Obesity paradox

Obesity paradox, also more inclusively known as reverse epidemiology, is a term for a medical hypothesis which holds that obesity (and high cholesterol, when the more global term reverse epidemiology is used) may, counterintuitively, be protective and associated with greater survival in certain groups of people, such as very elderly individuals or those with certain chronic diseases. It further postulates that normal to low body mass index or normal values of cholesterol may be detrimental and associated with higher mortality in asymptomatic people.

The terminology reverse epidemiology was first proposed by Kamyar Kalantar-Zadeh in the journal Kidney International in 2003 and in the Journal of the American College of Cardiology in 2004. It is a contradiction to prevailing concepts of prevention of atherosclerosis and cardiovascular disease; however, active prophylactic treatment of heart disease in otherwise healthy, asymptomatic people is and has been controversial in the medical community for several years.

The mechanism responsible for this reversed association is unknown, but it has been suggested that, in chronic kidney disease patients, "The common occurrence of persistent inflammation and protein energy wasting in advanced CKD seems to a large extent to account for this paradoxical association between traditional risk factors and CV outcomes in this patient population." Other research has proposed that the paradox may be explained by adipose tissue storing lipophilic chemicals that would otherwise be toxic to the body.

The obesity paradox (excluding cholesterol paradox) was first described in 1999 in overweight and obese people undergoing hemodialysis, and has subsequently been found in those with heart failure, myocardial infarction, acute coronary syndrome, and chronic obstructive pulmonary disease (COPD).

In people with heart failure, those with a body mass index between 30.0–34.9 had lower mortality than those with what would normally be considered an ideal weight. This has been attributed to the fact that people often lose weight as they become progressively more ill. Similar findings have been made in other types of heart disease. People with class I obesity and heart disease do not have greater rates of further heart problems than people of normal weight who also have heart disease. In people with greater degrees of obesity, however, risk of further events is increased. Even after cardiac bypass surgery, no increase in mortality is seen in the overweight and obese. One study found that the improved survival could be explained by the more aggressive treatment obese people receive after a cardiac event. Another found that if one takes into account COPD in those with PAD the benefit of obesity no longer exists.