Several studies have shown that the increase in the number of fast food restaurants in recent decades has had a negative impact on the already scandalous obesity rate. According to the National Bureau of Economic Research, the number of fast food restaurants over the past thirty years has tripled, which equates to approximately three hundred thousand establishments in the United States alone. During this time, the number of children aged six to nineteen classified as obese increased from five percent to seventeen percent. The percentage of adults classified as obese has increased from half to two-thirds of the population. Although fast food restaurants may contribute to the rising obesity rate in the United States, people are ultimately responsible for their own health. According to Dr. Joan F. Tryzelaar, obesity is defined as a medical condition in which excess body fat has accumulated to the point that it can have a negative effect on a person's health, leading to a reduction in life expectancy and an increase in heart problems. Obesity can be classified according to a person's body mass index or BMI. A BMI of twenty-five to twenty-nine is considered overweight, while a BMI of thirty or more is considered obese. The severity of a person's obesity can be further assessed in terms of fat distribution via hip/wait ratio and total cardiovascular risk factors. There are a number of reasons why a person becomes obese. Consuming too many calories is one of the most common causes of obesity. Since 2044, women have consumed an average of 1,877 calories per day, compared to 1,542 calories in 1971. Men consume an average of two... middle of paper ......ttp://www.medicalnewstoday.com/info/obesity/>.Dillner, Luisa. "Dr. Dillner's Health Dilemmas: How Much Exercise Should I Do to Stay Healthy?" » The Guardian. Guardian News and Media, July 30, 2012. Web. April 9, 2014. .Lüsted, Marcia Amidon. Obesity and food policy. Edina, MN: ABDO Pub., 2008. PDF. “Obesity and sleep. » Obesity and sleep 2. National Sleep Foundation, nd Web. April 9, 2014. Prakash, Reshma. "Physical inactivity a major cause of disease and disability, WHO warns." WHO. Np, nd Web. April 6, 2014..Tryzelaar, Joan F., MD. "Obesity." Cardiac Health. Np, nd Web April 7.. 2014..