Obesity is a medical condition, sometimes considered a disease, in which abnormal or excess body fat has accumulated to such an extent that it may have a negative effect on health. People are classified as obese when their body mass index (BMI)—a measurement obtained by dividing a persons weight by the square of the persons height (despite known allometric inaccuracies)—is over 30 kg/m2; the range 25–30 kg/m2 is defined as overweight. Some East Asian countries use lower values to calculate obesity.Obesity is a major cause of disability and is correlated with various diseases and conditions, particularly cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, and osteoarthritis. High BMI is a marker of risk for, but not a direct cause of, diseases caused by diet and physical activity. A reciprocal link has been found between obesity and depression, with obesity increasing the risk of clinical depression, and also depression leading to a higher chance of developing obesity.Obesity has individual, socioeconomic, and environmental causes. Some of the known causes are diet, physical activity, automation, urbanization, genetic susceptibility, medications, mental disorders, economic policies, endocrine disorders, and exposure to endocrine-disrupting chemicals. Epidemiologic studies of overweight and obesity in children and adults covering 195 countries have shown that the prevalence of obesity has steadily increased in most countries, doubling in 73 countries between the years 1980 and 2015. As of 2015, the United States and China had the largest numbers of obese adults, and China and India had the largest numbers of obese children.
They also had more than 12 times as many lost work days. The most common injuries in this group were due to falls and lifting, thus affecting the lower extremities, wrists or hands, and backs. The Alabama State Employees Insurance Board approved a controversial plan to charge obese workers $25 a month for health insurance that would otherwise be free unless they take steps to lose weight and improve their health. These measures started in January 2010 and apply to those state workers whose BMI exceeds 35 kg/m2 and who fail to make improvements in their health after one year.Some research shows that obese people are less likely to be hired for a job and are less likely to be promoted. Obese people are also paid less than their non-obese counterparts for an equivalent job; obese women on average make 6% less and obese men make 3% less.Specific industries, such as the airline, healthcare and food industries, have special concerns. Due to rising rates of obesity, airlines face higher fuel costs and pressures to increase seating width. In 2000, the extra weight of obese passengers cost airlines US$275 million. The healthcare industry has had to invest in special facilities for handling severely obese patients, including special lifting equipment and bariatric ambulances. Costs for restaurants are increased by litigation accusing them of causing obesity.