleep duration linked to increased risk of obesity both in adults and in children. These trends are detectable in adults as well as in children as young as 5 years."
   Professor Cappuccio explains that sleep deprivation may lead to obesity through increased appetite as a result of hormonal changes. If you do not sleep enough you produce Ghrelin, a hormone that stimulates appetite. Lack of sleep also results in your body producing less Leptin, a hormone that suppresses appetite.


4. Endocrine disruptors, such as some foods that interfere with lipid metabolism.
   A team from the University of Barcelona (UB) led by Dr Juan Carlos Laguna published a study in the journal Hepatology that provides clues to the molecular mechanism through which fructose (a type of sugar) in beverages may alter lipid energy metabolism and cause fatty liver and metabolic syndrome.
   
   Fructose is mainly metabolized in the liver, the target organ of the metabolic alterations caused by the consumption of this sugar. In this study, rats receiving fructose-containing beverages presented a pathology similar to metabolic syndrome, which in the short term causes lipid accumulation (hypertriglyceridemia) and fatty liver, and eventually leads to hypertension, resistance to insulin, diabetes and obesity.
   
   Poorly balanced diets and the lack of physical exercise are key factors in the increase of obesity and other metabolic diseases in modern societies. In epidemiological studies in humans, the effect of the intake of fructose-sweetened beverages also seems to be more intense in women.
   
   Although there appears to be a consensus on the negative effects of fructose-sweetened beverages there is still some debate over the effects of fructose versus high fructose corn syrup.
   


5. Lower rates of smoking (smoking suppresses appetite).
   According to the National Institutes of Health (NIH) "Not everyone gains weight when they stop smoking. Among people who do, the average weight gain is between 6 and 8 pounds. Roughly 10 percent of people who stop smoking gain a large amount of weight - 30 pounds or more."


6. Medications that make patients put on weight.
   According to an article in Annals of Pharmacotherapy, some medications cause weight gain. "Clinically significant weight gain is associated with some commonly prescribed medicines. There is wide inter-individual variation in response and variation of the degree of weight gain within drug classes. Where possible, alternative therapy should be selected, especially for individuals predisposed to overweight and obesity.