Obesity is a medicalcondition in which excess body fat has accumulated to the extent that it may have anadverse effect on health, leading to reduced lifeexpectancy and/or increased health problems. Body (BMI), a measurementwhich compares weight and height, defines people as overweight(pre-obese) when their BMI is between 25 kg/m2 and30 kg/m2, and obese when it is greater than 30 kg/m2.
Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, breathing difficulties during sleep,certain types of cancer,and osteoarthritis. Obesity is most commonly caused by a combination ofexcessive dietarycalories, lack of physical activity, and genetic susceptibility, although a few casesare caused primarily by genes,endocrinedisorders, medicationsor psychiatric illness. Evidence to support theview that some obese people eat little yet gain weight due to a slow metabolismis limited; on average obese people have a greater energy expenditure thantheir thin counterparts due to the energy required to maintain an increasedbody mass.
The primary treatment for obesity is dieting and physicalexercise. To supplement this, or in case of failure, anti-obesitydrugs may be taken to reduce appetite or inhibit fat absorption. In severecases, surgery is performed or an intragastric balloonis placed to reduce stomach volume and/or bowel length, leading to earliersatiation and reduced ability to absorb nutrients from food.
Obesity is a leading preventable cause of death worldwide,with increasing prevalence in adults and children,and authorities view it as one of the most serious publichealth problems of the 21st century. Obesity is stigmatizedin the modern Western world, though it has been perceived as asymbol of wealth and fertility at other times in history, and still is in manyparts of Africa.
Effects on health
Excessive body weight is associated with various diseases,particularly cardiovascular diseases, diabetes mellitus type 2, obstructive sleep apnea, certain types of cancer, and osteoarthritis.As a result, obesity has been found to reduce lifeexpectancy.
Obesity is one of the leading preventable causes of death worldwide.Large-scale American and European studies have found that mortality risk islowest at a BMI of 22.5–25 kg/m2 in non-smokers and at24–27 kg/m2 in current smokers, with risk increasing along withchanges in either direction. A BMI above 32 has been associated with a doubled mortalityrate among women over a 16-year period. In the United States obesity isestimated to cause an excess 111,909 to 365,000 death per year, while 1 million(7.7%) of deaths in the European Union are attributed to excess weight. Onaverage, obesity reduces life expectancy by six to seven years a BMI of30–35 reduces life expectancy by two to four years, while severe obesity(BMI > 40) reduces life expectancy by 10 years.
Obesity increases the risk of many physical and mental conditions. Thesecomorbidities are most commonly shown in metabolic syndrome, a combination of medicaldisorders which includes; diabetes mellitus type 2, high bloodpressure, high blood cholesterol, and high triglyceride levels.
Complications are either directly caused by obesity or indirectly relatedthrough mechanisms sharing a common cause such as a poor diet or a sedentary lifestyle. The strength of the linkbetween obesity and specific conditions varies. One of the strongest is thelink with type 2 diabetes. Excess body fat underlies 64% ofcases of diabetes in men and 77% of cases in women.
Health consequences fall into two broad categories: those attributable tothe effects of increased fat mass (such as osteoarthritis,obstructive sleep apnea, socialstigmatization) and those due to the increased number of fat cells (diabetes,cancer, cardiovascular disease, non-alcoholic fatty liver disease).Increases in body fat alter the body's response to insulin, potentially leadingto insulin resistance. Increased fat also creates aproinflammatorystate and a prothrombotic state
Obesity survival paradox
Although the negative health consequences of obesity in the generalpopulation are well supported by the available evidence, health outcomes incertain subgroups seem to be improved at an increased BMI, a phenomenon knownas the obesity survival paradox. The paradox was first described in 1999 inoverweight and obese people undergoing hemodialysis and has subsequently beenfound in those with heart failure and peripheral artery disease (PAD).
In people with heart failure, those with a BMI between 30.0–34.9 had lowermortality than those with a normal weight. This has been attributed to the factthat people often lose weight as they become progressively more ill. Similarfindings have been made in other types of heart disease. People with class Iobesity and heart disease do not have greater rates of further heart problemsthan people of normal weight who also have heart disease. In people withgreater degrees of obesity, however, risk of further events is increased. Evenafter cardiac bypass surgery, no increasein mortality is seen in the overweight and obese. One study found that theimproved survival could be explained by the more aggressive treatment obesepeople receive after a cardiac event. Another found that if one takes intoaccount chronic obstructive pulmonarydisease (COPD) in those with PAD the benefit of obesity no longer exists.