What Causes Obesity

A 2006 review identifies other possible contributors to the recent increase of obesity: (1) insufficient sleep, (2) endocrine disruptors (environmental pollutants that interfere with lipid metabolism), (3) decreased variability in ambient temperature, (4) increased use of medications that can cause weight gain (5) relative increases in ethnic and age groups that tend to be heavier, (6) pregnancy at a later age (which may cause susceptibility to obesity in children).

A sedentary lifestyle plays a significant role in obesity. Worldwide there has been a large shift towards less physically demanding work, and currently at least 60% of the world's population does not get sufficient exercise. This is primarily due to increasing use of motorized transportation and a greater prevalence of labor saving technology in the home.

World trends in active leisure time physical activity are controversial. The World Health Organization indicates that worldwide people are taking up less active recreational pursuits however a study from Finland found an increase but a study from the United States found leisure-time physical activity has not changed significantly.

Studies in children and adults have found an association between the number of hours of television watched and the prevalence of obesity. A 2008 meta analysis found that 63 of 73 studies (86%) showed an increased rate of childhood obesity with increased media exposure, and rates increasing proportionally to time spent watching television.

Diet Causes of Obesity: From the early 1970s to the late 1990s the average calories available per person per day (the amount of food bought) has increased in all parts of the world except Eastern Europe.

The United States still had the highest availability with 3654 calories per person in 1996. During this same time period Europeans had 3394 calories per person, in the developing areas of Asia there were 2648 calories per person, and in sub-Sahara Africa people had 2176 calories per person. US per capita daily availability increased further in 2002 to 3770.

The widespread availability of nutritional guidelines have done little to address the problems of overeating and poor dietary choices and may have actually contributed to the problem. In the period of 1971–2000, obesity rates in the United States increased from 14.5% to 30.9%. During the same time period, an increase occurred in the average amount of calories consumed.

For women, the average increase was 335 calories per day (1542 calories in 1971 and 1877 calories in 2004), while for men the average increase was 168 calories per day (2450 calories in 1971 and 2618 calories in 2004). Most of these extra calories came from an increase in carbohydrate consumption rather than an increase in fat consumption.

The primary sources of these extra carbohydrates are sweetened beverages, which now accounts for almost 25 percent of daily calories in young adults in America. Consumption of sweetened drinks is believed to be contributing to the rising rates of obesity.

As societies become increasingly reliant on energy-dense, large portion, fast-food meals, the association between fast food consumption and obesity becomes more concerning. In the United States consumption of fast food meals has tripled and calorie intake from fast food has quadrupled between 1977 and 1995.

Agricultural policy and techniques in the United States and Europe have led to lower food prices. In the United States, subsidization of corn, soy, wheat, and rice through the U.S. farm bill has made the main sources of processed food cheap compared to fruits and vegetables.

There is little evidence to support the commonly expressed view that some obese people eat little yet gain weight due to a slow metabolism. On average obese people have a greater energy expenditure than thin people. This is because it takes more energy to maintain an increased body mass. Obese people also under report how much food they consume compared to those of normal weight. Tests of human subjects carried out in a calorimeter support this conclusion.

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