Obesity is defined as having an amount of excess body fat resulting in a body mass index (BMI) of over 30 kg/m2. BMI is computed, using the metric system, from dividing a person's mass by the square of one's height [mass/(height2)] (to calculate your BMI click here). If a BMI is less than 18.5, a person is considered underweight. If a BMI is between 18.5 and 25, it is considered optimal weight. A BMI between 25 and 30 is considered overweight and a BMI above 30 is considered obese.
The most common cause of obesity is consuming excessive calories combined with insufficient physical activity-in other words, eating too much and lack of exercise. Additionally, genetic susceptibility is a factor, meaning that certain people's genes make them more likely to become obese. A small amount of cases are caused specifically by the endocrine system (glands and hormones), medications or mental illness; however, the vast majority of cases are due to unhealthy lifestyle.
Obesity adversely affects the general well-being of a person, decreasing life expectancy and increasing risk of other health issues. It is a leading preventable cause of death across the world. There are many medical problems that arise related to obesity, some of the most prominent being type 2 diabetes, heart disease, certain types of cancer and osteoarthritis. For type 2 diabetes in particular, the connection appears strongest: excess body fat underlies 64% of cases of diabetes in men and 77% of cases in women. It is unclear whether these problems are directly caused by obesity or if the poor diet and lack of physical exercise that lead to obesity, also lead to these conditions. Health conditions linked with diabetes fall into general categories: consequences resulting from the strain of increased mass on the body (osteoarthritis, sleep apnea) and those resulting from the increased amount of fat cells (cancer, cardiovascular disease, diabetes, non-alcoholic fatty liver disease).
Obesity has risen to prominence in recent decades due to its increased prevalence. In 1997, obese American adults constituted 19.4% of the population. By 2004 that had increased to 24.5% and in 2008 (the latest year for which data is available) was estimated at over 30%. If current trends continue, by 2015 41% of adults will be obese. However, some current studies suggest the rate of the rise of obesity may be slowing either due to health-related efforts or biological limits. Because obesity and health risks are so closely related, the large amount of obese adults has led to increased healthcare spending. It is estimated that obesity costs the country $147 billion a year in weight-related healthcare costs.
In addition to the adult population, obesity has significantly increased among children and adolescents. Estimates say that 25 million children, or 32% of the population, are obese or overweight, with 9 million, or 11.9%, qualifying as obese. One third of children born in or after 2000 will eventually have diabetes and many others will suffer chronic weight related problems such as high blood pressure, asthma, cancer and heart disease.
All statistics, unless otherwise stated, are from the Center for Disease Control and prevention.